Y10 Chemistry Revision Guide (PDF)

# Y10 Chemistry ## Unit 1 ### Principles of Chemistry #### Part 1 #### Revision Material *The diagram shows the three states of matter (Solid, Liquid and Gas) and transitions between them.* * Solid - Ice * Liquid - Water * Gas - Water Vapour * Transitions: Melting, Freezing, Warming, Cooling, Evap...

# Y10 Chemistry ## Unit 1 ### Principles of Chemistry #### Part 1 #### Revision Material *The diagram shows the three states of matter (Solid, Liquid and Gas) and transitions between them.* * Solid - Ice * Liquid - Water * Gas - Water Vapour * Transitions: Melting, Freezing, Warming, Cooling, Evaporating, Condensing* ## SECTION 1 - PRINCIPLES OF CHEMISTRY ### States of Matter You can explain quite a bit of Chemistry if you can get your head round this lot. ### The Three States of Matter - Solid, Liquid and Gas Materials come in three different forms - solid, liquid and gas. These are the Three States of Matter. Which state you get (solid, liquid or gas) depends on how strong the forces of attraction are between the particles of the material. How strong the forces are depends on THREE THINGS: * a) the material * b) the temperature * c) the pressure. ### Solids 1) In solids, there are strong forces of attraction between particles, which holds them close together in fixed positions to form a very regular lattice arrangement. 2) The particles don't move from their positions, so all solids keep a definite shape and volume, and don't flow like liquids. 3) The particles vibrate about their positions - the hotter the solid becomes, the more they vibrate (causing solids to expand slightly when heated). ### Liquids 1) In liquids, there is a weak force of attraction between the particles. They're randomly arranged and free to move past each other, but they tend to stick closely together. 2) Liquids have a definite volume but don't keep a definite shape, and will flow to fill the bottom of a container. 3) The particles are constantly moving with random motion. The hotter the liquid gets, the faster they move. This causes liquids to expand slightly when heated. ### Gases 1) In gases, the force of attraction between the particles is very weak - they're free to move and are far apart. The particles in gases travel in straight lines. 2) Gases don't keep a definite shape or volume and will always fill any container. 3) The particles move constantly with random motion. The hotter the gas gets, the faster they move. Gases either expand when heated, or their pressure increases. ### States of Matter Materials don't just stay in one state. They can change between all three. Clever eh. It all depends on how much energy they have. Read on... ### Substances Can Change from One State to Another Physical changes don't change the particles - just their arrangement or their energy. 1) When a solid is heated, its particles gain more energy. 2) This makes the particles vibrate more, which weakens the forces that hold the solid together. This makes the solid expand. 3) At a certain temperature, the particles have enough energy to break free from their positions. This is called MELTING and the solid turns into a liquid. 4) When a liquid is heated, the particles get even more energy. 5) This energy makes the particles move faster, which weakens and breaks the bonds holding the liquid together. 6) At a certain temperature, the particles have enough energy to break their bonds. This is called EVAPORATING and the liquid turns into a gas. * A red arrow means heat is supplied *A blue arrow means heat is given out ### Changing the energy of particles can cause a change of state Make sure you can describe what happens to the energy of the particles, and the forces between them, as a substance is heated and cooled. Remember the terms for each state change too. ## SECTION 1 - Particles and Mixtures ## Movement of Particles There are many nifty experiments that you can do to observe the wonders of chemistry. Here are a few... ### Diffusion is the Movement of Particles Through a Liquid or Gas Diffusion is the gradual movement of particles from places where there are lots of them to places where there are fewer of them. It's just the natural tendency for stuff to spread out. You can use the experiment below to demonstrate diffusion... ### Potassium Manganate(VII) and Water Potassium manganate(VII) is great for this experiment because it's bright purple: 1) If you take a beaker of water and place some potassium manganate(VII) at the bottom, the purple colour slowly spreads out to fill the beaker. 2) This is chemistry in action (groan)... The particles of potassium manganate (VII) are diffusing out among the particles of water. 3) It's the random motion of particles in a liquid (see page 1) that causes the purple colour to eventually be evenly spread out throughout the water. ### Potassium Manganate(VII) solution can be diluted by adding water If you were to add more water to the final purple solution, the potassium manganate(VII) particles would spread even further apart and the solution would be less purple. This is called dilution. ## Movement of Particles Here are two more experiments that demonstrate diffusion... ### Ammonia and Hydrogen Chloride 1) Aqueous ammonia (NH3) gives off ammonia gas. Hydrochloric acid (HCl) gives off hydrogen chloride gas. 2) If you set up an experiment like this... *diagram* you'll get a white ring of ammonium chloride forming in the glass tube. 3) The NH3 gas diffuses from one end of the tube and the HCl gas diffuses from the other. When they meet they react to form ammonium chloride. 4) The ring doesn't form exactly in the middle of the glass tube- it forms nearest the end of the tube where the hydrochloric acid was. 5) This is because the particles of ammonia are smaller and lighter than the particles of hydrogen chloride, so they diffuse through the air more quickly. ### Bromine Gas and Air 1) Bromine gas is a brown, strongly smelling gas. You can use it to demonstrate diffusion in gases. 2) Fill half a gas jar full of bromine gas, and the other half full of air- separate the gases with a glass plate. *diagram* 3) When you remove the glass plate, you'll see the brown bromine gas slowly diffusing through the air. 4) The random motion of the particles means that the bromine will eventually diffuse right through the air. *diagram* ### Sleeping on the book won't make the words diffuse into your head... If you're lucky, you might get to see these experiments in the lab. Or, your teacher might show you some equally exciting but different experiments to demonstrate diffusion of particles. ## Filtration and Crystallisation Remember, the components of mixtures are not chemically joined (see page 6). This means you can separate them very easily using physical methods. ### Filtration is Used to Separate a Insoluble Solid from a Liquid 1) Filtration can be used if your product is an insoluble solid that needs to be separated from a liquid reaction mixture. 2) It can be used in purification as well. For example, solid impurities in the reaction mixture can be separated out using filtration. *diagram* ### Crystallisation is Used to Separate a Soluble Solid from a Solution Here's how you crystallise a product... 1) Pour the solution into an evaporating dish. 2) Slowly heat the solution. Some of the solvent will evaporate and the solution will get more concentrated. Stop heating when crystals start to form. 3) Remove the dish from the heat and leave it in a warm place for the rest of the solvent to slowly evaporate - this way you get nice big crystals. 4) Finally, you've got to dry the product - you can use a drying oven or a desiccator for this (a desiccator contains chemicals that remove water from the surroundings). *diagram* ## Filtration and Crystallisation Here's how you can put filtration and crystallisation to good use. Separating rock salt... ### You Can Use Filtration and Crystallisation to Separate Rock Salt 1) Rock salt is simply a mixture of salt and sand (they spread it on the roads in winter). 2) Salt and sand are both compounds - but salt dissolves in water and sand doesn't. This vital difference in their physical properties gives a great way to separate them. 3) You need to learn the four steps of the method: 1) **Grinding**- Grind up the rock salt with a pestle and mortar. 2) **Dissolving** - Dissolve in beaker and stir. 3) **Filtering** - Filter through filter paper in a funnel. 4) **Crystallisation** - Evaporate in an evaporating dish. 4) The sand doesn't dissolve (it's insoluble), so it stays as big grains. These won't fit through the tiny holes in the filter paper so it collects on the filter paper. 5) The salt is dissolved in solution, so it does go through - and when the water's evaporated, the salt forms as crystals in the evaporating dish. ### Revise mixtures — just filter out the important bits... Before you dash on to the next page (I know, I know, it's just so exciting), make sure you've learnt all the details on this page first. The next page will still be there when you're done. ## Chromatography Chromatography is another method used by chemists to separate out mixtures. You can use paper chromatography to separate out dyes — e.g. in inks, paints, food colourings etc. It's, er, fascinating stuff. ### You Need to Know How to Do Paper Chromatography: 1) Draw a line near the bottom of a sheet of filter paper. (Use a pencil to do this - pencil marks are insoluble and won't react with the solvent.) *diagram* 2) Add spots of different dyes to the line at regular intervals. *diagram* 3) Loosely roll the sheet up and put it in a beaker of solvent, e.g. water. *diagram* 4) The solvent used depends on what's being tested. Some compounds dissolve well in water, but sometimes other solvents, like ethanol, are needed. 5) Make sure the dyes aren't touching the solvent - you don't want them to dissolve into it. 6) Place a lid on top of the container to stop the solvent evaporating. 7) The solvent seeps up the paper, carrying the dyes with it. 8) Each different dye will move up the paper at a different rate and form a spot in a different place. 9) The end result is a pattern of spots called a chromatogram. *diagram* ### Chromatography separates dyes in inks Always draw the line at the bottom of the filter paper in pencil. If you do it in pen, the dyes in the pen's ink will dissolve in the solvent and mess up your results. Which would be annoying. ## Chromatography Now that you know how to do chromatography, it's time to find out how it works. ### How Chromatography Separates Mixtures 1) Chromatography works because different dyes will move up the paper at different rates. 2) Some will stick to the paper and others will dissolve more readily in the solvent and travel more quickly. 3) The distance the dyes travel up the paper depends on the solvent and the paper you use. ### Chromatography Can Help You to Identify Dyes 1) If you want to work out what dyes are present in an unknown substance (e.g. an ink), you can use chromatography to find out. 2) First make chromatograms for your unknown substance and for some reference materials (dyes that you think might be in the ink). 3) Now compare the chromatograms to work out what dyes are in your unknown substance - spots on the chromatogram for the unknown substance will match spots on the chromatograms of the reference materials when the dyes are the same. #### Example: *diagram* You can see from the position of the spots on the filter paper that the unknown ink contains dye A and dye C. ### Different dyes move up the paper at different rates... So that's chromatography - it's pretty neat once you get your head around it. You can even use it for crime-fighting... CSIs use chromatography to identify unknown substances from crime scenes. They can even use it to identify inks used to print forged money and link 'em back to a suspect. ## Distillation Distillation is used to separate mixtures that contain liquids. There are two types that you need to know about - simple and fractional. ### Simple Distillation is Used to Separate Out Solutions 1) Simple distillation is used for separating out a liquid from a solution. 2) The solution is heated. The part of the solution that has the lowest boiling point evaporates. 3) The vapour is then cooled, condenses (turns back into a liquid) and is collected. 4) The rest of the solution is left behind in the flask. #### Example: You can use simple distillation to get pure water from seawater. The water evaporates and is condensed and collected. Eventually you'll end up with just the salt left in the flask. *diagram* 5) The problem with simple distillation is that you can only use it to separate things with very different boiling points. 6) If you have a mixture of liquids with similar boiling points, you need another method to separate them out - like fractional distillation (see next page). ### Heating ### Evaporating ### Cooling ### Condensing You might have used distilled water in Chemistry lessons. Because it's been distilled, there aren't any impurities in it (like ions, see page 19) that might interfere with experimental results. Clever stuff. Make sure you know the ins and outs of simple distillation before you turn over the page. ## Distillation ### Fractional Distillation is Used to Separate a Mixture of Liquids If you've got a mixture of liquids you can separate it using fractional distillation. Here is a lab demonstration that can be used to model fractional distillation of crude oil at a refinery. *diagram* 1) You put your mixture in a flask and stick a fractionating column on top. Then you heat it. 2) The different liquids will all have different boiling points so they will evaporate at different temperatures. 3) The liquid with the lowest boiling point evaporates first. When the temperature on the thermometer matches the boiling point of this liquid, it will reach the top of the column. 4) Liquids with higher boiling points might also start to evaporate. But the column is cooler towards the top. So they will only get part of the way up before condensing and running back down towards the flask. 5) When the first liquid has been collected, you raise the temperature until the next one reaches the top. ### Fractionating - sounds a bit too much like maths to me... Remember that parts of mixtures aren't joined together so you can separate them by physical methods. You need to learn these techniques so make sure you can scribble all this stuff down. Enjoy. ## Atoms All substances are made up of atoms. There are quite a few different models of the atom - but chemists tend to like this nuclear model best. ### The Nucleus: 1) It's in the middle of the atom. 2) It contains protons and neutrons. 3) It has a positive charge because of the protons. 4) Almost the whole mass of the atom is concentrated in the nucleus. 5) But size-wise it's tiny compared to the rest of the atom. ### The Electrons: 1) They move around the nucleus in energy levels called shells. 2) They're negatively charged. 3) They're tiny, but they cover a lot of space. 4) The size of their orbits determines how big the atom is. 5) They have virtually no mass. * Protons are heavy and positively charged. * Neutrons are heavy and neutral. * Electrons are tiny and negatively charged. ### Number of Electrons Equals Number of Protons 1) Neutral atoms have no charge overall. 2) The charge on the electrons is the same size as the charge on the protons - but opposite. 3) This means the number of electrons always equals the number of protons in a neutral atom. 4) If some electrons are added or removed, the atom becomes charged and is then an ion. ### Atomic Number and Mass Number Describe an Atom These two numbers tell you how many of each kind of particle an atom has. * **The Mass Number**: Total of protons and neutrons * **The Atomic Number**: Number of protons 1) The atomic number tells you how many protons there are. 2) Atoms of the same element all have the same number of protons - so atoms of different elements will have different numbers of protons. 3) To get the number of neutrons, just subtract the atomic number from the mass number. ### Molecules are Groups of Atoms 1) Atoms can join together to form molecules. 2) Some molecules are made from just one element (e.g. H₂, N₂), while others are made up of more than one element (e.g. H₂O, CO₂). 3) Molecules are held together by covalent bonds (there's more on bonds on pages 19-20 and 25-27). ## The Periodic Table In 1869, Dmitri Mendeleev arranged 50 known elements in order of atomic mass to make a Table of Elements. Mendeleev's table placed elements with similar chemical properties in the same vertical groups but he found that he had to leave gaps in his table to make this work. The gaps in Mendeleev's table of elements were really clever because they predicted the properties of undiscovered elements. Since then new elements have been found which fit into the gaps left in Mendeleev's table... ### The Periodic Table is a Table of All Known Elements *diagram* 1) We now know there are 100ish elements that all materials are made of, with more still being 'discovered'. 2) The modern periodic table shows the elements in order of increasing atomic number. 3) The periodic table is laid out so that elements with similar properties form columns. 4) These vertical columns are called groups. 5) The group to which an element belongs corresponds to the number of electrons it has in its outer shell. (Group 1 elements have 1 outer shell electron, Group 2 elements have 2 outer shell electrons and so on.) 6) Some of the groups have special names. Group 1 elements are called alkali metals. Group 7 elements are called halogens, and Group 0 are called the noble gases. ### Elements in a Group Have the Same Number of Outer Electrons 1) The elements in any one group all have the same number of electrons in their outer shell. 2) That's why they have similar properties. And that's why we arrange them in this way. 3) When only a small number of elements were known, the periodic table was made by looking at the properties of the elements and arranging them in groups - the same groups that they are in today. 4) This idea is extremely important to chemistry - so make sure you understand it. The properties of the elements depend on the number of electrons they have. Atomic number is therefore very significant because it is equal to the number of electrons each atom has. But it's the number of electrons in the outer shell which is the really important thing. ## Electron Shells The fact that electrons occupy "shells" around the nucleus is what causes the whole of chemistry. Remember that, and watch how it applies to each bit of it. It's ace. ### Electron Shell Rules: 1) Electrons always occupy shells (sometimes called energy levels). 2) The lowest energy levels are always filled first - these are the ones closest to the nucleus. 3) Only a certain number of electrons are allowed in each shell: * 1st shell - 2 * 2nd shell - 8 * 3rd shell - 8 *diagram* 4) Atoms are much happier when they have full electron shells - like the noble gases in Group 0. 5) In most atoms the outer shell is not full and this makes the atom want to react to fill it. ### Electron shells - probably the most important thing in chemistry It's really important to learn the rules for filling electron shells. It's so important I'll leave this page with a quick recap. The energy of the shells increases with increasing number (so shell 1 is the lowest). Fill the shell with lowest energy first. The 1st shell can only hold a maximum of 2 electrons, but the 2nd and 3rd shells can both hold 8 electrons. Practise following these rules on the next page. ## Isotopes Some elements have more than one isotope. "But what's an isotope?" I hear you cry. Read on... ### Isotopes are the Same Except for an Extra Neutron or Two A favourite exam question is: "Explain the meaning of the term isotope" The trick is that it's impossible to explain what one isotope is. Nice of them that, isn't it! You have to outsmart them and always start your answer "Isotopes are..." LEARN the definition: #### Isotopes are: different atomic forms of the same element, which have the SAME number of PROTONS but a DIFFERENT number of NEUTRONS. 1) The upshot is: isotopes must have the same proton number but different mass numbers. 2) If they had different proton numbers, they'd be different elements altogether. 3) A very popular pair of isotopes are carbon-12 and carbon-14, used for carbon dating. * **Carbon-12** *diagram* * **Carbon-14** *diagram* ### Will this be in your exam — isotope so... Carbon-14 is unstable. It makes up about one ten-millionth of the carbon in living things. When things die, the C-14 is trapped inside the dead material, and it gradually decays into nitrogen. So by measuring the proportion of C-14 found in some old wood you can calculate how long ago it was living wood. ## Relative Atomic Mass Relative atomic mass isn't as bad as it sounds, I promise. Come on, let's take a look... ### Relative Atomic Mass Takes All Stable Isotopes into Account 1) Relative atomic mass (A,) is just a way of saying how heavy different atoms are compared with the mass of an atom of carbon-12. So carbon-12 has an A, of exactly 12. 2) It's the average mass of all the isotopes of an element. It has to allow for the relative mass of each isotope and its relative abundance. 3) Relative abundance just means how much there is of each isotope compared to the total amount of the element in the world. This can be a ratio, a fraction or a percentage. #### Example: Work out the relative atomic mass of chlorine. ||Relative mass of isotope |Relative Abundance| |:--:|:--:|:--:| |Chlorine|35|3| |Chlorine|37|1| *This means that there are 2 isotopes of chlorine. One has a relative mass of 35 (35Cl) and the other 32 (37Cl). The relative abundances show that there are 3 atoms of 35Cl to every 1 of 37CI.* 1) Multiply the mass of each isotope by its relative abundance. 2) Add those together. 3) Divide by the sum of the relative abundances. * (35×3)+(37×1) / (3+1) = 35.5* 4) You can find the relative atomic mass of any element using the periodic table (see the inside of the front cover). 5) Relative atomic masses don't usually come out as whole numbers or easy decimals, but they're often rounded to the nearest 0.5 in periodic tables. ### It's relatively simple once you get your head around it... Fans of statistics will recognise the formula for working out relative atomic mass as a simple weighted average. Just remember which numbers go where and you'll be able to do these in your sleep. ## Warm-Up and Exam Questions Here's a couple of pages of questions to check you've learned all the info. Have a go at the warm-up questions, then get stuck into some proper exam practice. ### Warm-Up Questions 1) Name the two particles that make up the nucleus of an atom. 2) What is the relative mass and charge of each particle in an atom? 3) What is a molecule? ### Exam Questions 1) The photograph shows a vessel in a distillery. The walls of the vessel are solid copper. a) Copy and complete the sentences about solids using words from the box. Each word may be used once, more than once or not at all. * weak, move, colder, hotter, random * strong, expand, heavier dissolve, regular * *In solids, there are _**forces of attraction**_ between particles, which hold them in _**fixed**_ positions in a _**regular**_ arrangement. The particles don't _**move**_ from their positions, so solids keep their shape. The _**hotter**_ the solid becomes, the more the particles in the solid vibrate.* b) Inside the vessel, liquid ethanol is turned into ethanol gas. Describe the changes in arrangement, movement and energy of the particles when the liquid ethanol is heated to become a gas. (4 marks) 2) The diagram shows a substance changing between solid, liquid and gas states. a) Give the letter of the arrow that represents subliming. b) Give the name of the process represented by arrow A. c) Describe what happens to the particles in a solid when it is heated to the point of melting. (4 marks) 3) A student placed a small amount of potassium manganate(VII) in a beaker of water. The potassium manganate(VII) completely dissolved, turning the water nearby purple. Eventually all the water in the beaker was purple. a) Give the name of the process which made the colour spread through the beaker. (1 mark) b) The student then added more water to the beaker. Which sentence correctly explains what happened to the colour of the water? * A The colour was unchanged as the amount of potassium manganate (VII) stayed the same. * B The colour was unchanged as water particles don't react with potassium manganate (VII). * C The water got less purple as some of the potassium manganate(VII) particles reacted. * D The water got less purple as the potassium manganate(VII) particles spread further apart. c) The result of the student's next experiment is shown below. A white ring of ammonium chloride has formed on the glass tube at the point where the hydrogen chloride gas met the ammonia gas. *diagram* Which sentence correctly explains why the ring formed closer to the source of hydrogen chloride than the source of ammonia? * A The air was warmer near the source of the hydrogen chloride, so it evaporated more quickly. * B The particles of ammonia are smaller and lighter, so they diffused more quickly. * C The particles of ammonia were diluted by the air in the tube. * D The particles of hydrogen chloride gas vibrated about a fixed position. 4) The photograph shows the NASA Space Shuttle soon after being launched. The large central tank contains liquid oxygen and liquid hydrogen. In the shuttle's thrusters, oxygen reacts with hydrogen to produce water vapour. *diagram* a) Is liquid oxygen an element, compound or mixture? (1 mark) b) Is water vapour an element, compound or mixture? (1 mark) ## Warm-Up and Exam Questions Here are some useful questions to check you've learnt all the info. ### Warm-Up Questions 1) Which separation technique could you use to separate a soluble solid from a solution? 2) Which technique could you use to separate a mixture of liquids with similar boiling points? ### Exam Questions 1) A forensic scientist is using paper chromatography to compare different inks. a) Describe the method used to set up a paper chromatography experiment to compare the inks. (3 marks) b) The scientist is using paper chromatography to compare an ink used on a document with the ink in three different printers. The chromatogram is shown on the right. Which printers could not have produced the document? *diagram* (1 mark) 2) Lawn sand is a mixture of insoluble sharp sand and soluble ammonium sulfate fertiliser. a) Describe how you would obtain pure, dry samples of the two components in the lab. b) A student separated 51.4 g of lawn sand into sharp sand and ammonium sulfate. After separation, the total mass of the two products was 52.6 g. Suggest one reason for this error. (4 marks) 3) The boiling points of three liquids are shown in the table. a) State why simple distillation cannot be used to separate water from a solution of water and methanoic acid. (1 mark) b) The apparatus shown was used to separate a mixture of propanone and water. Copy and complete the table using the options below. Each option may be used once, more than once, or not at all. * no liquid, water, propanone, both liquids *diagram* c) Explain how fractional distillation works to separate a mixture of liquids. (3 marks) (4 marks)