Environment Igcse Chemistry Book Pdf


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Cambridge IGCSE Chemistry, Fourth edition Coursebook with CD-ROM Richard This book thoroughly covers the Cambridge International Examinations (CIE). You must not circulate this book in any other binding or cover and you must impose this If you are taking IGCSE chemistry, using the Cambridge International. Cambridge. IGCSE® Chemistry. Practice Book. Answers. 1 All about matter. 1 (a) A condensation, B boiling, C freezing, D melting, E sublimation [1 for each].

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are taking IGCSE chemistry, using the Cambridge International revision, sample Computer hardware and software brand names mentioned in this book are. If you are taking IGCSE chemistry, using the Cambridge International. Examinations syllabus , then this book is for you. It covers the syllabus fully, and has. awarded and/or comments that appear in this book/CD were written by the authors. Questions from the Cambridge IGCSE Chemistry papers are reproduced.

The Coursebook has been revised ensuring that it is up to date and comprehensive in its coverage with supplementary material clearly marked. The Coursebook contains: We enable thousands of students to pass their Cambridge exams by providing comprehensive, high-quality, endorsed resources. It is endorsed by Cambridge International Examinations for use with their examination. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published Second edition Third edition Fourth edition Printed in the United Kingdom by xxxxxxx xxxxxxxxxx xxxxxxxxxx A catalogue record for this publication is available from the British Library Library of Congress Cataloguing in Publication data. Information regarding prices, travel timetables, and other factual information given in this work is correct at the time of first printing but Cambridge University Press does not guarantee the accuracy of such information thereafter.

The problem we face is balancing the amount of carbon dioxide being added to the atmosphere with the amount being taken out by plants and the oceans Figure 1. The nitrogen cycle Nitrogen is essential for plant growth and therefore for the life of animals Figure 1. Plants generally get their nitrogen from nitrates in the soil and animals get theirs from eating plants. This process is called nitrogen fixation. During thunderstorms, the very high temperature of the lightning provides enough energy to cause atmospheric nitrogen and oxygen to react with water in the atmosphere to form nitric acid.

When this falls with rain, it forms nitrates in the soil. Nitrogen is also taken from the air by the chemical industry when fertiliser is made by the Haber process. Taken together, these processes form the nitrogen cycle Figure 1. These three major cycles — of water, carbon and nitrogen — together with the rock cycle interlink and, between them, provide us with the resources we need.

In human terms, resources are materials we get from the environment to meet our needs. Some are the basic material resources we and other organisms need to keep alive; others are materials from which we obtain energy, or substances useful for our civilised way of life.

Chemistry helps us to understand how the basic resources sustain our life. It also provides the methods of extraction and use of other resources. When plants and animals die and decay, bacteria help the decomposition and nitrogen is returned to the soil. There are also bacteria that live in the roots of some plants e.

Material resources can be broadly subdivided into renewable, potentially renewable and non-renewable resources, based on our short human timescale. They were formed over millions of years and are being used up much faster than they are being formed. Renewable resources are those that essentially will never run out are inexhaustible — for example, wind, tides and direct solar energy.

Potentially renewable resources can be renewed, but they will run out if we use them more quickly than they can be renewed. Examples include fresh water and air, fertile soil, and plant and animal biomass. The biggest environmental concern is the depletion of non-renewable resources.

Once they are used up, we will have to manage without them. Metal ores, especially those of iron, aluminium and copper, are becoming scarcer. The ores that still exist are often of low quality, making the process of extraction costly.

Fossil fuels are another concern. New deposits of oil are being discovered but the speed at which we are using the oil we have is increasing. A time will come when all the oil, and eventually all the coal, will run out. Phosphate minerals, essential for the manufacture of fertilisers, are also becoming scarcer. A number of these problems can be reduced by recycling some of the substances we use: All recycling helps save energy, which comes mainly from fossil fuels. Fossil fuels are a bigger problem.

We will always need energy. A partial solution is to make more use of our renewable resources. Wind power, solar power and water power from rivers, tides and waves can all be used to generate electricity. An increasing problem is the way in which our potentially renewable resources are being affected by overuse and pollution.

Complete Chemistry for Cambridge IGCSE

The next three sections give more detail on these problems. Questions 1. Carbon dioxide is an important part of the air but makes up only about 0.

The carbon dioxide which is used by humans is not usually obtained from the air. Nitrogen is used in the manufacture of ammonia and fertilisers in the Haber process. Liquid nitrogen is used in cryogenics the storing of embryos and other types of living tissue at very low temperatures. Nitrogen is also sometimes used where an unreactive gas is needed to keep air away from certain products; for example, it is used to fill bags of crisps chips to ensure that the crisps do not get crushed or go rancid as a result of contact with oxygen in the air.

The biggest single use of oxygen is in the production of steel from cast iron. It is also used in oxyacetylene torches to produce the high-temperature flames needed to cut and weld metals. In hospitals, oxygen in cylinders is used to help the breathing of sick people. Activity 1. You need to give a use of pure oxygen. Before any of the gases in the air can be used separately, they have to be separated from the air in the atmosphere.

The method used is fractional distillation, which works because the gases have different boiling points Table 1. Studyy tip p Argon and other noble gases are used in different types of lighting. It does not react with tungsten even at very high temperatures. The other noble gases are used in advertising signs 6. Figure 1. The process of fractional distillation involves two stages. The various gases boil off one at a time at different temperatures.

Pollution of the air Many gases are accidentally or deliberately released into the air. Some are harmless but many create problems for the environment.

Most countries produce electricity by burning coal or oil. Both these fuels are contaminated with sulfur, which produces sulfur dioxide when it burns: Oxides of nitrogen NOx for example, nitrogen dioxide, NO2 are also produced when air is heated in furnaces.

There are numerous effects of acid rain. Trees are deprived of these nutrients. Aluminium ions are freed from clays as aluminium sulfate, which damages tree roots. The tree is unable to draw up enough water through the damaged roots, and it dies. The wind can carry acid rain clouds away from the industrialised areas, causing the pollution to fall on other countries. One way to remedy the effects of acid rain is to add lime to lakes and the surrounding land to decrease the acidity.

The best solution, however, is to prevent. In these devices, the acidic gases are passed through an alkaline substance such as lime. This removes the acids, making the escaping gases much less harmful. In many countries, though, acidic gases from power stations are still a serious problem. Petrol gasoline and diesel for use in road transport have most of their sulfur removed when they are refined. Sulfur dioxide is not a serious problem with motor vehicles but the other contents of vehicle exhaust fumes Figure 1.

Nitrogen dioxide, for example, is still produced. Because of the lack of oxygen in the enclosed space of an engine, the fuel does not usually burn completely and carbon monoxide CO is formed. Another pollution problem arising from motor vehicles is caused by tetraethyl lead in petrol leaded petrol. Burning this type of petrol releases the toxic metal lead into the environment Figure 1. The use of lead in petrol has decreased significantly over the last 20 years.

In , the United Nations announced the successful, worldwide, phasing out of leaded petrol for road vehicles. There are only a handful of countries where it is still available. The dangers of these pollutants are as follows. This contains low-level ozone and is likely to cause breathing problems, especially in people with asthma.

It combines with the haemoglobin in blood and stops it from carrying oxygen. Even very small amounts of carbon monoxide can cause dizziness and headaches.

Larger quantities cause death. The body cannot easily get rid of lead, so small amounts can build up to dangerous levels over time. There are solutions to some of these problems.

Catalytic converters can be attached to the exhaust systems of cars Figure 1. These convert carbon monoxide and nitrogen dioxide into carbon dioxide and nitrogen. Unfortunately, if there is lead in the petrol being used, the catalyst becomes poisoned and will no longer work.

This means that in countries. Studyy tip p Try to keep these different atmospheric pollution problems clear and distinct in your mind rather than letting them merge together into one confused? They each have distinct causes and clear consequences.

The Earth is warmed by the Sun but this heat would quickly escape if it were not for our atmosphere.

It is always colder on a clear night because there are no clouds to keep the heat in. Some gases are better at keeping heat in than others; if there is too much of these gases in the atmosphere, the Earth gets warmer and this causes problems Figure 1.

Some energy is radiated back into space as light and heat. The Earth warms up. Some of the problems global warming will cause are listed below. This will cause a rise in sea level, and low-lying land will be flooded.

Deserts will spread and millions of people will have less water. Carbon dioxide and methane are the two main problem gases; methane is around 20 times more effective at stopping heat escaping than carbon dioxide is.

Carbon dioxide enters the air through respiration and burning and it is removed by plants during photosynthesis. Burning more fuel and cutting down the forests increase the problem. Burning less fossil fuel and planting more trees would help to solve it. Methane is produced by animals such as cows: It emerges from both ends of the cow but mostly from the mouth.

Intriguingly, termites are also significant contributors to the methane in the atmosphere Figure 1. In addition, it is produced by the decay of food and other dead organic matter.

It is produced in large quantities by rice paddy fields Figure 1. Treating a. Melting of the Arctic ice and the consequent release of the large amount of the gas stored in the permafrost could have a huge economic and damaging environmental impact.

The water purification process is designed to remove the last two of these. At its simplest, water treatment involves filtering the water to remove solid particles and adding chlorine to kill any bacteria that could cause disease.

The main difference from the simple treatment is in the use of ozone to remove pesticides and some other dissolved substances which can cause health problems. The water is still not totally pure as it contains some dissolved solids. Some of these, such as calcium salts, can aid health, whereas others, such as nitrate fertilisers, can be harmful.

In some parts of the world, seawater is made drinkable by desalination taking the salt out. This can be done by distillation or by forcing the water through special membranes using high pressures reverse osmosis. Desalination is particularly important in countries such as Saudi Arabia. Our water supply is very important. Not only is it used in the home, as shown in Figure 1. Most of the water used by industry is utilised as a solvent for other substances, to cool down reactions or to transfer heat from one part of a factory to another.

There is plenty of water on the Earth but most of it is in seas and oceans and the salts dissolved in it make it unsuitable for many uses. You will see from the diagram that less than a teaspoon of water out of every dm3 is easily available for human use. This would be enough but it is not equally distributed around the world: Water is essential to life but it can also carry disease.

Polluted water kills many millions of people every year. It is important that the water we drink is treated to make it safe, and even more important that sewage human and animal waste is treated before being allowed back into rivers used for drinking water. Water treatment Water from rivers and lakes, and from underground, can contain dissolved salts, solid particles and bacteria.

Wear eye protection throughout. Take care with hot apparatus and solutions. The sea is mainly water but there are lots of other things in it too. The most common substance in seawater is sodium chloride, or common salt. Other substances in it include calcium sulfate, magnesium sulfate and tiny amounts of metals such as copper and iron.

Solid will be precipitated during this evaporation process. This will occur when about 30—40 cm3 of liquid remains. The role of the oceans in the carbon cycle: In each case, time how long it takes the indicator to become yellow.

Record the results. Questions A1 What evidence is there that seawater is a mixture of salts? A2 What gas is likely to have been given off when hydrochloric acid is added to the solids first collected?

A3 What does this tell you about the identity of these solids? A4 Search the internet to try to find information about the solubilities of sodium chloride and calcium sulfate — two common compounds present in seawater. Use this information to predict the possible identity of the final solid left at the end of your experiment. The numbers show how much water is used on average per person for each activity every day.

Industry sometimes discharges toxic and harmful substances into rivers. Release of untreated sewage into rivers can lower oxygen levels by chemical reaction and cause the spread of harmful bacteria, increasing the risk of disease. Warm water can dissolve less oxygen than cold water, so animals living in the water may be left with insufficient oxygen.

All of these, and others, lead to problems in rivers and lakes. Questions Pollution of the water supply Issues concerning the pollution of water include the following: These nitrates are not removed by water treatment and can cause health problems for old people and for young children. This rock is changed and sometimes decomposed before it rises back to the surface and cools. These processes give rise to different types of rock and we extract some of those near the surface by mining and quarrying for human use.

The crust varies in thickness from 5 km below some parts of the ocean to around 50 km in some parts of the land mass. The crust is where the majority of the chemicals that we use come from. Metal ores are rocks that have a relatively high concentration of a mineral containing a certain metal. For more details of ores and methods of obtaining metals from them, see Chapters 8 and 9. Rocks can be used for building and for the extraction of useful chemicals other than metals.

The most useful of these is limestone. Limestone is an important resource from which a useful range of compounds can be made. The reactions involved in producing these compounds can be imitated in the laboratory Figure 1. The piece of lime is allowed to cool and then a few drops of water are added. This reaction is strongly exothermic. If more water is added, an alkaline solution limewater is obtained. The cycle can be completed by bubbling carbon dioxide into the solution.

A white precipitate of calcium carbonate is formed. More detail on the importance of limestone and the chemicals derived from it can be found in Section 9.

This includes the method of making lime industrially. The problem of fossil fuels The major fossil fuels are coal, petroleum or crude oil and natural gas. These are important sources of energy but are also very important as sources of raw materials for making plastics, drugs, detergents and.

For more detail of fossil fuels and their uses see Chapter They are, however, mostly used as fuels and they are a limited, non-renewable resource. In , it was estimated that the fossil fuel supplies we currently know about would last a further 43 years.

Hydrogen as a fuel Hydrogen gas has attractions as a fuel. All it produces on burning is water. When hydrogen burns, it produces more energy per gram than any other fuel Figure 1. The gas itself is difficult to store and transport because of its low density. The first vehicles to run on hydrogen were the rockets of the US space programme. Hydrogen is not cheap. The main method of obtaining it on a large scale is by the electrolysis of water.

However, this is not very economical. It is possible that cheap surplus electricity from nuclear power may make electrolysis more economical. Others have suggested the use of electricity from solar power.

Despite these difficulties, prototype hydrogenpowered cars have been tried. The Japanese prototype burns the hydrogen in the engine, while the German—Swiss—British venture uses the hydrogen in a fuel cell.

Electricity from this cell then powers an electric motor Figure 1.

Using a fuel cell operating an electric motor, hydrogen has an. Hydrogen is one possible fuel for the future, either as a substance to burn or for use in fuel cells. As more countries become industrialised, energy use in the world is increasing at an even faster rate than the population. Table 1. The figures show how relatively little energy is obtained from sources other than fossil fuels, with the figure for coal showing a notable increase between and Hydroelectric power 6.

In , only 1. Clearly change is necessary Figure 1. The Sun is the greatest provider of energy to the Earth. Hydrogen produces more energy per gram than any other fuel.

Groups of students are to design a flyer, leaflet or web page to be used as publicity by a car dealership outlining the issues and benefits of hydrogen-powered cars. Use the internet to find information.

In this mode, the cell acts as an electrolyser and can decompose distilled water into its elements. The experiment can then be reversed and the gases collected can be used to power the fuel cell to drive a small electric fan. The car is powered by electrons released at the negative electrode. Inside the fuel cell, hydrogen ions move to the positive electrode, where they react with oxygen to form water.

Hydrogen fuel cells Research has found a much more efficient way of changing chemical energy into electrical energy by.

A hydrogen fuel cell can be used to power a car. Such a cell operates continuously, with no need for recharging. The cell supplies energy as long as the reactants are fed in to the electrodes. The overall reaction of the hydrogen—oxygen fuel cell is: Land pollution Cities throughout the world are covered in litter. Some make an effort to control it but it is always there.

Most of our waste material is buried and this can lead to problems. Toxic and radioactive waste can make the land unusable and many countries strictly control what can be buried and where. Companies are required, by law, to treat their waste products to make them as harmless as possible.

Domestic waste should be recycled whenever possible. Waste that cannot be treated in this way should be burned to create energy. If it is left in landfill sites, it.

Methane is much more harmful to the environment than the carbon dioxide produced by burning it, as methane is a more powerful greenhouse gas. Give the word and balanced chemical equations for the reaction.

You should know: The water cycle and the carbon cycle are both of vital importance to life. Explain how they both depend on energy from the Sun. Water is present in the atmosphere, in the seas and in ice and snow. Give the test and the positive result. What do you understand by the term solvent? Describe two of the steps in water purification.

For each of these steps, give an explanation of its purpose. State the percentage of oxygen present in the air. Explain your choice. Describe how water is treated before it enters the water supply.

Two important greenhouse gases are methane and carbon dioxide. The methane in the atmosphere comes from both natural and industrial sources. What are the products of this oxidation? Give an example of bond breaking in the above reaction. Give an example of bond forming in the above reaction. Is the change given in part i exothermic or endothermic? Give two reasons why hydrogen may be considered to be the ideal fuel for the future.

Suggest a reason why hydrogen is not widely used at the moment. The diagram shows part of the carbon cycle. This includes some of the processes that determine the percentage of carbon dioxide in the atmosphere. Name another one. Suggest an explanation for this increase. Lord of the rings Saturn is perhaps the most beautiful of the planets of the Solar System. It has fascinated astronomers because of its mysterious rings Figure 2. The Pioneer, Voyager and Cassini—Huygens space-probes sent back a great deal of information on the nature of the rings and the mass of Saturn itself.

Each ring is made up of a stream of icy particles, following each other nose-to-tail around. Figure 2. The rings are made of ice and dust. The particles can be of widely varying sizes. The rings resemble a snowstorm, in which tiny snowflakes are mixed with snowballs up to the size of a house. Deep in the centre of these lightweight gases is a small rocky core, surrounded by a liquid layer of the gases.

The hydrogen is liquid because of the high pressure in the inner regions of the planet nearest the core. The liquid hydrogen behaves with metallic properties. How do changing conditions affect the appearance, properties and behaviour of different substances? The word is used to cover all the substances and materials of which the Universe is composed. Samples of all of these materials have two properties in common: Chemistry is the study of how matter behaves, and of how one kind of substance can be changed into another.

Whichever chemical substance we study, we find it can exist in three different forms or physical states depending on the conditions. These three different states of matter are known as solid, liquid and gas.

The different physical states have certain general characteristics that are true whatever chemical substance is being considered. There are three physical states: The three physical states show differences in the way they respond to changes in temperature and pressure. All three show an increase in volume an expansion when the temperature is increased, and a decrease in volume a contraction when the temperature is lowered.

The effect is much bigger for a gas than for either a solid or a liquid. The volume of a gas at a fixed temperature can easily be reduced by increasing the pressure on the gas.

Liquids, on the other hand, are only slightly compressible, and the volume of a solid is unaffected by changing the pressure. Changes in physical state Large changes in temperature and pressure can cause changes that are more dramatic than expansion or contraction. They can cause a substance to change its physical state.

The changes between the three states of matter are shown in Figure 2. At atmospheric pressure, these changes can be brought about by raising or lowering the temperature of the substance. Melting and freezing The temperature at which a pure substance turns to a liquid is called the melting point m. This always happens at one particular temperature for each pure substance Figure 2.

The process is reversed at precisely the same temperature if a liquid is cooled down. It is then called the freezing point f. The melting point and freezing point of any given substance are both the same temperature. Gallium is a metal that has a melting point just above room temperature. Instead, they turn directly into gas.

This change of state is called sublimation: Like melting, this also happens at one particular temperature for each pure solid. Iodine is another solid that sublimes. It produces. Evaporation and condensation take place over a range of temperatures; boiling takes place at a specific temperature. Evaporation, boiling and condensation If a liquid is left with its surface exposed to the air, it evaporates.

Splashes of water evaporate at room temperature. After rain, puddles dry up! When liquids change into gases in this way, the process is called evaporation. Evaporation takes place from the surface of the liquid.

The larger the surface area, the faster the liquid evaporates. It will literally melt in the hand. The warmer the liquid is, the faster it evaporates. Eventually, at a certain temperature, it becomes hot enough for gas to form within the liquid and not just at the surface.

Bubbles of gas appear inside the liquid. This process is. If the surrounding pressure is increased, the boiling point rises. On warming, it produces a purple vapour which then condenses again on the cool part of the tube.

It takes place at a specific temperature, known as the boiling point b. Water evaporates fairly easily and has a relatively low boiling point — it is quite a volatile liquid. It has a higher volatility than water.

A volatile liquid is one which evaporates easily and has a relatively low boiling point. Ethanol b. The reverse of evaporation is condensation. This is usually brought about by cooling. However, we saw earlier that the gas state is the one most affected by changes in pressure.

It is possible, at normal temperatures, to condense a gas into a liquid by increasing the pressure, without cooling. The boiling point of a liquid can change if the surrounding pressure changes.

The value given for the boiling point is usually stated at the pressure of the atmosphere at sea level atmospheric pressure or standard pressure. If the surrounding pressure falls, A pure substance consists of only one substance. There is nothing else in it: A pure substance melts and boils at definite temperatures. Table 2. The values for the melting point and boiling point of a pure substance are precise and predictable.

This means that we can use them to test the purity of a sample. They can also be used to check the identity of an unknown substance. The melting point can be measured using an electrically heated melting-point apparatus Figure 2. The melting is viewed through a magnifying lens. An impure substance sometimes melts or boils over a range of temperatures, not at a particular point. The presence of an impurity in a substance: Study tip Remember that pure substances have definite, sharp melting and boiling points.

The presence of an impurity means that these changes will be spread over a range of temperatures in each case. For example, if the m. These are quite common questions. Heating and cooling curves The melting point of a solid can also be measured using the apparatus shown in Figure 2.

A powdered solid is put in a narrow melting-point tube so that it can be heated easily.

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We can follow the temperature of the sample before and after melting. Similar apparatus can be used to produce a heating curve but the thermometer must be placed in a test tube containing the solid being studied. The effect of impurities Seawater is impure water.

You can show this if you put some seawater in an evaporating dish and boil away the water, because a solid residue of salt is left behind in the dish. Other impure substances show similar differences. These experiments show that heat energy is needed to change a solid into a liquid, or a liquid into a gas. During the reverse processes, heat energy is given out. When a solid is melted, or a liquid is boiled, the temperature stays constant until the process is complete.

The same is true in reverse when a gas condenses or a liquid freezes. Notice that, while the solid is melting, the temperature stops rising. It will only begin to rise again when all the naphthalene has melted. Generally, the heating curve for a pure solid stops rising at its melting point. The heating curve for wax, which is a mixture of substances, shows the solid wax melting over a range of temperatures.

It is possible to heat a liquid in the same apparatus until its boiling point is reached. Again, the temperature stays the same until all the liquid has boiled.

The reverse processes can be shown if a sample of gas is allowed to cool. This produces a cooling curve Figure 2. The level portions of the curve occur. The temperature stays constant while the gas condenses, and while the liquid freezes.

In this experiment, you will plot cooling curves for two different substances. Adaptations of this experiment and details of the use of it in assessing practical skills AO3. Types of mixture Our world is very complex, owing to the vast range of pure substances available and to the variety of ways in which these pure substances can mix with each other.

Water would be rather tasteless if we drank it pure distilled. Each mixture must be made from at least two parts, which may be solid, liquid or gas. There are a number of different ways in which the three states can be combined. Technically, the term solution is used for this type of mixture. Solid salt dissolves in liquid water to produce a liquid mixture — a salt solution Figure 2.

The liquid in which the solid dissolves is called the solvent. In other types of mixture, the states remain separate.

One phase is. Perhaps the most obvious example of this type of mixture is a suspension of fine particles of a solid in a liquid, such as we often get after a precipitation reaction. Solutions There are various ways in which substances in different states can combine.

Perhaps the most important idea here is that of one substance dissolving in another — the idea of a solution.

We most often think of a solution as being made of a solid dissolved in a liquid. The salts are totally dispersed in the water and cannot be seen.

However, other substances that are not normally solid are dissolved in seawater. For example, the dissolved gases, oxygen and carbon dioxide, are important for life to exist in the oceans.

Less obvious perhaps, but quite common, are solutions of one liquid in another. Alcohol mixes dissolves completely with water. Beer, wine and whisky do not separate out into layers of alcohol and water even when the alcohol content is quite high.

Alcohol and water are completely miscible: Alloys are similar mixtures of metals, though we do not usually call them solutions. They are made by mixing the liquid metals together dissolving one metal in the other before solidifying the alloy.

Being able to purify and identify the many substances present in these mixtures not only satisfies our curiosity but is crucial to our well-being and health.

There is a range of physical techniques available to make the necessary separations Table 2. They all depend in some way on a difference in the physical properties of the substances in the mixture.

The most useful separation method for a particular mixture depends on: Separating insoluble solids from liquids In some ways these are the easiest mixtures to separate.

Quite often, just leaving a suspension of a solid in a liquid to stand achieves a separation — especially if the particles of solid are large enough. Once the solid has.

A vacuum pump is connected to the side-arm flask; it speeds up the flow of liquid through the funnel. A more generally useful method for separating solids from liquids is filtration Figure 2. Here the insoluble material is collected as a residue on filter paper. Filtration is useful because both phases can be obtained in one process. The liquid phase is collected as the filtrate.

Various large-scale filtration methods are used in industry. Perhaps the most useful of these are the filter beds used to treat water for household use. Another method of separating an insoluble solid from a liquid is centrifugation where the mixture is spun at high speed in a centrifuge. This causes the solid to be deposited at the bottom of the centrifuge tube.

The liquid can be carefully decanted off.

Separating immiscible liquids Mixtures of two immiscible liquids can be separated if the mixture is placed in a separating funnel and allowed to stand. The liquids separate into different layers. This type of separation is For example, at the base of the blast furnace the molten slag forms a separate layer on top of the liquid iron.

Separating mixtures of solids The separation of a solid from a mixture of solids depends largely on the particular substance being purified. Some suitable difference in physical properties needs to be found. Usually it helps if the mixture is ground to a powder before any separation is attempted. These methods depend on the gold dust being denser than the other substances in the river sediment.

This type of method is also used in purifying the ores of zinc and copper, although in these cases the metals are less dense than the ores and so float on the surface. Separations based on magnetic properties Magnetic iron ore can be separated from other material in the crushed ore by using an electromagnet. In the Amazonian gold diggings, magnets are used to clean away iron-containing, red-brown dust from the powdered gold. In the environmentally and economically important processes of recycling metals, iron objects can be picked out from other scrap metal using electromagnets.

The mixture in the solvent is then warmed and stirred. Care must be taken at the warming stage when using solvents other than water. The warm mixture is then filtered Figure 2. This leaves the insoluble substances as a residue on the filter paper, which can be dried. The soluble substance is in the liquid filtrate. Dry crystals can be obtained by evaporation and crystallisation, see Figure 2. Separations based on sublimation A solid that sublimes can be separated from others using this property Figure 2.

The aim of this activity is to separate a mixture of salt and sand. The method uses the difference in solubility of the two solids and the technique of filtration. Separations based on differences in solubility One very useful way of separating a soluble substance from a solid mixture is as follows. The mixture is first ground to a powder. A suitable liquid solvent is added. The solvent must dissolve one of the solid substances present, but not the others. The solvent is often water,. The crystals condense on the cooled surface.

While the solvent is evaporating, dip a glass rod into the solution from time to time. When small crystals form on the rod, take the solution off the water bath and leave it to cool. This method should not be used if the solvent is flammable.

Instead, use an electrical heating element and an oil or water bath. Separating solutions The separation of this type of mixture is often slightly more complicated because there is no physical separation of the phases in the original mixture. The methods of separation usually depend on solubility properties or on differences in boiling point or volatility. Separating a solid from solution in a liquid can be carried out by evaporation or crystallisation.

Evaporation gives only a powder, but crystallisation can result in proper crystals. Both processes begin by evaporating away the liquid but, when crystals are needed, evaporation is stopped when the solution has been concentrated enough.

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The concentrated solution is allowed to cool slowly. The crystals formed can then be filtered off and dried. Separating a liquid from a solution is usually carried out by distillation Figure 2.

The boiling point of. The liquid is more volatile than the dissolved solid and can easily be evaporated off in a distillation flask. It is condensed by passing it down a water-cooled condenser, and then collected as the distillate. Separating the liquids from a mixture of two or more miscible liquids is again based on the fact that the liquids will have different boiling points.

However, the boiling points are closer together than for a solid-inliquid solution and fractional distillation must be used Figure 2. When a mixture of the two is heated, ethanol and water vapours enter the fractionating column.

Glass beads in the column provide a large surface area for condensation Figure 2. Evaporation and condensation take place many times as the vapours rise up the column.

Ethanol passes through the condenser first as the temperature of the column is raised above its boiling point.

By watching the temperature carefully, the two liquids fractions can be collected separately. Fractional distillation is used to separate any solution containing liquids with different boiling points. The liquid in the mixture with the lowest boiling point the most volatile distils over first.

The final liquid to distil over is the one with the highest boiling point the least volatile. Fractional distillation can be adapted as a continuous process and is used industrially to separate: Study tip In fractional distillation remember that it is the liquid with the lowest boiling point that distils over first.

Separating two or more dissolved solids in solution can be carried out by chromatography. There are several types of chromatography, but they all follow the same basic principles.

Paper chromatography is probably the simplest form to set up and is very useful if we want to analyse the substances present in a solution. For example, it can tell us whether a solution has become contaminated. This can be very important because contamination of food or drinking water, for instance, may be dangerous to our health. A drop of concentrated solution is usually placed on a pencil line near the bottom edge of a strip of chromatography paper.

The paper is then dipped in the solvent. The level of the solvent must start below the sample. Many different solvents are used in chromatography. Water and organic solvents carbon-containing solvents such as ethanol, ethanoic acid solution and propanone are common. Organic solvents are useful because they dissolve many substances that are insoluble in water. When an organic solvent is used, the process is carried out in a tank with a lid to stop the solvent evaporating.

Activity 2. These food colours are used in cake making, for instance, and there is quite a wide range of permitted colours readily available. The substances separate according to their solubility in the solvent. As the solvent moves up the paper, the substances are carried with it and begin to separate.

The substance that is most soluble moves fastest up the paper. An insoluble substance would remain at the origin. The run is stopped just before the solvent front reaches the top of the paper. The original spot is identified as A.

The sample is separated as it moves up the paper. The distance moved by a particular spot is measured and related to the position of the solvent front. The ratio of these distances is called the Rf value, or retention factor. This value is used to identify the substance: Originally, paper chromatography was used to separate solutions of coloured substances dyes and pigments since they could be seen as they moved up the paper.

However, the usefulness of chromatography has been greatly increased by the use of locating agents Figure 2. These mean that the method can also be used for separating substances that are not coloured. The paper is treated with locating agent after the chromatography run.

The agent reacts with the samples to produce coloured spots. Chromatography has proved very useful in the analysis of biologically important molecules such as sugars, amino acids and nucleotide bases. The purity and identity of substances Paper chromatography is one test that can be used to check for the purity of a substance.

If the sample is pure, it should only give one spot when run in several different solvents. The identity of the sample can also be checked by comparing its Rf value to that of a sample we know to be pure. Probably the most generally used tests for purity are measurements of melting point or boiling point. As we saw earlier, impurities would lower the melting point or raise the boiling point of the substance.

They would also make these temperatures less precise. These temperatures have been measured for a very wide range of substances.

The identity of an unknown substance can be found by checking against these measured values for known pure substances. The process of purification is of crucial importance in many areas of the chemical industry. Medicinal drugs pharmaceuticals must be of the highest possible purity. Any contaminating substances, even in very small amounts, may have harmful side effects. Coloured dyes food colourings are added to food and drinks to improve their appearance. The colourings added need to be carefully controlled.

In Europe the. Chromatography using a locating agent to detect the spots on the paper. Alternatively, the locating agent can be sprayed on the paper. Many dyes that were once added are now banned.

Even those which are permitted may still cause problems for some people. The yellow colouring tartrazine E is found in many drinks, sauces, sweets and snacks. To most people it is harmless, but in some children it appears to cause hyperactivity and allergic reactions, for example asthma.

Even where there is overall government regulation, individuals need to be aware of how particular foods affect them. A closer look at solutions The solubility of solids in liquids Probably the most important and common examples of mixtures are solutions of solids in liquids.

Water is the commonest solvent in use, but other liquids are also important. Most of these other solvents are organic liquids, such as ethanol, propanone and trichloroethane.

These organic solvents are important because they will often dissolve substances that do not dissolve in water. If a substance dissolves in a solvent, it is said to be soluble: If we try to dissolve a substance such as copper ii sulfate in a fixed volume of water, the solution. The concentration of a solution is the mass of solute dissolved in a particular volume of solvent, usually 1 dm3.

If we keep adding more solid, a point is reached when no more will dissolve at that temperature. This is a saturated solution. To get more solid to dissolve, the temperature must be increased. The concentration of solute in a saturated solution is the solubility of the solute at that temperature.

The solubility of most solids increases with temperature. The process of crystallisation depends on these observations. May I have the book in my email please, aust. Please follow these instructions to download this book. By any chances, do u have the pdf of the complete igcse chemistry of cambridge igcse 2nd edition of the CD answers that contains core curriculum answer? Please follow these download instructions. It is not downloading.

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