Chemistry Lower School Textbook

Lower School Chemistry

NES/Chemistry Year 7 Chemistry A Gru and Minion production. 1

NES/Chemistry Contents Topic 1 – Safety and Apparatus ................................................................3 Safety & Hazards Apparatus Measuring Topic 2 – Scientific Method ........................................................................16 The Scientific Method Variables Planning your own Experiment Topic 3 – States of Matter ........................................................................21 Solids, Liquids and Gases Colloids Physicals Properties of Materials Topic 4 – Physical Changes ........................................................................26 Changes of State Heating and Cooling Curves Diffusion Topic 5 – Mixtures ..................................................................................36 Purity Solutions Air Topic 6 – Separation Techniques ..............................................................43 Decanting and Filtration Evaporation Distillation Separating Funnel Chromatography Topic 7 – Atoms .............................................................................................51 Atomic Structure Atomic Number and Mass Number Isotopes Electronic Configuration and Valence Electrons 2

NES/Chemistry Topic 1 – Safety, Apparatus and Measuring This topic is split up into the following parts: 1. Safety 2. Using apparatus 3. Taking measurements during experiments Definitions Explosive Substances which may explode if heated, exposed to a flame, or knocked. Toxic Substances which may cause death by poisoning. Flammable Substances which may catch fire easily. Corrosive Substances which can burn and destroy living tissue. Harmful Substances which represent a moderate risk to health. Irritant Substances which can cause inflammation of the skin. Oxidising Substances which may cause other things to burn. 3

NES/Chemistry 1. Safety in the Laboratory Chemistry lessons take place in Chemistry Laboratories. It is quite different from being in a normal classroom. In the laboratory you will see there are the following: Electrical Sockets Water taps Gas Taps Fume cupboards Bottles of chemicals You will be planning and carrying out experiments most lessons in chemistry. This must be done both safely and accurately. The following list of safety rules must be followed at all times:  Do not enter a laboratory without a teacher  Do not eat, or drink in a laboratory  Do not run in a laboratory  Stand when doing experiments, with stools and bags under the bench  Tie long hair back for experiments  Tell the teacher if you spill a chemical, or break apparatus  If you spill chemical on your hands, wash them straight away, then tell the teacher  Follow your teacher's instructions at all times Safety goggles are available, your teacher will tell you when you need to use them. Please clean up after yourself and put apparatus away neatly. Waste Disposal Solid waste Should be put in the bin. Liquid waste Should be put in the sink. Mixed Solid and Liquid Waste Must be put in a special waste container. Broken Glass There is a yellow ‘sharps bin’ for broken glass and sharp pieces of metal. You must tell your teacher if you break glass If you do not know what to do – ask your teacher, they will help you. 4

NES/Chemistry Hazards The substances used in a chemistry laboratory are safe, if used properly. However, some chemicals can cause specific problems, so they are labelled with Hazard Symbols. Symbol Hazard Explosive: Substances which may explode if heated, exposed to a flame, or knocked. Toxic: Substances which may cause death by poisoning. Flammable: Substances which may catch fire easily. Corrosive: Substances which can burn and destroy living tissue. Harmful: Substances which represent a moderate risk to health. Irritant: Substances which can cause inflammation of the skin. Oxidising: Substances which may cause other things to burn. 5

NES/Chemistry 2. Using Apparatus Apparatus are pieces of equipment that are used in a laboratory for a specific purpose. Each piece of apparatus has its own particular use and should be chosen carefully when planning experiments. How to Draw Apparatus Apparatus are always drawn with a pencil, using a ruler when required, as flat 2-dimensional pictures and always with labels. When more than one piece of apparatus is being used in an experiment, then they are usually drawn put together to show how they are being used. In questions which require you to draw apparatus, make sure you label each piece separately. The first test tube is correct because it is 2-dimension and the top is shown as an opening. The second test tube is drawn incorrectly because it is 3-dimension and the top of the test tube is not shown open. Test tube Beaker Apparatus Diagrams Filter paper Filter funnel Round-bottomed Conical flask Spatula Stirring rod flask 6

Stop clock Electronic mass NES/Chemistry balance Measuring cylinder Thermometer Tripod T Wire gauze Evaporating basin Bunsen burner HEAT Pipe clay triangle Separating funnel Pestle and Mortar Delivery tube Scales Any piece of apparatus with a scale must have a scale drawn on it in your diagrams, such as the thermometer, gas syringe and measuring cylinder 7

NES/Chemistry Uses of Apparatus Collecting & Holding Use Apparatus A small glass tube for reacting solids, or liquids Test tube OR heating small amounts of solid Test tube holder Used to hold test tubes during heating. Test tube rack Used to hold several test tubes in an upright position. Boiling tube A slightly larger test tube. Used when heating small amounts of liquids. Capillary tube A small glass tube which is used to transfer tiny volumes of liquids. Beaker A container for reacting, heating, or holding larger volumes of chemicals. Conical flask Similar to a beaker, but cone shaped to allow swirling to mix liquids together. Round-bottom flask Used for heating liquids. Delivery tube Used to transfer gases. Gas jar Used to hold, or collect gases. Spatula Used to transfer small amounts of solid chemicals. Stirring rod Used to mix chemicals. Measuring Apparatus Use Measuring cylinder Used to measure volumes of gases and liquids. Mass balance Used to measure the mass of solids and liquids. Thermometer Used to measure the temperature of a substance. Timer/Stop clock Used to measure time. Gas syringe Used to collect gases. They usually have a scale, so the volume of gas can be measured. 8

NES/Chemistry Uses of Apparatus Separating Use Substances Apparatus Separating funnel A glass funnel, with a tap, used to separate immiscible liquids. Filter funnel Used to separate insoluble solids from liquids. Filter paper Paper with tiny holes in it which separates insoluble solids from liquids. Fractionating column A glass column which separates liquids with different boiling points. Liebig condenser A glass tube which is cooled by an outer layer of water to condense gases to liquids. Heating Apparatus Use Electric heater Used to heat flammable substances. Bunsen burner Used to heat non-flammable substances. Heat proof mat A mat which is placed under a Bunsen burner to protect the bench. Tripod Used to support other pieces of apparatus. Gauze Used to spread out heat, for more controlled and gentle heating Pipe clay triangle To allow direct heating Crucible A small clay, or metal pot, with a lid, used to heat substances strongly. Tongs Used to move hot pieces of apparatus. Other Apparatus Use Pestle and Mortar Used to crush solids into smaller pieces. Watch glass A small glass dish used to hold and spread out liquids. 9

NES/Chemistry Drawing Apparatus joined Together Connecting apparatus together can be quite difficult. The pieces have to fit together properly and be drawn with a pencil and ruler. Rubber bungs should be drawn in ‘cross- section’ showing how the delivery tube, funnel, or thermometer fits. Example: Bung Delivery tube Conical flask Water 10

NES/Chemistry Bunsen Burner The Bunsen burner is the usual way of heating non-flammable substances in a laboratory. It is safe to use if you always remember the following: 1. Before lighting a Bunsen burner, you must check the air hole is closed and there is nothing above the Bunsen burner (like a tripod, or beaker). 2. Have the lit splint ready at the top of the chimney before turning on the gas tap. 3. Make sure the Bunsen burner is on a heat proof mat. 4. The type of flame is controlled by turning the collar. 5. The Bunsen burner is switched off by turning the gas tap off. 6. Do not touch the Bunsen burner until it has cooled down. Parts of a Bunsen Burner Part Purpose Gas tube Connects the Bunsen burner to the gas tap. Base The stand that supports the Bunsen burner Collar Used to open and close the air hole Air hole Lets air into the Bunsen burner Gas jet Forces the gas up the chimney at high speed Chimney Where the gas and air mix 11

Colour of Flame Types of Bunsen Burner Flame NES/Chemistry Yellow Air-hole Use Blue/Yellow Closed Safety flame Blue Half-open Gentle heating Strong heating Open Properties of the Bunsen Burner Flames When the air hole is open, air goes into the Bunsen burner and mixes with the gas. This allows the gas to burn better by providing more oxygen. This is called complete combustion and a blue flame is produced. When the air hole is closed, the gas does not mix with air before it is burned and this leads to incomplete combustion. This is because there is not enough oxygen. The gas burns at a lower temperature producing a yellow flame due to glowing particles of unburnt carbon. These particles make the black smoke (called soot) that can be seen above the flame. They slowly fall back to the ground. You may have seen these unburnt particles of carbon as ash after a fire. Yellow Flame Blue Flame Smokey Not Smokey Quiet Roaring Luminous Flickers and moves Non-luminous Still 12

NES/Chemistry Vacuum Thermometer Glass stem Liquid There are different types of thermometer for measuring Bulb temperature. In chemistry you will be using a liquid-in-glass thermometer. To measure the temperature of a liquid correctly, totally immerse the bulb of the thermometer under the surface of the liquid. As the temperature increases, the liquid expands and moves up the glass stem and the temperature is measured on the scale. The liquid inside the thermometer is either alcohol (which is a red colour), or mercury (which is a silver colour). Mercury Alcohol Measures up to 300 OC Measures up to 100 OC More accurate Less accurate Toxic Harmful Pestle and Mortar A pestle and mortar is used to crush solids into smaller pieces. This increases the amount of solid that is exposed and makes dissolving and reacting faster. Pipe Clay Triangle & Gauze These two pieces of apparatus have different functions and are never used together.  Gauze is used to spread out heat from a Bunsen burner. This will make the heating less intense.  A pipe clay triangle allows the Bunsen burner flame to directly touch the apparatus being heated, usually a crucible. This results in a stronger heating. 13

NES/Chemistry 3. Taking Measurements Any piece of apparatus that is used for measuring, like a measuring cylinder, must be drawn in diagrams with a scale shown. Physical property Measure with Units Time Stop clock Hours / hr Minutes / min Temperature Thermometer Seconds / s Mass Degrees Celsius / OC Volumes Mass balance Kilograms / kg Measuring cylinder Grams / g Gas syringe Litre / dm3 Cubic centimetres / cm3 Time Stop clocks are used to measure time. The units for time are hours, minutes and seconds  1 minute = 60 seconds = 3600 seconds  1 hour = 60 minutes Temperature Thermometers are used to measure temperature using the Celsius scale, which is based on the freezing point of water, 0 OC, and boiling point of water, 100 OC. Mass Mass balances are used to measure mass; they are usually electronic and accurate to 2 decimal places. The units for mass are kilograms and grams.  1 kilogram = 1000 grams 14

NES/Chemistry Volume Measuring cylinders are the simplest way to measure volume. They come in a variety of sizes and we use the smallest measuring cylinder possible to be accurate. Pipettes and burettes are even more accurate. When reading a measuring cylinder, pipette, or burette you will see a meniscus. This is an upward curve (usually) at the edges of the measuring device. To use a measuring cylinder accurately:  Place the measuring cylinder on a flat surface  Make sure your eye is level with the meniscus to avoid making a parallax error  Read the scale from the bottom of the meniscus The units for volume are litres and cubic centimetres.  1 litre = 1000 cubic centimetres Note – sometime another unit, millilitres, are used. These have the same value as cubic centimetres.  1 millilitre = 1 cubic centimetre  1 ml = 1 cm3 Parallax Error This is when a scale is read incorrectly due to not looking at the scale at the correct level. The reading will appear to be a different value if seen from above, or below the correct level. 15

NES/Chemistry Topic 2 – Scientific Method This topic is split up into the following parts: 1. The Scientific Method 2. Variables 3. Planning your own Experiment Independent Variable Definitions Dependent Variable Controlled Variables The variable that is being changed during an experiment We decide what variable we are investigating, e.g. do something every 30 seconds - time is the independent variable The variable that is being measured during an experiment This is what we measure, e.g. measure the temperature with a thermometer every 30 seconds. Temperature is the dependent variable. Variables that are being kept the same during an experiment 16

NES/Chemistry 1. The Scientific Method The scientific method is a way to ask and answer scientific questions by making observations and doing experiments. The steps to doing this are  State a problem/question  Do background research  Construct a hypothesis  Test your hypothesis by experiments  Analyse your data/results and state a conclusion 1. Ask a Question The scientific method starts when you ask a question about something that you observe. For the scientific method to answer the question, it must be about something that you can measure. 2. Research Before you try to construct a hypothesis, it would be sensible to research the topic using the library and the internet. This way you will not repeat mistakes from the past and find the best way of planning your experiment. 3. Hypothesis The word hypothesis means ‘a possible explanation for observations, based on knowledge and research.’ Your hypothesis should be a simple statement that defines what you think the result of your experiment will be. You must state your hypothesis in a way that you can easily measure and answers your original question. 4. Experiment This is where you test your hypothesis by doing an experiment. You must make sure that this is a fair test, changing only 1 variable at a time and keeping all other variables constant. It might also be a good idea to repeat your experiment to make sure your results are accurate and reliable. 5. Conclusion This is the final step of the scientific method and a summary of your results. You can use your results to prove that your hypothesis is correct. If not, then you can reject your hypothesis and possibly use this information to come up with a new question and start the scientific method over again. 17

NES/Chemistry 2. Variables It is important for an experiment to be a fair test. To do this you only change one factor at a time while keeping all other conditions the same. Scientists call the changing factors in an experiment ‘variables’. There are three types of variables: independent, dependent and controlled. Independent Variable This is what is being changed by you in your experiment. There should only be one independent variable in an experiment to ensure a fair test. Dependent variable This is what is being measured during the experiment. It should be the factor that is changing in response to us changing the independent variable Controlled Variables These are factors which have to be kept constant to make sure that they do not have any effect on the experiment, making certain that a fair test is being carried out. If we did change more than one variable at a time, we could not be certain which one was causing the effect to happen. Example of variables in an experiment: Question Does heating a cup of water allow more sugar to dissolve in (What I am investigating) it? Independent variable Temperature of the water (What I change) Dependent variable The mass of sugar that dissolves, in grams (What I observe/measure) Controlled variables Stirring of the sugar (What I keep the same) Type of sugar Volume of water used, in cm3 18

NES/Chemistry 3. Planning your own Experiment Once you have decided what is being investigated, completed your research and written your hypothesis it is time to plan out your experiment. This should include an apparatus list, a diagram of how to set up the apparatus, a method of how to do the experiment and your results. Apparatus You must make a list of what apparatus and chemicals you intend to use during your experiment. This has to be given to your teacher in time for the equipment to be ordered. Some chemicals and apparatus take quite a lot of preparation, so if you do not include it in your list you might end up not being able to do the experiment properly. Think ahead! Diagram A 2-dimensional drawing of how to set up the apparatus in your experiment. All apparatus should be labelled and drawn in pencil, with a ruler. Use the examples on pages 6 and 7 as a guide to help you. Method This lists the steps, or instructions, to be carried out in the experiment. They should be listed in sequence. The words I, He, She, We, etc must not be used in the method. For example ‘I measured 50 cm3 of water’ should be written as ‘Measure 50 cm3 of water using a measuring cylinder’. Someone with no other information should be able to carry out the practical using your instructions, so break them down into simple steps. Results This is where you write what was observed, or measured in your experiment. Data is usually best recorded in a table. Data can also be used to draw a graph of your results. Graphs usually let us see data, trends and patterns more clearly than just tables. We can also use graphs to predict values that lie outside the range of recorded values. Graphs also make it easier to see anomalous values (errors) as they will not be on the line of best fit. 19

NES/Chemistry Evaluation After completing your experiment it is time to evaluate what you did. Think about the following points:  Did you ask the right question at the start?  Could you have written your hypothesis better?  Did you select the correct apparatus and use it properly?  Did you miss out an important step in the method?  Did you accurately record your data?  Was your table of data well presented and helpful?  Did you complete the experiment in the time allowed?  Were your results reliable?  Were your results accurate?  What could you do to improve the experiment? 20

NES/Chemistry Topic 3 – States of Matter This topic is split up into the following parts: 1. Solids, Liquids and Gases 2. Colloids 3. Physical Properties of Materials Viscosity Definitions Fluid Porous A fluids resistance to flow A liquid, or a gas Electrical Conductor Something that has many small holes, so liquid or gas can pass Electrical Insulator through (usually slowly) A substances that electricity can flow through A substance that electricity cannot flow through 21

NES/Chemistry 1. Solids, Liquids and Gases (and Aqueous) Matter is a word used to describe all the different types of substances and materials found in the universe. Matter can exist in one of 3 states: solid, liquid, or gas. For example water can exist as ice (solid), water (liquid) and steam (gas) and each state has different properties even though they are made from the same substance. A common mixture in chemistry is a solution, which is when a solid is dissolved in a liquid (see also Topic 5). We often use the work aqueous to mean a solution of something. Example - aqueous sodium chloride means a solution of sodium chloride in water. Inside Solids, Liquids and Gases All matter is made up of tiny particles which are in constant motion – even solids. The tiny particles are round in shape. Scientists believe that there are forces of attraction holding these tiny particles together, a bit like magnets attracting each other. The more the particles can move, the greater chance they have of overcoming, or breaking, the forces of attraction holding them together. The different states of matter can be explained by the particles in the matter, how they are arranged, how they move and the forces of attraction between the particles. The particles of matter themselves always remain unchanged during physical changes. Arrangement, Movement and Forces of Attraction in Matter Solid Liquid Gas Close together Close together Far apart Arrangement Random Random arrangement arrangement Regular Arrangement Movement Vibrate about a fixed Slip and slide past Rapid, random, position each other continuous motion Forces of Forces of attraction Forces of attraction There are no forces Attraction are strong. are weak of attraction between the atoms 22

NES/Chemistry Properties of Solids, Liquids and Gases Property Solids Liquids Gases Shape Fixed (cannot It can change shape It can change shape Volume change) to fill the bottom of to fill the whole of a Can it be Fixed (cannot a container e.g. container e.g. Compressed? change) beaker balloon Can it Flow? It cannot be Fixed (cannot Can change as a gas compressed change) fills any container No you put it into It cannot be It can be compressed compressed so that it occupies a smaller volume Yes Yes The particles in a solid are held closely together by strong forces of attraction. The particles cannot move over each other, but can vibrate back and forth. There are forces of attraction between particles, but because the particles have more energy they can overcome these forces. They can now slip and slide past each other. There particles now have so much energy that they can break the forces of attraction and move apart. Effectively there are now no forces of attraction between the particles. The particles can now move randomly and rapidly in any direction. 23

NES/Chemistry 2. Colloids This is a mixture in which the particles are larger than in a solution, but smaller than in a suspension. The particles are dispersed (spread out) evenly in the mixture. The different types of colloids are:  Aerosol – solid, or liquid dispersed within a gas. Examples – smoke, clouds, or hair spray  Foam – there are two types of foam:  gas dispersed within a liquid. Example – foam, or froth  gas dispersed within a solid. Examples – pumice stone, or meringue  Emulsion – liquid dispersed within a liquid. Examples – milk, or mayonnaise  Gel – solid dispersed within a liquid, which has set to form a jelly. Example – hand sanitizer, hair gel, or jam 24

NES/Chemistry 3. Physicals Properties of Materials Particle Size Solids vary in particle size from very large, to very small. Usually solids are called coarse (large), fine (small), or powders (very small). Flow Gases and Liquids can flow – move from one place to another in a steady stream. This is because there are only weak forces of attraction between the particles. Sometimes solids can also flow. This usually happens when a solid is a powder with very small sized particles, so the particles can slip and slide over each other like a liquid. Viscosity How sticky or thick a substance is. A substance with a low viscosity is said to be ‘thin’ and flows easily, water, for example. A substance with a high viscosity is said to be ‘thick’ and flows slowly, honey, for example. Porous When a solid substance has lots of tiny holes in it, allowing a liquid, or gas, to flow through it. Electrical Conductivity Some substances allow an electric current to flow through them – these substances are called electrical conductors. Examples – metals, or graphite. Other substances do not allow an electric current to flow through them – these are called electrical insulators. Examples – plastic, or wood. Density A measure of how much mass, of a substance, there is in a fixed volume. The density of a substance is found by dividing its mass by its volume. The units of density are g/cm3. Water has a density of 1 g/cm3, so 100 cm3 of water would have a mass of 100 g. Objects that float in water have a density of less than 1 g/cm3 and substances that sink in water have a density of more than 1 g/cm3. 25

NES/Chemistry Topic 4 – Physical Changes This topic is split up into the following parts: 1. Change of State 2. Heating and Cooling Curves 3. Diffusion Melting Definitions Boiling Freezing The change of state from solid to liquid Condensing The change of state from liquid to gas Sublimation The change of state from liquid to solid Endothermic The change of state from gas to liquid Exothermic The change of state from solid to gas, or gas to solid Diffusion A change that takes in heat energy A change that gives out heat energy The gradual movement of particles from an area of high concentration, to an area of low concentration, until evenly mixed. 26

NES/Chemistry 1. Change of State A change of state occurs when a solid becomes a liquid, or a liquid becomes a gas, etc. Changes of state are physical changes and they are easy to reverse. We do not make a new substance during physical changes, for example ice, water and steam are all made of the same substance. However, the arrangement and movement of the particles in the three states is different. When ice melts it becomes a liquid, called water, and if we heat the water further it evaporates to form a gas, called steam. We can reverse this change, so that if we cool steam then it condenses to make liquid water, and if we cool the water down further then it freezes to make a solid. It is important to realize that not only water can do this - all of the substances in the universe can change state. 1a. Changing State by Changing Temperature  To change a solid into a liquid, or a liquid into a gas the atoms have to gain energy. Melting and evaporation are endothermic changes and they need energy to be put in.  To change a gas into a liquid, or a liquid into a solid then the atoms have to lose energy. Condensation and freezing are exothermic changes and give out energy. GAS Evaporating Condensing or Boiling More energy LIQUID Less energy Melting Freezing SOLID 27

NES/Chemistry Melting When we heat a solid the atoms gain energy from the heat. The atoms vibrate more and the space between the particles increases because the particles have more energy and are able to overcome the forces of attraction. This makes the solid expand, the particles take up more space and so the solid becomes larger. The particles do not change size; they simply take up more space because they vibrate more at a higher temperature. If we continue to heat the expanded solid, then the particles continue to vibrate more and as the particles gain even more energy. They overcome the forces of attraction between the particles and the solid can no longer hold itself together. It collapses to form a liquid, in which the particles ‘slip and slide’ around each other. Diagram Here we see a solid being heated (left). The solid expands (middle) and then it melts (right). Notice that the particles do not change size. 28

NES/Chemistry Evaporation If we heat a liquid then the particles gain energy and move faster and faster. The particles eventually gain so much energy that the forces of attraction between the particles break completely and the particles are free to move as a gas. They spread out as far as they can and they move rapidly, randomly and continuously. Diagram Here we see a sample of liquid being heated (left). The particles move faster and the forces of attraction between the particles break until the particles are free to move rapidly, randomly and continuously as a gas (right). The particles begin to move as far apart from each other as possible. Evaporation and Boiling Liquids can evaporate at any temperature, whereas boiling only happens at the boiling point. For example – water can evaporate in a room at 25 OC, but only boils at 100 OC. Evaporation happens only at the surface of the liquid, but boiling happens throughout the liquid, and you can see all of the liquid bubbling. 29

More energy NES/ChemistryLess energy Condensation This is essentially the opposite of evaporation, so we start with a sample of gas and cool it down until it becomes a liquid. The particles of gas lose energy and move more slowly. As the particles get closer, forces of attraction begin to form between the particles and then the particles start to slip and slide over each other in the liquid state. Freezing This is essentially the opposite of melting, so we start with a sample of liquid and cool it down until it becomes a solid. The particles of liquid lose even more energy; move more slowly, and then they line up in rows with strong forces of attraction between the particles. Sublimation This occurs when a solid changes directly from a solid to a gas, or a gas directly to a solid, missing out the liquid state. Examples of substances that sublime are: iodine, carbon dioxide, graphite and ammonium chloride. GAS Sublimation SOLID 30

NES/Chemistry Melting Point and Boiling Point Melting Point – This is the temperature at which a solid becomes a liquid. Boiling Point – This is the temperature at which a liquid becomes a gas. Freezing Point - This is the temperature at which a liquid becomes a solid. Condensing Point - This is the temperature at which a gas becomes a liquid. At 0 OC ice melts and turns from a solid to a liquid (water). At 100 OC water boils and turns from a liquid to a gas (steam). It is important to remember that different substances have different melting and boiling points. Not all substances melt at 0 OC and boil at 100 OC, only water. Other substances have different melting and boiling points: Substance Melting point / OC Boiling point / OC Oxygen -218 -183 Salt (sodium chloride) 801 1413 661 2467 Aluminium 1538 2862 Iron -182 -164 -117 Methane 3550 78 Ethanol 4826 Diamond 1b. Changing State by Changing Pressure Gases can be compressed and expanded because there are large spaces between their particles. If a gas is compressed enough under high pressure, it can turn into a liquid and then a solid. Once the pressure is removed the solid liquid will change back to a liquid and then a gas again. This is just like melting and boiling, except the change happens because of changing pressure, rather than changing temperature. 31

NES/Chemistry 2. Heating and Cooling Curves If we plot a graph of a substance being heated from a solid until it turns into a gas, it would look like this: Heating Curve As the substance is heated, its temperature increases steadily until the substance changes state. At this point the temperature stops increasing as the energy is being used to break the forces of attraction between the particles instead. Once the substance has completely changed state, the temperature then starts to increase again. It is easy to spot melting and boiling on these graphs – it is always the part of the graph that is horizontal. 32

NES/Chemistry Cooling Curve As you can see, this graph is the opposite of a heating graph, with the horizontal regions being condensing and freezing. A cooling curve usually finishes at 25 OC, which is room temperature. 33

NES/Chemistry Diffusion Diffusion is the gradual movement of particles from a region of high concentration to a region of low concentration until they are evenly mixed, due to the random motion of the particles. The particles do not ever stop moving, but the process of diffusion is complete, as the particles have become evenly mixed, or spread out. Diffusion in Gases Gas particles are far apart and have a lot of energy, so the particles can move quickly. This means that gases diffuse the fastest. The particles move in random directions and often collide into other particles, so it usually takes up to an hour for a gas to diffuse across a room. The following diagram shows what happens when a glass plate is removed from between a gas jar of air and a gas jar of bromine, which is brown in colour. After 1 hour the gas would be evenly mixed. 34

NES/Chemistry Diffusion in Liquids Liquid particles have less energy and the particles are held together more strongly than a gas. Their particles move slower than gases, so liquids diffuse slower than gases. It can take up to a week for a liquid to diffuse in a container like a beaker. Beaker Particles of water Particles of sugar In stage 1 the solid sugar is dissolving in the water In stage 2 the dissolved sugar is diffusing throughout the entire beaker Diffusion in Solids Particles in a solid have the least energy and are the closest together; they diffuse the slowest of all the states of matter. In fact, because the particles diffuse so slowly we say that solids do not diffuse. It would take many, many years for a solid to diffuse. 35

NES/Chemistry Topic 5 – Mixtures This topic is split up into the following parts: 1. Purity 2. Solutions 3. Air Definitions Solution A clear mixture of a solute and a solvent Solute A solid that dissolves in a solvent to form a solution Solvent A liquid in which a solute can dissolve to form a solution Suspension A cloudy mixture of an insoluble solid and a liquid Soluble A substance that can dissolve in a solvent Insoluble A substance that cannot dissolve in a solvent Solubility How much solid (in grams) that can dissolve in 100cm3 water 36

NES/Chemistry 1. Purity Pure substances A pure substance contains only one chemical. It has its own physical properties as well as fixed melting and boiling points. For example, pure water melts at 0 OC and boils at 100 OC. Impure Substances, or Mixtures When a pure substance is mixed with another chemical , without reacting, it becomes an impure substance, or a mixture. The substances in a mixture can always be separated again quite easily (see Topic 6 later). A mixture is not in a fixed ratio. This means that you can change the amount of one of the substances in the mixture. For example you could have a mixture of sand and sugar in a beaker. The ratio of sand and salt is not fixed, so you could add more sand to the beaker and it would still be a mixture. The impurity that is added has an effect on the physical properties of the original substance. The melting point is lowered and the boiling point is raised. For example, when you add an impurity like salt to pure water then the impure water will have a melting point less than 0 OC and a boiling point of more than 100 OC. Impure substances melt and boil over a range of temperatures, rather than at one fixed value. Substance Melting point / OC Boiling point / OC Pure water 0 100 Impure water -10 to -5 105 to 110 37

NES/Chemistry 2. Solutions A solution is a clear mixture of a liquid, usually water, and a soluble solid. The solid breaks down into smaller and smaller pieces until they cannot be seen any more. For example, if you dissolve sugar in water you can no longer see the sugar particles because they are too small, but if you drink the solution you can still taste the sugar because the sugar particles are still there. Dissolving This is a physical change. It happens when a solute dissolves and is absorbed (mixed) in a solvent to form a solution. There are three ways of speeding up dissolving:  Heat the solvent  Stir the solvent  Crush the solute into smaller pieces Both heating and stirring makes the solute dissolve faster by making the solvent particles move faster. This results in the solute and solvent particles hitting each other more often helping the solute particles break apart from each other. When a solute dissolves only the exposed particles at the surface can collide with the solvent particles, so the particles inside have to wait until the particles on the outside dissolve before they can. If you crush a solid, then you are exposing more particles at the surface, so they can dissolve faster. Solubility Solubility is a measure of how much solute will dissolve in a solvent. It is determined by finding out the mass of a solute that will dissolve in 100 g of solvent. When you can dissolve no more solute in a solvent the solution is said to be saturated. If a solvent can dissolve more solute then it is said to be unsaturated. 38

NES/Chemistry Changing Solubility Usually the hotter a solvent is the more solute it can dissolve. The graph shows how the solubility of six different solutes changes with temperature:  In general all the solutes increase in solubility as the temperature increases.  The most soluble substance, at any temperature, is potassium iodide because the line for this solute is the highest on the graph.  The solubility of sodium chloride does not change much with temperature because the graph is flat. 39

NES/Chemistry Suspension A cloudy mixture of an insoluble substance mixed with a liquid. With time, the particles will sink to the bottom of the container. The particles of the substance do not break down and can still be seen Examples – chalk and water, or sand and water. 40

NES/Chemistry 3. Air Air is a layer of gases around the Earth. It is about 700 km thick. As you rise above the Earth the atmosphere thins out (gets less concentrated). Composition of Air Clean air is made up of a mixture of the following gases: Gas Abundance Nitrogen 79% Oxygen 20% Argon Almost 1% Carbon dioxide 0.03% Helium Trace amounts Water vapour Variable, up to 4% Nitrogen Nitrogen is the main component of air. It is colourless and odourless and not very reactive. Uses of nitrogen:  Liquid nitrogen is very cold and used to quick-freeze food.  Nitrogen is used in food packaging as it is unreactive and stops food going off as it replaces the oxygen that microbes require to respire. Oxygen Oxygen is the reactive gas in air. It is the gas in air that living organisms need to survive. It is the gas that causes food and living materials to decompose, as well as essential for combustion. In fact oxygen is the most important gas in air. Uses of oxygen:  Oxygen is carried by astronauts and deep sea divers for breathing.  Steel making  Welding and cutting metals 41

NES/Chemistry Other Gases in Air Argon  inert atmosphere for welding metals Carbon dioxide  in fire extinguishers  making fizzy drinks Helium  lighter-than-air balloons  coolant for MRI scanners 42

NES/Chemistry Topic 6 - Separating Techniques This topic is split up into the following parts: 1. Filtration and Decanting 2. Evaporation 3. Distillation 4. Separating Funnel 5. Chromatography Definitions Filtrate The liquid, or solution that passes through the filter paper Distillate The liquid product that is condensed from gas during distillation Residue The substance left behind during filtration, evaporation, or distillation 43

NES/Chemistry Methods of Separation There are several different physical methods of separating mixtures based on which substances are in the mixture. Mixture Method of separation Decanting Suspensions (insoluble solid and liquid) Filtration Solutions (soluble solid and liquid) Evaporation Simple distillation Miscible liquids Fractional distillation Immiscible liquids Separating funnel Several solutes in one solvent Chromatography 44

NES/Chemistry 1a. Decanting Decanting is a method of separating a suspension into a solid and a liquid. It is a quick way of separating a suspension that does not require any apparatus. It works best with larger particles of insoluble solid. Once the suspension has settled and all the solid particles are at the bottom of the container, the liquid can be poured off the solid leaving the solid particles behind. 1b. Filtration Filtration is also a method of separating a suspension into a solid and a liquid. It gives a better separation compared to decanting, but takes longer and requires filter paper. The filter paper is porous having lots of tiny holes in the paper which allows the liquid to pass through. The insoluble solid particles are too large to pass through the tiny holes so they stay on the filter paper. During filtration the solid left in the filter paper is called the residue and the liquid that passes through the filter paper is called the filtrate. Filtration does not work on solutions because the solute particles are small enough to pass through the filter paper. 45

NES/Chemistry 2. Evaporation Evaporation is a method of separating a solution into a solid and a liquid. The solution is placed in an evaporating basin and heated causing the solvent to boil. The solute remains behind in the evaporating basin as it has a much higher melting and boiling point. This method only works if you want to collect the solute as the solvent is lost to the air when it boils away. A heating bath is often used, as the heating is more gentle. This stops 'spitting' where the solute can jump out of the evaporating basin when there is very little water left. 46

NES/Chemistry 3a. Simple Distillation Simple distillation also separates solutions. It works in a similar way to evaporation, but the solvent gas is collected as well. The solute remains in the round bottom flask (the residue) and the solvent passes through the water cooled condenser and is collected in the conical flask (the distillate). The solution is heated and the solvent will start to boil. The solute will remain in the round bottom flask as it has a much higher melting and boiling point. Anti-bumping granules are added to make the distillation smoother to avoid gas loss, or breakages as well as stopping the liquid from shooting up into the Liebig condenser. As the solvent gas rises up and passes through the Liebig condenser we can check the temperature with a thermometer. It will be the same temperature as the boiling point of the liquid being collected. The Liebig condenser is cooled by water and this cools the solvent gas enough to condense it back to a liquid. This can be collected at the end of the Liebig condenser as the distillate. Note – for any distillation, or evaporation involving a flammable liquid, like ethanol or oil, you must not use a Bunsen burner for heating. An electric heater must be used instead. 47

NES/Chemistry 3b. Fractional Distillation Fractional distillation is a method of separating miscible liquids. It is similar to simple distillation, but has a fractionating column where the separation occurs. This method works because the liquids have different boiling points. When the miscible liquids are heated in the round bottom flask they will all evaporate. The gases rise up the fractionating column where they start to cool down. The gas with the highest boiling point will condense first and fall back down the column. The other gas (with the lowest boiling point) will continue to rise up the column and pass into the Liebig condenser. The condenser will cool the gas and condense it back to liquid. It is collected as the distillate in the conical flask. The thermometer is used to check which liquid is being collected in the conical flask. For example if a mixture of ethanol and water were being distilled:  The temperature on the thermometer will rise from room temperature as the mixture is heated.  The first distillate is collected and the thermometer will remain at 78 0C until all the ethanol has boiled.  The temperature will rise again until the second liquids boils.  The second distillate is collected and the thermometer will read 100 0C until all the water boils. 48

NES/Chemistry 4. Separating Funnel A separating funnel is used to separate a mixture of immiscible liquids. The mixture must be left to allow the two different liquids to separate into layers. The more dense liquid will be at the bottom and the less dense liquid at the top. The separating funnel has tap at the bottom which can be use to pour out the more dense liquid from the bottom. The following diagram show the separation of oil (less dense) and water (more dense): 49