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Vogel'sQualitative Inorganic Analysis Seventh Edition Revised by G. Svehla PhD, DSC, FRSC formerly Professor of Analyti. VOGEL Química Analítica Qualitativa cittadelmonte.info - Ebook download as PDF File .pdf ), Text File .txt) or read book online. No encontramos nenhuma. Search quimica analtica qualitativa vogel pdf geometria analitica parabola 1. Contedo premium qumica. Quimica analitica.


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VOGEL Química Analítica Qualitativa cittadelmonte.info Leandro L Cavalheiro. Vogel's Qualitative Inorganic Analysis Seventh Edition Revised by G. Svehla PhD, DSC, . Vogel-Quimica Analitica Qualitativa(1aEd). Pages · · MB · Vogel's - Textbook of quantitative chemical analysis (5th Edition. Vogel Quimica Analitica Qualitativa(1aEd ). Uploaded by liobittencourt. química analitica qualitativa Download as PDF or read online from Scribd.

Revised by G. All rights reserved; no part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without either the prior written permission of the Publishers or a licence permitting restricted copying in the United Kingdom issued by the Copyright Licensing Agency Ltd. Trademarks Throughout this book trademarked names are used. Rather than put a trademark symbol in every occurrence of a trademarked name, we state that we are using the names only in editorial fashion and to the benefit of the trademark owner with no intention of infringement of the trademark. Preface to seventh edition ix From preface to the first edition x From preface to the fifth edition x From preface to the sixth edition xi.

Two postgraduate students in Cork, Miss Drewan McCaul and Mr Ronan Ennis, have carried out most of the atomic spectrometric tests experimentally; I wish to thank them for their efforts and I hope they will find the experience useful in their professional life.

As in the past, any suggestions for improvement will be welcomed by the revisor. Svehla I wanted to preserve all that made this popular book so good: The fourth edition has now been in use for more than twenty years.

Vogel Woolwich Polytechnic London S. Since Dr Vogel died in When undertaking the enormous task. The ultimate object was to provide a text-book at moderate cost which can be employed by the student continuously throughout his study of the subject.

From preface to the first edition Experience of teaching qualitative analysis over a number of years to large numbers of students has provided the nucleus around which this book has been written. The writer would be glad to hear from teachers and others of any errors which may have escaped his notice: It is the author's opinion that the theoretical basis of qualitative analysis.

When preparing the sixth edition. With the advent of more complex. With this aim in mind The new edition is aimed more to be a laboratory manual than a textbook. From preface to the sixth edition Previous editions of Vogel's Qualitative Inorganic Analysis were used mainly as university textbooks. The chemical change or its absence is observed and used for the elucidation of sample composition.

Chapter 3 contains the reactions of the most common cations. These are described to the necessary extent in most introductory chemistry texts and also in the first chapter of the 5th Edition of this book. This is usually done in two distinct steps. Chapter 1 -. Such a background involves chemical symbols.

Chapter 2 describes the laboratory equipment and skills necessary for such tests. In order to be able to do such analyses it is essential to study these reactions in a systematic way. This is followed with quantitative analysis. The intelligent study of qualitative inorganic analysis requires a certain level of theoretical background in general and inorganic chemistry. These can be divided broadly into two categories: Longman After a few weeks spent in the qualitative analytical laboratory the young chemists become familiar with solids.

Once the reader is familiar with these. The book is concluded with the reactions of the less common ions Chapter 6. The present book describes the traditional methods of qualitative inorganic analysis. It must be emphasized that the study of 'classical' qualitative inorganic analysis is invaluable for any intending chemist. The disposal of waste solutions must also be given serious consideration. Students and experienced chemists alike should always follow good laboratory practice GLP.

In many countries there are special regulations governing the acquisition and disposal of radioactive materials among which uranium and thorium are mentioned in this book. If necessary or if in doubt one must use fume cupboards with good ventilation.

This normally relates not only to the use of certain toxic substances but also to their labelling and storage. Students must be supervised during practicals by adequately trained personnel.

It is important to consult appropriate safety legislation that is extant in your country. It is worthwhile to spend some time at the beginning of a practical course on explaining safety measures in the laboratory.

When special care is needed e. It is prudent to keep a written record of such safety courses. It should be remembered that samples themselves often contain substances which are environmentally hazardous. A person should never work alone in a laboratory.

Safety glasses must be worn at all times and in many cases suitable gloves should be used. For micro analysis the factor is of the order of Qualitative analysis may be carried out on various scales.

In macro analysis the quantity of the substance employed is 0. Experimental techniques Chapter 2 2. The special operations needed for semimicro and micro work will be discussed in somewhat more detail. In what is usually termed semimicro analysis these quantities are reduced by a factor of The readers should familiarize themselves first with macro operations. We begin with the discussion of the most important dry tests.

Sulphur dioxide can result when heating sulphites. Sublimation may take place. The former are applicable to solid substances. The most common changes are associated with the removal of water of crystallization. Heating Subl imation Colour change Gases 4 I. Among micro scale operations. Nitrates yield nitrogen dioxide. Colour change can occur. Oxygen is obtained if chi orates. When heating ammonium salts mixed with alkalis. Gases produced may be colourless or coloured.

The information obtained in a comparatively short time often provides a clue to the presence or absence of certain substances. Qualitative analysis utilizes two kinds of tests. Carbon dioxide can form if certain carbonates or organic materials are present. Small test-tubes. Heating cyanides yields cyanogen. Heating the substance is placed in a small ignition tube bulb tube. The deposit can be black if mercury I or II sulphides are present. Sublimation yields a deposit of solid substance in the upper.

With this knowledge the course of wet analysis may be modified and shortened. Instructions for some important dry tests are given below. A white deposit occurs if ammonium salts. Chlorine occurs if certain chlorides e. They can be identified with appropriate reagents. A yellow deposit originates from sulphur. It may be said that when the general technique of semimicro analysis has been mastered and appreciated. Blowpipe tests a luminous Bunsen flame air holes completely closed.

Zinc yields an incrustation which is yellow while hot and white when cold. The oxides of the noble metals silver and gold are decomposed. Figure 2. A reducing flame is produced by placing the nozzle of a mouth blowpipe just outside the flame. The oxides of cadmium. The oxides of lead. The alkali salts are largely adsorbed by the porous charcoal. The final products of the reaction are therefore either the metals alone.

Dry tests 2. The oxides of the metals may further decompose. The tests are carried out upon a clean charcoal block in which a small cavity has been made with a penknife or with a small coin. Crystalline salts break into smaller pieces. The initial reaction consists of the formation of the carbonates of the cations present and the alkali salts of the anions. More frequently the powdered substance is mixed with twice its bulk of anhydrous sodium carbonate or.

The oxides thus formed are deposited as an incrustation round the cavity of the charcoal block. A little of the substance is placed in the cavity and heated in the oxidizing flame. An oxidizing flame is obtained by holding the nozzle of the blowpipe about one-third within the flame and blowing somewhat more vigorously in a direction parallel with the burner top.

The non-luminous Bunsen flame consist of thee parts: I an inner blue cone ADB cor. If the white residue or white incrustation left on a charcoal block is treated with a drop of cobalt nitrate solution and again heated. The principal parts of the flame. Flame tests in order to understand the operations involved in the flame colour tests and the various bead tests to be described subsequently Flame tests on dry samples 3.

The hottest part of the flame is the fusion zone at b and lies at about one-third of the height of the flame and approximately equidistant I 6 A blue colour is also given by phosphates. A characteristic incrustation accompanies the globules of lead.

Lower oxidizing zone c C H. Hottest portion of flame b 0. The oxides of aluminium. Lower reducing zone f 1: The lowest temperature is at the base of the flame a. The lower oxidizing zone c is situated on the outer border of b and may be used for the oxidation of substances dissolved in beads of borax. Repeat the test Table 2. The chlorides are among the most volatile compounds. It may be used for all oxidation processes in which the highest temperature is not required. Less volatile substances are heated in the fusion zone b.

The procedure is as follows. A thin platinum wire about 5 cm long and 0. The wire is dipped into concentrated hydrochloric acid on a watch glass. The colours imparted to the flame by salts of different metals are shown in Table 2. Compounds of certain metals are volatilized in a non-luminous Bunsen flame and impart characteristic colours to the flame.

It is then introduced into the lower oxidizing zone c. The upper oxidizing zone d consists of the nonluminous tip of the flame. Carry out flame tests with the chlorides of sodium. This is first thoroughly cleaned by dipping it into concentrated hydrochloric acid contained in a watch glass and then heating it in the fusion zone b of the Bunsen flame. The upper reducing zone e is at the tip of the inner blue cone and is rich in incandescent carbon.

We can now return to the flame tests. The conspicuous lines are located on a graph drawn. A coating of potassium hydrogen sulphate is made to adhere to the wire by drawing the hot wire across a piece of the solid salt. It is a good plan to store the wire permanently in the acid. Upon passing the wire slowly through a flame. A cork is selected that just fits into a test-tube. Repeat all the tests with a cobalt glass and note your observations.

When cool. Table 2. Any small residue of pyrosulphate dissolves at once in water. The yellow colouration due to the sodium masks that of the potassium. It consists of a collimator A which throws a beam of parallel rays on the prism B. It is then best to employ fused potassium hydrogen sulphate. The instrument employed to resolve light into its component colours is called a spectroscope.

The spectroscope 8 4. A simple form is shown in Fig. It is therefore possible to detect potassium in the lower oxidizing flame and the calcium.

The resulting bright clean platinum wire imparts no colour to the flame. View the flame through two thicknesses of cobalt glass. Potassium chloride is much more volatile than the chlorides of the alkaline earth metals. A platinum wire sometimes acquires a deposit which is removed with difficulty by hydrochloric acid and heat. After all the tests. The spectroscope is calibrated by observing the spectra of known substances. The testtube is about half filled with concentrated hydrochloric acid so that when the cork is placed in position.

Spectroscopic tests flame spectra the best way to employ flame tests in analysis is to resolve the light into its component tints and to identify the cations present by their characteristic sets of tints. The sodium line is then sharply focused by suitably adjusting the sliding tubes of the collimator and the telescope. Dry tests Components of a spectroscope: This light passes through an achromatic objective lens 9.

Some sodium chloride is introduced by means of a clean platinum wire into the lower part of the flame. The slit should also be made narrow in order that the position of the lines on the scale can be noted accurately. When the comparison prism is interposed. The light from the flame passes along the central axis of the instrument through the slit. To adjust the simple table spectroscope described above which is always mounted on a rigid stand.

The wavelength curve may then be employed in obtaining the wavelength of all intermediate positions and also in establishing the identity of the component elements of a mixture.

A smaller. If available. There is a subsidiary tube adjacent to the main tube: If a sodium compound is introduced into the colourless Bunsen flame. The resulting spectrum. The scale is calibrated directly into divisions of 10 nanometers or A in older instruments and has also an indication mark at the D-line: By narrowing the slit.

An adjusting screw is provided to alter the position of the right angle prism in order to adjust the scale relative to the spectrum. The elements which are usually identified by the 0 The old units of angstrom A. It is focused by means of a lens system comprising two achromatic combinations between which is a right angle prism.

The train of prisms gives an angular dispersion of about 11 between the red and the blue ends of the spectrum. This prism turns the beam of light so that it falls on the face of the end prism of the train of five prisms and is reflected into the observer's eye. The mean wavelength of these two lines is 5. The instrument can be mounted on a special stand. Borax bead tests a platinum wire. If the resolution of the spectroscope is small.

The loop is heated in the Bunsen flame until it is red hot and then quickly dipped into powdered borax. As already stated. These tests will be described under Section 2. Dry tests Table 2. Borax bead test 5. According to their procedure. Tests for certain metals can be carried out conveniently on solutions using flame atomic emission spectrometry F AES or flame atomic absorption spectrometry FAAS.

It is the author's experience that the loop method is far more satisfactory. The danger of the bead falling off is reduced by holding the wire horizontally. The adhering solid is held in the hottest part of the flame. The spectra of the various elements are shown diagrammatically in Fig.

The wavelengths of the brightest lines. The free end of the platinum wire is coiled into a small loop through which an ordinary match will barely pass.

The bead and adhering substance are first heated in the lower reducing flame.. They are then heated in the lower oxidizing flame.. It is important to employ a minute amount of substance as otherwise the bead will become dark and opaque in the subsequent heating.. Carry out borax bead tests with salts of these metals and compare results with those given in Chapter 3. Fe B02h and Fe B02h are formed in the reducing and oxidizing flames respectively. Thus a blue phosphate bead is obtained with cobalt salts: After each test.

Thus with copper salts in the oxidizing flame. The borax bead also provides an excellent method for cleaning a platinum wire. Phosphate or microcosmic salt bead tests the bead is produced similarly to the borax bead except that microcosmic salt. Some authors assume that the metal metaborate combines with sodium metaborate to give complex borates of the type Na2[Cu B02 4]. In certain circumstances the borax-bead test is inconclusive.

The colourless. In the reducing flame i. Microcosmic salt bead test 6. The coloured borax beads are due to the formation of coloured borates. They accordingly adhere better to the platinum wire loop. Yellow when hot. Grey when cold..

Tungsten Yellow when hot. Colourless when hot. This reaction is employed for the detection of silicates: Pale yellow when hot. In general.

Green when cold. Titanium " Blood red when fused with a trace of iron II sulphate. When a silicate is strongly heated in the bead. Conical or Erlenmeyer flasks these should be of If this is moistened. The rods should be about 20 em long for use with test-tubes and em long for work with basins and small beakers. Clock glasses of the appropriate size should be provided. For heating moderate volumes of liquids a somewhat larger tube. The following general notes on basic laboratory operations should be carefully studied.

For evaporations and chemical reactions which are likely to become vigorous. Wet reactions on macro scale 2. Open glass tubes must not be used as stirring rods.

The majority of reactions in qualitative analysis are carried out in solution. Sodium carbonate bead tests the sodium carbonate bead is prepared by fusing a small quantity of sodium carbonate on a platinum wire loop in the Bunsen flame.

Vogel Quimica Analitica Qualitativa(1aEd 1981)

Stirring rods a length of glass rod. Beakers those of A rod pointed at one end. Such reactions lead to: A test-tube brush should be available for cleaning the tubes.

Smaller test-tubes are sometimes used for special tests. The introduction of a funnel. It is useful to remember that 10 ml of liquid fills a test-tube of this size to a depth of about 5.

Test-tubes the best size for general use is 15 x 2 cm with 25 ml total capacity. The various colours of the phosphate beads are collected in Table 2. Equipment 1. Precipitation with hydrogen sulphide operations with hydrogen sulphide are of such importance in qualitative inorganic analysis that they merit detailed discussion. These flasks cannot be heated.

Precipitation 6. A stirring rod of polythene polyethylene with a thin fan-shaped paddle on each end is available commercially and functions as a satisfactory 'policeman' at laboratory temperature: Wash bottle this may consist of a ml flat-bottomed flask.

The flow rate can easily be regulated by changing the pressure exerted by the hand. A rubber bulb may be attached to the short tube. This is usually best detected by filtering a little of the mixture and testing the filtrate with the reagent. How to use H 2 S safely and sparingly 7.

Polyethylene wash bottles Fig. It should always be borne in mind that a large excess of the precipitating agent may lead to the formation of complex ions and consequent partial solution of the precipitate.

A rubber-tipped glass rod or 'policeman' is employed for removing any solid from the sides of glass vessels. As the air bubbles through the liquid. When set aside the walls flatten out again and air is sucked into the bottle through the tube. In most cases.

Vogel Quimica Analitica Qualitativa(1aEd 1981)

When studying the reactions of ions the concentrations of the reagents are known and it is possible to judge the required volume of the reagent by quick mental calculation. Insulating cloth should be wound round the neck of the flask in order to protect the hand.

Precipitation when excess of a reagent is to be used in the formation of a precipitate. It is recommended that the wash bottle be kept ready for use filled with hot water as it is usual to wash precipitates with hot water. The pressure pushes the liquid out through the tube. Hydrogen sulphide gas is highly poisonous.

In order to ensure that all the air has been expelled. C is a stopcock which controls the flow of gas from the generator. The 'bubbling' method is not recommended and should not be used for macro analysis. The solution is contained in a small conical flask A. One method. Fortunately its unpleasant smell repels people from breathing in dangerous amounts. B is a wash bottle containing water and serves to remove any hydrochloric acid spray that might be carried over from the Kipp's apparatus in the gas stream.

The stopper is first loosened in the neck of the flask and the gas stream turned on C first. The most satisfactory procedure the 'pressure' method is best described with the aid of Fig. The conical flask is connected to the wash bottle by a short length of rubber tubing. Hydrogen sulphide must be handled in a fume cupboard with good ventilation. Passage of the gas is continued 3 Stopcock D is optional. With the gas flowing.

The efficiency of the method is low. Filtration Washing 8. Filter paper pulp increases the speed of filtration by retaining part of the precipitate and thus preventing the clogging of the pores of the filter paper.

It should never be more than about twothirds full of the solution. Filtration and washing the purpose of filtration is. A precipitate may be washed by decantation. Such a reagent can most conveniently be used in teaching laboratories or classroom demonstrations when studying the reactions of ions. Gelatinous precipitates. Liquids containing precipitates should be heated before filtration except in special cases.

Displacement of the gas in the flask by loosening the stopper when the bubbling has diminished considerably will ensure complete precipitation. When a precipitate tends to pass through the filter paper. This can most easily be prepared in the bottle B of the apparatus shown in Fig. This procedure is unnecessary for 4 It must be borne in mind that the gas may contain a small proportion of hydrogen due to the iron usually present in the commercial iron II sulphide.

The delivery tube must be thoroughly cleaned after each precipitation. The size of the filter paper is controlled by the quantity of precipitate and not by the volume of the solution. Complete precipitation should be tested for by separating the precipitate by filtration. The advantages of the 'pressure' method are: I a large surface of the liquid is presented to the gas and 2 it prevents the escape of large amounts of unused gas. The same device can be put together with glass joints.

The upper edge of the filter paper should be about 1 cm from the upper rim of the glass funnel. Occasionally a test-tube replaces the conical flask. A moderately fine-textured filter paper is generally employed. For a quantitative precipitation of sulphides e. The best method is to add a little filter paper pulp macerated filter paper to the solution and then to filter in the normal manner. The lower end of the tube or of the funnel should touch the side of the vessel in which the filtrate is being collected in order to avoid splashing.

The speed of filtration depends inter alia upon the length of the water column. Aids to filtration the simplest device is to use a funnel with a long stem. Removal of precipitate from the filter Filtration aids and techniques Using suction 9. When only a small quantity of the precipitate is available. The side arm of the flask is connected by means of thick-walled rubber tubing 'pressure' tubing to another flask. Upon applying suction to the filter paper fitted into the funnel in the usual way.

This is most readily done by pouring the solvent. Removal of the precipitate from the filter if the precipitate is bulky. The completion of washing. This is best done by directing a stream of water from a wash bottle first around the upper rim of the filter and following this down in a spiral towards the precipitate in the apex. In the first. If the amount of precipitate is small. In the second. A filter flask of ml capacity is fitted with a two-holed rubber bung.

To surmount the difficulty. If it is desired to maintain a small volume of the liquid. Other test papers are employed similarly.

It is frequently necessary to dissolve a precipitate completely. If the solution is to be tested for acidity or alkalinity. For this purpose either a Whatman filter cone No. Filtration with suction can be achieved by components with glass joints. This consists of a porcelain funnel in which a perforated plate is incorporated.

The most rapid evaporation is achieved by heating the dish directly on a wire gauze. They may be filtered through a small pad of glass wool placed in the apex of a glass funnel.

The Buchner funnel is fitted into the filter flask by means of a cork. Both types of support are folded with the filter paper to form the normal type of cone Fig. When filtration is complete. Strongly acidic or alkaline solutions cannot be filtered through ordinary filter paper. A more convenient method. The Jena 'slit sieve' funnel. Evaporation the analytical procedure may specify evaporation to a smaller volume or evaporation to dryness.

When the volume of liquid is small. For many purposes a water bath a beaker half-filled with water maintained at the boiling point is quite suitable will Fig. For a large quantity of precipitate. Two thicknesses of well-fitting filter paper cover the plate. Filtration is carried out under reduced pressure exactly as with a Buchner funnel. Both operations can be conveniently carried out in a porcelain evaporating dish or casserole.

After the filter paper has been supported in the funnel. The reduction in volume of a solution may also be accomplished by direct heating in a small beaker over a wire gauze or by heating in a wide test-tube 'boiling-tube'. It consists -. A useful anti-bumping device. Should corrosive fumes be evolved during the evaporation. Wet reactions on macro scale b a c 2. When evaporating to dryness. More complete drying is obtained by placing the funnel containing the filter paper in a 'drying cone' a hollow tinned-iron cone or cylinder.

Glass apparatus which appears to be particularly dirty or greasy is cleaned by soaking in chromosulphuric acid concentrated sulphuric acid containing about g of potassium dichromate per litre.

Drying of precipitates partial drying. The size of the Bunsen flame should be no larger than is absolutely necessary. The device must not be used in solutions that contain a precipitate. The funnel is thus exposed to a current of hot air. Other apparatus. All glass and porcelain apparatus must be scrupulously clean.

Neither strong acids nor strong alkalis should be thrown into the sink. If this is not the case. Reagents should always be added portion-wise. Test-tubes may be inverted in the test-tube stand and allowed to drain. Avoid using unnecessary excess of reagents. If a reagent bottle is empty. Drying precipitates Great care must be taken not to char the filter paper. A test-tube brush should be used to clean test-tubes and other glass apparatus.

The cleaning agent is highly corrosive! Tidiness Cleanliness Not wasting chemicals Waste disposal 22 Cleaning of apparatus Remember a tidy bench is indicative of a methodical mind. A string duster is useful to wipe up liquids split upon the bench. It should be extinguished when no longer required. Some working hints a Always work in a tidy. Cleaning of apparatus the importance of using clean apparatus cannot be too strongly stressed.

A safer but slower method is to place the funnel and filter paper. They should be returned to their correct places upon the shelves immediately after use.

A few minutes should be devoted at the end of the day's work to 'cleaning up'. All glassware should be put away clean. Apart from inaccuracies which may thus creep in. Semimicro operations Fume cupboard Taking notes 2.

When a precipitate is to be separated by centrifuging. Solids corks. The sharp edges are fire-polished by heating momentarily in a flame. A handle may be formed. These can readily be made by cutting 2 mm diameter glass rod into 12 cm lengths. For rapid concentration of a solution by means of a free flame.

Since volumes of the order of 1 ml are dealt with. Stirring rods solutions do not mix readily in semimicro test-tubes and centrifuge tubes. Test-tubes and centrifuge tubes small Pyrex test-tubes usually 75 x lOmm. Various sizes are available. It is a good plan to cover these with filter paper to prevent the entrance of dust.

The writing up of experiments should not be postponed until after one has left the laboratory. Semimicro apparatus and semimicro analytical operations The essential technique of semi micro analysis does not differ very greatly from that of macro analysis. Particular care must be directed to having both the apparatus and the work bench scrupulously clean. In washing a precipitate with water or other liquid. On no account may they be thrown into the sink.

The various operations occupy less time and the consumption of chemicals and glassware is reduced considerably. Test-tubes 1. Stirring 2.

Two varieties are shown in Fig. Dropper b will be referred to as a capillary dropper. Droppers for handling liquids in semimicro analysis. Droppers 3. Introduce some distilled water into the clean dropper by dipping the capillary end into some distilled water in a beaker and compressing and then releasing the rubber teat or bulb. Hold the dropper vertically over a clean dry 5 ml measuring cylinder.

Before use the droppers must be calibrated.. The former one finds application in 30 or 60 ml reagent bottles and may therefore be called a reagent dropper. Repeat the calibration until two results are obtained which do not differ by more than 2 drops. A list of such reagents is given in Table 2. The other reagents. It must be remembered that the volume of the drop delivered by a dropper pipette depends upon the density.

When using these side shelf reagents. A dropping bottle of 30 ml capacity with an interchangeable glass cap Fig. The bottles a and b cannot be used for concentrated acids and other corrosive liquids because of their action upon the stoppers. The dropper should deliver between 30 and 40 drops per m!. This dropper is somewhat more robust than that shown in Fig. Those reagents which are most frequently used should be kept by each worker separately. These dropping bottles Fig.

Calculate the volume of a single drop. Semimicro operations b. If the dropper delivers 20 drops of distilled water. Reagent bottles and reagents a semimicro reagent bottle may be easily constructed by inserting a reagent dropper through a cork or rubber stopper that fits a 30 or 60 ml bottle. Attach a small label to the upper part of the dropper giving the number of drops per m!. For the study of reactions it is best to divide reagents into two groups. Count the number of drops until the meniscus reaches the 2 ml mark.

Scm 2. The standard commercial form of medicine dropper. The simplest containers for these corrosive liquids are 30 or 60 ml dropping bottles with glass stopper containing a groove the so-called 'TK bottle'. Under no circumstances should the capillary end of the dropper be dipped into any foreign solution. In practice. Centrifuge Table 2.

Ammonia solution. SM Acetic acid. If accidental contact should be made. Nitric acid. Sulphuric acid. This is an apparatus for the separation of two substances of different density by the application of centrifugal force which may be several times that of gravity. The tube and its contents. The centrifuge the separation of a precipitate from a supernatant liquid is carried out with the aid of a centrifuge.

This operation centrifugation replaces filtration in macro analysis. The buckets can either 'swing out' to the horizontal position or.. O i l here Fig. Spilling may corrode the buckets and produce an unbalanced head.. A small 2-tube hand centrifuge with protecting bowl and cover Fig. The advantages of centrifugation are: In the latter case. Several types of centrifuge are available for semimicro analysis.

These are: The central spindle should be provided with a locking screw or nut: An inexpensive constant speed. When using a centrifuge. The hand-driven centrifuge is inexpensive and is satisfactory in most cases.. Semimicro operations Removable lid. A little practice will enable one to judge the exact time required to pack the precipitate tightly at the bottom of the tube. Most semimicro centrifuges will accommodate both semimicro test-tubes 75 x 10 mm and centrifuge tubes up to 5 ml capacity.

As the pressure is very slowly released the liquid rises in the dropper and the latter is lowered further into the liquid.

The centrifuge tube is held at an angle in the left hand. Do not attempt to retard the speed of the centrifuge with the hand. Maintain the maximum speed for seconds. Surface tension effects prevent surface particles from settling readily. Fix the cover in place. An unusual sound may be due to the breaking of a tube.

Agitate the surface with a stirring rod if necessary. The advantages of the latter include easier removal of the mother liquor with a dropper.

To remove the supernatant liquid. It is of the utmost importance to avoid strains or vibrations as these may result in stirring up the mixture and may damage the apparatus. If a suspicious sound is heard. Washing the precipitates it is essential to wash all precipitates in order to remove the small amount of solution present in the precipitate.

It is best to wash the precipitate at least twice. The wash liquid is usually water Semimicro operations 2. Great care should be taken as the capillary approaches the bottom of the centrifuge tube that its tip does not touch the precipitate. In difficult cases. Washing 6. The solution in the dropper should be perfectly clear. The wash liquid is a solvent which does not dissolve the precipitate but dilutes the quantity of mother liquor adhering to it..

Wash bottles for most work in semimicro analysis a 30 or 60ml glass stoppered bottle is a suitable container for distilled water. The supernatant liquid is removed by a capillary dropper. Transferring of precipitates in some cases precipitates can be transferred from semimicro test-tubes with a small spatula two convenient types in nickel or monel metal are shown in Fig.

A small conical flask 25 or 50 m! Wash bottles 7. For those who prefer wash bottles This operation is usually difficult Heating of solutions solutions in semimicro centrifuge tubes cannot be heated over a free flame owing to the serious danger of 'bumping' and consequent loss of part or all of the liquid in such narrow tubes.

The test-tube may be washed by holding it in an almost vertical upside down position with its mouth over the receptacle and directing a fine stream of solution or water from a capillary dropper onto the sides of the test-tube. The latter heating operation requires very careful manipulation and should not be attempted by beginners. This may consist of a ml Pyrex beaker. Heating solutions Water bath 9. The simplest procedure is to employ a small water bath. The danger of 'bumping' may be considerably reduced by employing the antibumping device shown in Fig.

It is a good plan to wind a thin rubber band about 5 mm from the top of Fig. Similar remarks apply to semimicro test-tubes. If the precipitate in a test-tube is to be treated with a reagent in an evaporating dish or crucible. The mouth of the test-tube must be pointed away from others nearby.

The 'bumping' or spattering of hot solutions may often be dangerous and lead to serious burns if the solution contains strong acids or bases. On the whole it is better to resort to safer methods of heating. Evaporations where rapid concentration of a liquid is required or where volatile gases must be expelled rapidly..

This rack will accommodate four centrifuge tubes and four semimicro test-tubes.. Useful holders The dimensions of a rack of smaller size are given in Fig. The apparatus is constructed of monel metal.

I Fig. A more elaborate arrangement which will. A little practice is required in order to achieve regular boiling by intermittent heating with a flame and also to avoid 'bumping' and spattering. This may be placed in an air bath consisting of a 30 ml nickel crucible and supported thereon by a ring Fig. This can result in an increased resistance against the reagent used for dissolution.

I wanted to preserve all that made this popular book so good: The ultimate object was to provide a text-book at moderate cost which can be employed by the student continuously throughout his study of the subject. Since Dr Vogel died in From preface to the first edition Experience of teaching qualitative analysis over a number of years to large numbers of students has provided the nucleus around which this book has been written.

When undertaking the enormous task. Vogel Woolwich Polytechnic London S. The writer would be glad to hear from teachers and others of any errors which may have escaped his notice: The fourth edition has now been in use for more than twenty years.

It is the author's opinion that the theoretical basis of qualitative analysis. With this aim in mind. When preparing the sixth edition. With the advent of more complex. From preface to the sixth edition Previous editions of Vogel's Qualitative Inorganic Analysis were used mainly as university textbooks.

The new edition is aimed more to be a laboratory manual than a textbook. Further- more. Once the reader is familiar with these. This is usually done in two distinct steps. Chapter 3 contains the reactions of the most common cations. Longman Chapter 1 Introduction The purpose of chemical analysis is to establish the composition of naturally occurring or artificially manufactured substances.

After a few weeks spent in the qualitative analytical laboratory the young chemists become familiar with solids. Chapter 2 describes the laboratory equipment and skills necessary for such tests. This is followed with quantitative analysis. These can be divided broadly into two categories: The book is concluded with the reactions of the less common ions Chapter 6. The present book describes the traditional methods of qualitative inorganic analysis.

It must be emphasized that the study of 'classical' qualitative inorganic ana- lysis is invaluable for any intending chemist. These are described to the necessary extent in most introductory chemistry texts and also in the first chapter of the 5th Edition of this book. In order to be able to do such analyses it is essential to study these reactions in a systematic way. Such a background involves chemical symbols.. If necessary or if in doubt one must use fume cupboards with good ventilation.

It is important to consult appropriate safety legislation that is extant in your country. Students must be supervised during practicals by adequately trained personnel.

The disposal of waste solutions must also be given serious consideration. It is worthwhile to spend some time at the beginning of a practical course on explaining safety measures in the laboratory.

When special care is needed e. In many countries there are special regulations governing the acquisition and disposal of radioactive materials among which uranium and thorium are mentioned in this book. It is prudent to keep a written record of such safety courses.

Safety glasses must be worn at all times and in many cases suitable gloves should be used. Students and experienced chemists alike should always follow good laboratory practice GLP. It should be remembered that samples them- selves often contain substances which are environmentally hazardous.

A person should never work alone in a laboratory. This normally relates not only to the use of certain toxic substances but also to their labelling and storage. In macro analysis the quantity of the substance employed is 0. Qualitative analysis may be carried out on various scales.

The readers should familiarize themselves first with macro operations. In what is usually termed semi- micro analysis these quantities are reduced by a factor of The special operations needed for semi- micro and micro work will be discussed in somewhat more detail.

Chapter 2 Experimental techniques 2. For micro analysis the factor is of the order of Nitrates yield nitrogen dioxide. The most common changes are associated with the removal of water of crystallization. They can be identified with appropriate reagents. Gases Gases produced may be colourless or coloured.

The deposit can be black if mercury I or II sulphides are present. With this knowledge the course of wet analysis may be modified and shortened. A white deposit occurs if ammonium salts. Chlorine occurs if certain chlorides e. Sulphur dioxide can result when heating sulphites. Oxygen is obtained if chi orates. It may be said that when the general technique of semi- micro analysis has been mastered and appreciated.

Heating I. The information obtained in a compara- tively short time often provides a clue to the presence or absence of certain substances. The former are applicable to solid substances. Carbon dioxide can form if certain carbonates or organic materials are present. Small test-tubes. Heating cyanides yields cyanogen. Qualitative analysis utilizes two kinds of tests. Among micro scale operations. Subl imation Sublimation yields a deposit of solid substance in the upper.

Instructions for some important dry tests are given below. A yellow deposit originates from sulphur. Colour change Colour change can occur.

Sublimation may take place. We begin with the discussion of the most important dry tests. When heating ammonium salts mixed with alkalis. Heating the substance is placed in a small ignition tube bulb tube. The oxides of lead. A little of the sub- stance is placed in the cavity and heated in the oxidizing flame. Crystalline salts break into smaller pieces. The final products of the reaction are therefore either the metals alone. The initial reaction consists of the formation of the carbonates of the cations present and the alkali salts of the anions.

More frequently the powdered sub- stance is mixed with twice its bulk of anhydrous sodium carbonate or. An oxidizing flame is obtained by holding the nozzle of the blowpipe about one-third within the flame and blowing somewhat more vigorously in a direction parallel with the burner top. The oxides of the noble metals silver and gold are decomposed. Blowpipe tests a luminous Bunsen flame air holes completely closed. The alkali salts are largely adsorbed by the porous charcoal.

Zinc yields an incrustation which is yellow while hot and white when cold. The oxides of the metals may further decompose. Dry tests 2. The oxides of cadmium. Figure 2. A reducing flame is produced by placing the nozzle of a mouth blowpipe just outside the flame.

The oxides thus formed are deposited as an incrustation round the cavity of the charcoal block. The tests are carried out upon a clean charcoal block in which a small cavity has been made with a penknife or with a small coin. Flame tests in order to understand the operations involved in the flame samples colour tests and the various bead tests to be described subsequently. Lower oxidizing zone c C H. A characteristic incrustation accompanies the globules of lead. The hottest part of the flame is the fusion zone at b and lies at about one-third of the height of the flame and approximately equidistant I A blue colour is also given by phosphates.

Hottest portion of flame b 0. If the white residue or white incrustation left on a charcoal block is treated with a drop of cobalt nitrate solution and again heated.. Flame tests on dry 3. The princi- pal parts of the flame. The non-luminous Bunsen flame consist of thee parts: I an inner blue cone ADB cor. The lowest temperature is at the base of the flame a.! Lower temperature zone a Fig. The oxides of aluminium.

Lower reducing zone f 1: The chlorides are among the most volatile com- pounds. The colours imparted to the flame by salts of different metals are shown in Table 2. It may be used for all oxidation processes in which the highest temperature is not required.

The lower oxidizing zone c is situated on the outer border of b and may be used for the oxidation of substances dissolved in beads of borax. Repeat the test Table 2. Compounds of certain metals are volatilized in a non-luminous Bunsen flame and impart characteristic colours to the flame. A thin platinum wire about 5 cm long and 0. The upper reducing zone e is at the tip of the inner blue cone and is rich in incandescent carbon.

The wire is dipped into concentrated hydrochloric acid on a watch glass.

Less volatile substances are heated in the fusion zone b. The proce- dure is as follows. Carry out flame tests with the chlorides of sodium. It is then introduced into the lower oxidizing zone c. We can now return to the flame tests. This is first thoroughly cleaned by dipping it into concentrated hydrochloric acid contained in a watch glass and then heating it in the fusion zone b of the Bunsen flame. The upper oxidizing zone d consists of the non- luminous tip of the flame.

Potassium chloride is much more volatile than the chlorides of the alkaline earth metals. It consists of a collimator A which throws a beam of parallel rays on the prism B. View the flame through two thicknesses of cobalt glass. When cool. It is therefore possible to detect potassium in the lower oxidiz- ing flame and the calcium. It is a good plan to store the wire permanently in the acid. A platinum wire sometimes acquires a deposit which is removed with difficulty by hydrochloric acid and heat.

A simple form is shown in Fig. The yellow colouration due to the sodium masks that of the potassium. The resulting bright clean platinum wire imparts no colour to the flame. Repeat all the tests with a cobalt glass and note your observations. After all the tests. Upon passing the wire slowly through a flame. Spectroscopic tests flame spectra the best way to employ flame tests in analysis is to resolve the light into its component tints and to identify the cations present by their characteristic sets of tints.

Any small residue of pyrosulphate dissolves at once in water. The instrument employed The spectroscope to resolve light into its component colours is called a spectroscope. It is then best to employ fused potassium hydrogen sulphate. A cork is selected that just fits into a test-tube.

The test- tube is about half filled with concentrated hydrochloric acid so that when the cork is placed in position. Table 2. A coating of potassium hydrogen sulphate is made to adhere to the wire by drawing the hot wire across a piece of the solid salt. The conspicuous lines are located on a graph drawn 8. The spectroscope is calibrated by observing the spectra of known sub- stances.

This light passes through an achromatic objective lens 9. The slit should also be made narrow in order that the position of the lines on the scale can be noted accurately.

If available. A smaller. The light from the flame passes along the central axis of the instrument through the slit. When the comparison prism is interposed. To adjust the simple table spectroscope described above which is always mounted on a rigid stand. Some sodium chloride is introduced by means of a clean platinum wire into the lower part of the flame. The wave- length curve may then be employed in obtaining the wavelength of all intermediate positions and also in establishing the identity of the component elements of a mixture.

The sodium line is then sharply focused by suitably adjusting the sliding tubes of the collimator and the telescope. It is focused by means of a lens system comprising two achromatic combinations between which is a right angle prism..

An adjusting screw is provided to alter the position of the right angle prism in order to adjust the scale relative to the spectrum. This prism turns the beam of light so that it falls on the face of the end prism of the train of five prisms and is reflected into the observer's eye.

There is a subsidiary tube adjacent to the main tube: The elements which are usually identified by the The resulting 0 spectrum The instrument can be mounted on a special stand.

If a sodium compound is introduced into the colourless Bunsen flame. The scale is calibrated directly into divisions of 10 nanometers or A in older instruments and has also an indication mark at the D-line: By narrowing the slit. The mean wavelength of these two lines is 5. The train of prisms gives an angular dispersion of about 11 between the red and the blue ends of the spectrum..

The old units of angstrom A. Borax bead test 5. It is the author's experience that the loop method is far more satisfactory. The spectra of the various elements are shown diagrammatically in Fig. If the resolution of the spectroscope is small.

The danger of the bead falling off is reduced by hold- ing the wire horizontally. These tests will be described under Section 2. Tests for certain metals can be carried out conveniently on solutions using flame atomic emission spectrometry F AES or flame atomic absorption spectrometry FAAS. The adhering solid is held in the hottest part of the flame.

Borax bead tests a platinum wire. The free end of the platinum wire is coiled into a small loop through which an ordinary match will barely pass. According to their procedure. As already stated. The loop is heated in the Bunsen flame until it is red hot and then quickly dipped into powdered borax.

The wavelengths of the brightest lines. They are then heated in the lower oxidizing flame. The bead and adhering substance are first heated in the lower reducing flame.

It is important to employ a minute amount of substance as otherwise the bead will become dark and opaque in the subsequent heating. Microcosmic salt bead 6. Fe B02h and Fe B02h are formed in the reducing and oxidizing flames respectively. Thus with copper salts in the oxidizing flame.

In certain circumstances the borax-bead test is inconclusive. Some authors assume that the metal metaborate combines with sodium metaborate to give complex borates of the type Na2[Cu B02 4]. Phosphate or microcosmic salt bead tests the bead is produced similarly test to the borax bead except that microcosmic salt. In the reducing flame i.

The coloured borax beads are due to the formation of coloured borates. Carry out borax bead tests with salts of these metals and compare results with those given in Chapter 3. The borax bead also provides an excellent method for cleaning a platinum wire. Thus a blue phosphate bead is obtained with cobalt salts: After each test.

The colourless. Titanium " Blood red when fused with a trace of iron II sulphate. Pale yellow when hot. When a silicate is strongly heated in the bead.

Vogel-Quimica Analitica Qualitativa(1aEd-1981)

Chromium Violet. Cobalt Brown. Vanadium Yellow when hot. Tungsten when cold. Yellow when hot. This reaction is employed for the detection of silicates: They accordingly adhere better to the platinum wire loop. Green when cold. Manganese Blue. In general. Grey when cold.. Colourless when hot. Copper Yellowish. Nickel Yellow. For heating moderate volumes of liquids a somewhat larger tube. Sodium carbonate bead tests the sodium carbonate bead is prepared by fusing a small quantity of sodium carbonate on a platinum wire loop in the Bunsen flame.

It is useful to remember that 10 ml of liquid fills a test-tube of this size to a depth of about 5. The intro- duction of a funnel.

Test-tubes the best size for general use is 15 x 2 cm with 25 ml total capacity. Clock glasses of the appropriate size should be provided. The majority of reactions in qualitative analysis are carried out in solution. Stirring rods a length of glass rod. A rod pointed at one end. Smaller test-tubes are sometimes used for special tests. The rods should be about 20 em long for use with test-tubes and em long for work with basins and small beakers.

Wet reactions on macro scale 2. The following general notes on basic laboratory operations should be carefully studied. Such reactions lead to: Conical or Erlenmeyer flasks these should be of Equipment 1. Open glass tubes must not be used as stirring rods. Beakers those of A test-tube brush should be available for cleaning the tubes. For evaporations and chemical reactions which are likely to become vigorous. If this is moistened. The various colours of the phosphate beads are collected in Table 2.

In most cases. A stirring rod of polythene polyethy- lene with a thin fan-shaped paddle on each end is available commercially and functions as a satisfactory 'policeman' at laboratory temperature: These flasks cannot be heated.

When set aside the walls flatten out again and air is sucked into the bottle through the tube. Polyethylene wash bottles Fig. The flow rate can easily be regulated by changing the pressure exerted by the hand. How to use H 2 S safely 7. It should always be borne in mind that a large excess of the precipitating agent may lead to the formation of complex ions and consequent partial solution of the precipitate.

Precipitation 6. Wash bottle this may consist of a ml flat-bottomed flask. Precipitation with hydrogen sulphide operations with hydrogen sulphide and sparingly are of such importance in qualitative inorganic analysis that they merit detailed discussion.

Hydrogen sulphide gas is highly poisonous. Precipitation when excess of a reagent is to be used in the formation of a precipitate.

When studying the reactions of ions the concentrations of the reagents are known and it is possible to judge the required volume of the reagent by quick mental calculation. Insulating cloth should be wound round the neck of the flask in order to protect the hand. A rubber bulb may be attached to the short tube. The pressure pushes the liquid out through the tube.

A rubber-tipped glass rod or 'policeman' is employed for removing any solid from the sides of glass vessels. As the air bubbles through the liquid.

This is usually best detected by filtering a little of the mixture and testing the filtrate with the reagent. It is recommended that the wash bottle be kept ready for use filled with hot water as it is usual to wash precipitates with hot water.

C is a stopcock which controls the flow of gas from the gen- erator. B is a wash bottle containing water and serves to remove any hydrochloric acid spray that might be carried over from the Kipp's apparatus in the gas stream. The 'bubbling' method is not recommended and should not be used for macro analysis. Passage of the gas is continued 3 Stopcock D is optional. One method. The stopper is first loosened in the neck of the flask and the gas stream turned on C first. Fortunately its unpleasant smell repels people from breathing in dangerous amounts.

In order to ensure that all the air has been expelled. With the gas flowing. The efficiency of the method is low. The conical flask is connected to the wash bottle by a short length of rubber tubing.

The most satisfactory procedure the 'pressure' method is best described with the aid of Fig. The solution is contained in a small conical flask A. Hydrogen sulphide must be handled in a fume cupboard with good ventilation. For a quantitative precipitation of sulphides e. Filtration and washing the purpose of filtration is.

The same device can be put together with glass joints. It should never be more than about two- thirds full of the solution. Filter paper pulp increases the speed of filtration by retain- ing part of the precipitate and thus preventing the clogging of the pores of the filter paper. The upper edge of the filter paper should be about 1 cm from the upper rim of the glass funnel. The best method is to add a little filter paper pulp macerated filter paper to the solution and then to filter in the normal manner.

Displacement of the gas in the flask by loosening the stopper when the bubbling has diminished considerably will ensure complete precipitation. Liquids containing precipitates should be heated before filtration except in special cases. The advantages of the 'pressure' method are: I a large surface of the liquid is presented to the gas and 2 it prevents the escape of large amounts of unused gas. This can most easily be prepared in the bottle B of the apparatus shown in Fig.

Gelatinous precipi- tates. Occa- sionally a test-tube replaces the conical flask. Such a reagent can most conveniently be used in teaching laboratories or classroom demonstrations when studying the reac- tions of ions. The delivery tube must be thoroughly cleaned after each precipitation. Filtration 8. A moderately fine-textured filter paper is generally employed. This procedure is unnecessary for 4 It must be borne in mind that the gas may contain a small proportion of hydrogen due to the iron usually present in the commercial iron II sulphide.

Washing A precipitate may be washed by decantation. Complete precipitation should be tested for by separating the precipitate by filtration. The size of the filter paper is controlled by the quantity of precipitate and not by the volume of the solution.

When a precipitate tends to pass through the filter paper. In the first. Other test papers are employed similarly. This is most readily done by pouring the solvent. The lower end of the tube or of the funnel should touch the side of the vessel in which the filtrate is being collected in order to avoid splashing. If it is desired to maintain a small volume of the liquid. If the amount of precipitate is small. For this purpose either a Whatman filter cone No.

The completion of wash- ing. The speed of filtration depends inter alia upon the length of the water column. Aids to filtration the simplest device is to use a funnel with a long stem. Removal of precipitate 9. When only a small quantity of the precipitate is available. In the second. Filtration aids and A filter flask of ml capacity is fitted with a two-holed rubber bung.

Upon applying suction to the filter paper fitted into the funnel in the usual way. To surmount the difficulty. If the solution is to be tested for acidity or alkalinity. It is frequently necessary to dissolve a precipitate completely.

The side arm of the flask is connected by means of thick-walled rubber tubing 'pressure' tubing to another flask. This is best done by directing a stream of water from a wash bottle first around the upper rim of the filter and follow- ing this down in a spiral towards the precipitate in the apex. Removal of the precipitate from the filter if the precipitate is bulky.

For many purposes a water bath a beaker half-filled with water maintained at the boiling point is quite suitable will Fig. Both types of support are folded with the filter paper to form the normal type of cone Fig. Strongly acidic or alkaline solutions cannot be filtered through ordinary filter paper.

A more convenient method. This consists of a porcelain funnel in which a perforated plate is incorporated. Evaporation Evaporation the analytical procedure may specify evaporation to a smaller volume or evaporation to dryness.

They may be filtered through a small pad of glass wool placed in the apex of a glass funnel. When filtration is complete. When the volume of liquid is small. Two thick- nesses of well-fitting filter paper cover the plate.

The Buchner funnel is fitted into the filter flask by means of a cork. The most rapid evaporation is achieved by heating the dish directly on a wire gauze. After the filter paper has been supported in the funnel. Both operations can be conveni- ently carried out in a porcelain evaporating dish or casserole. Filtration is carried out under reduced pressure exactly as with a Buchner funnel. For a large quantity of precipitate. The Jena 'slit sieve' funnel.

Vogel Quimica Analitica Qualitativa(1aEd )

The reduction in volume of a solution may also be accomplished by direct heating in a small beaker over a wire gauze or by heating in a wide test-tube 'boiling-tube'. It consists -. Should corrosive fumes be evolved during the evaporation. A useful anti-bumping device. When evaporating to dryness. A few minutes should be devoted at the end of the day's work to 'cleaning up'.

If this is not the case. Drying of precipitates partial drying. All glassware should be put away clean. A string duster is useful to wipe up liquids split upon the bench. All glass and porcelain apparatus must be scrupulously clean. The size of the Bunsen flame should be no larger than is absolutely necessary. Not wasting chemicals d Do not waste gas or chemicals.

Test-tubes may be inverted in the test-tube stand and allowed to drain. Waste disposal e Pay particular attention to the disposal of waste. Reagents should always be added portion-wise. More complete drying is obtained by placing the funnel containing the filter paper in a 'drying cone' a hollow tinned-iron cone or cylinder. Other apparatus. Remember a tidy bench is indicative of a methodical mind.

It should be extinguished when no longer required. The cleaning agent is highly corrosive! The device must not be used in solutions that contain a precipitate. Great care must be taken not to char the filter paper. The funnel is thus exposed to a current of hot air. Neither strong acids nor strong alkalis should be thrown into the sink. They should be returned to their correct places upon the shelves immediately after use. Cleanliness c When carrying out a test which depends upon the formation of a precipitate.

Cleaning of apparatus the importance of using clean apparatus cannot be too strongly stressed. Glass apparatus which appears to be particularly dirty or greasy is cleaned by soaking in chromosulphuric acid concentrated sulphuric acid containing about g of potassium dichromate per litre. A test-tube brush should be used to clean test-tubes and other glass apparatus.

Cleaning of apparatus A safer but slower method is to place the funnel and filter paper. Drying precipitates Some working hints Tidiness a Always work in a tidy. If a reagent bottle is empty. Avoid using unnecessary excess of reagents. Solids corks.

On no account may they be thrown into the sink. Taking notes g All results. The various operations occupy less time and the consumption of chemicals and glassware is reduced consider- ably.

Particular care must be directed to having both the apparatus and the work bench scrupulously clean. The writing up of experiments should not be postponed until after one has left the labora- tory. Since volumes of the order of 1 ml are dealt with. Fume cupboard f All operations involving 1 the passage of hydrogen sulphide into a solution. The sharp edges are fire-polished by heating momentarily in a flame. Various sizes are available.

These can readily be made by cutting 2 mm diameter glass rod into 12 cm lengths. In washing a precipitate with water or other liquid.

Apart from inaccuracies which may thus creep in. Semimicro operations 2. Test-tubes and centrifuge tubes small Pyrex test-tubes usually 75 x lOmm. Stirring 2. Stirring rods solutions do not mix readily in semimicro test-tubes and centrifuge tubes.

A handle may be formed. Test-tubes 1. For rapid concentration of a solution by means of a free flame. When a precipitate is to be separated by centrifuging. It is a good plan to cover these with filter paper to prevent the entrance of dust.

Before use the droppers must be calibrated. Two varieties are shown in Fig.

Hold the drop- per vertically over a clean dry 5 ml measuring cylinder. Droppers Introduce some distilled water into the clean dropper by dipping the capillary end into some distilled water in a beaker and compressing and then releasing the rubber teat or bulb. Droppers for handling liquids in semimicro analysis. Dropper b will be referred to as a capillary dropper.

The former one finds application in 30 or 60 ml reagent bottles and may therefore be called a reagent dropper. A dropping bottle of 30 ml capacity with an interchangeable glass cap Fig. It must be remembered that the volume of the drop delivered by a dropper pipette depends upon the density. The simplest containers for these corrosive liquids are 30 or 60 ml dropping bottles with glass stopper containing a groove the so-called 'TK bottle'.

A list of such reagents is given in Table 2. The bottles a and b cannot be used for concentrated acids and other corrosive liquids because of their action upon the stoppers. If the dropper delivers 20 drops of distilled water. Repeat the calibration until two results are obtained which do not differ by more than 2 drops. The standard commercial form of medicine dropper.

Count the number of drops until the meniscus reaches the 2 ml mark. This dropper is somewhat more robust than that shown in Fig. For the study of reactions it is best to divide reagents into two groups. Reagent bottles and reagents a semimicro reagent bottle may be easily constructed by inserting a reagent dropper through a cork or rubber stopper that fits a 30 or 60 ml bottle. Attach a small label to the upper part of the dropper giving the number of drops per m!. The other reagents. When using these side shelf reagents.

The dropper should deliver between 30 and 40 drops per m!. These dropping bottles Fig. Semimicro operations Calculate the volume of a single drop. Those reagents which are most frequently used should be kept by each worker separately.

M Nitric acid. The centrifuge the separation of a precipitate from a supernatant liquid is carried out with the aid of a centrifuge. This operation centrifugation replaces filtration in macro analysis. This is an apparatus for the separa- tion of two substances of different density by the application of centrifugal force which may be several times that of gravity. In practice. If accidental contact should be made. IBM Sulphuric acid. Under no circumstances should the capillary end of the dropper be dipped into any foreign solution.

The supernatant Table 2. The tube and its contents. Centrifuge 5. The hand-driven centrifuge is inexpensive and is satisfactory in most cases. In the latter case.. A small 2-tube hand centrifuge with protecting bowl and cover Fig. An inexpensive constant speed. Several types of centrifuge are available for semimicro analysis. The buckets can either 'swing out' to the horizontal position or. The advantages of centrifugation are: The central spindle should be provided with a locking screw or nut: Spilling may corrode the buckets and produce an unbalanced head..

O i l here Fig. These are: If a suspicious sound is heard. Most semimicro centrifuges will accommodate both semimicro test-tubes 75 x 10 mm and centrifuge tubes up to 5 ml capacity.

As the pressure is very slowly released the liquid rises in the dropper and the latter is lowered further into the liquid An unusual sound may be due to the breaking of a tube. The advantages of the latter include easier removal of the mother liquor with a dropper. Agitate the surface with a stirring rod if necessary. Do not attempt to retard the speed of the centrifuge with the hand.

Fix the cover in place. Surface tension effects prevent surface particles from settling readily. Maintain the maximum speed for seconds. Separation of solid and To remove the supernatant liquid. It is of the utmost importance to avoid strains or vibrations as these may result in stirring up the mixture and may damage the apparatus. A little practice will enable one to judge the exact time required to pack the precipitate tightly at the bottom of the tube. Washing 6.

Washing the precipitates it is essential to wash all precipitates in order to remove the small amount of solution present in the precipitate.. In difficult cases. The solution in the dropper should be perfectly clear. Great care should be taken as the capillary approaches the bottom of the centrifuge tube that its tip does not touch the precipitate The wash liquid is usually water..

The wash liquid is a solvent which does not dissolve the precipitate but dilutes the quantity of mother liquor adhering to it. It is best to wash the precipitate at least twice. Wash bottles For those who prefer wash bottles. The supernatant liquid is removed by a capillary dropper..

This operation is usually difficult Transferring of precipitates in some cases precipitates can be transferred from semimicro test-tubes with a small spatula two convenient types in nickel or monel metal are shown in Fig.

Wash bottles for most work in semimicro analysis a 30 or 60ml glass stoppered bottle is a suitable container for distilled water A small conical flask 25 or 50 m! The danger of 'bumping' may be considerably reduced by employing the anti- bumping device shown in Fig. The test-tube may be washed by holding it in an almost vertical upside down position with its mouth over the receptacle and directing a fine stream of solution or water from a capillary dropper onto the sides of the test-tube.

The 'bumping' or spattering of hot solutions may often be dangerous and lead to serious burns if the solution contains strong acids or bases. It is a good plan to wind a thin rubber band about 5 mm from the top of Fig. Heating of solutions solutions in semimicro centrifuge tubes cannot be heated over a free flame owing to the serious danger of 'bumping' and con- sequent loss of part or all of the liquid in such narrow tubes.

If the precipitate in a test-tube is to be treated with a reagent in an evaporating dish or crucible. Heating solutions 9.

This may consist of a ml Pyrex beaker. The simplest procedure is to employ a small water bath. The latter heating operation requires very careful manipulation and should not be attempted by beginners.

The mouth of the test-tube must be pointed away from others nearby. Similar remarks apply to semimicro test-tubes. Water bath On the whole it is better to resort to safer methods of heating.

Evaporations where rapid concentration of a liquid is required or where volatile gases must be expelled rapidly. A more elaborate arrangement which will.. I Fig. The apparatus is constructed of monel metal. This rack will accommodate four centrifuge tubes and four semimicro test-tubes. The dimensions of a rack of smaller size are given in Fig. Useful holders. Evaporation to dryness may also be accomplished by direct intermittent heating with a micro burner of a crucible supported on a nichrome or silica triangle or of a semimicro beaker supported on a wire gauze.

In later chapters. If corrosive fumes are evolved. This may be placed in an air bath consisting of a 30 ml nickel crucible and supported thereon by a ring Fig. Dissolving of precipitates the reagent is added and the suspension is warmed. A little practice is required in order to achieve regular boiling by intermittent heating with a flame and also to avoid 'bumping' and spattering.

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