A Level Chemistry Bridging tasks 2021 Write an essay on your chosen topic. The essay should be no more than two sides of A4 and should include a reference list and diagrams, if appropriate. The essay should be written in an appropriate style and pay due care to spelling, punctuation, grammar and the use of scientific conventions and notation where appropriate.
Essay Titles 1) The development of atomic theory
Describe the development of our understanding of atomic theory. What were the major theories and discoveries that allowed the model to develop?
2) Combating Plastic Pollution. Plastics and polymers have revolutionised the modern world. However, their overuse is now causing a pollution crisis. Describe what polymers are (include diagrams) and the different types. Explain why polymers are causing a pollution problem. Research and describe some possible solutions to the plastic pollution problem.
3) Water and bonding Water has many unusual properties due to the nature of the bonding within it and between its molecules. Describe the nature of bonding in water. Research and describe how and why the physical and chemical properties of water are different to the other hydrides of group 6 (hydrogen sulphide, hydrogen selenide, hydrogen telluride and hydrogen polonide) using data to support your comments. Describe some of the unusual properties of water and the impact that this had had on planet Earth.
Work is due to be submitted in the first week of the new term in September.
The following pages contain reminders of the work you did at GCSE which is still relevant at AS level.
Page 1 - Atomic Structure Page 2 - Calculations Try to complete as many sections as you can. Page 3 - Writing equations Page 4 - Chemical Bonds As a minimum, you should Page 5 - Properties of ionic and covalent compounds read the summaries and attempt 1-2 questions per Page 6 - The Periodic table section. Page 7 - Energy and rates of reactions (kinetics) Page 8 - Reversible reactions (Equilibria) If you are able, you can complete more. Page 9 - Reactivity and metals Page 10-11 - Displacement and Redox reactions The aim is to remind yourself of the core ideas Page 12 - Crude oil and Organic chemistry and principles from GCSE.
Atomic Structure – what is in an atom? Energy levels always Atoms contain fill up from the 7. Two isotopes of chlorine Small dense nucleus comprised of positive bottom are chlorine-35 and protons and neutral neutrons chlorine-37. How many Negative electrons orbit the nucleus in energy protons, neutrons and levels (shells) electrons are there in each An atom is mostly empty space as most of the Questions isotope? mass is concentrated in the nucleus The size of the atom is governed by the numbers of 1. Complete the table 8. How many electrons are orbiting electrons Particle Relative Charge there in Ca2+ ? mass Atoms on the Periodic Table Proton Atomic number, Z – represents the number of Neutron protons in an atom Electron Relative atomic mass, A – represents the number of protons and neutrons added together, 2. How many protons are those particles with mass. there in fluorine?
Properties of atoms 3. How many neutrons are Atoms are electrically neutral as they contain the there in manganese? same number of electrons and protons Atoms gain or lose electrons to become charged – 4. How many electrons are IONS there in bromine? Atoms containing the same numbers of protons but different numbers of neutrons are called 5. What is the charge on ISOTOPES an atom that loses 2 electrons? Arranging electrons Energy level 1 contains 2 electrons – called an s 6. What is the charge on level an atom that gains 3 Energy level 2 contains 8 electrons – split into two electrons? sub-levels, s and p 1 Calculations Add up the masses h. (CH3CO)2O of the elements from i. C6H5OH Mass and moles the periodic table j. Fe2O3 raking into account k. K2Cr2O7 The mole is an amount of chemical. It stands for a fixed the numbers of l. Al2(SO4)3 number of particles. That number is 6.022x1023. The elements m. KMnO4 number is huge! Instead of counting out atoms for Where there are n. CaC2O4 reactions we use a rule to convert masses of substance brackets the small o. CH3COOH into a number of moles and vice versa. number outside the bracket multiplies 1 mole of a substance is the Mr of the substance weighed everything inside the out in grams (g). bracket. 2) Calculate the number of So 1g of H atoms contains 1 mole of H atoms. e.g. Al3(PO4)2 moles of particles in 0.1 kg 1g of H2 molecules contains 0.5 moles of Hydrogen of each substance in molecules as the mass of a molecule of hydrogen is 2. Al = 3 x 27 = 81 questions a-g. (PO4)2 = [31 + (4x16)] x 2 State if the type of particle To convert mass in to moles you need to do mass (g)/Mr = 190 would be atoms or of the substance. molecules or formula mass. Be wary of questions giving mass in kg. You need to Total = 271 convert Kg to g first. (100g in 1kg so times the mass in kg by 1000 first). Questions
Remember n = m . 1) Work out the relative Mr molecular/ formula mass of these elements and Mr can be relative atomic mass for atoms/elements (Ar), compounds. Molecular mass (Mr) for covalent substances or formula a. O2 mass for ionic substances. b. S c. H2O Relative molecular/ formula masses d. CO2 Only tool required is your periodic table e. SO3 f. CaCl2 g. C2H5NH2
2 Writing Equations Lastly you have to 4. Balance your equations In order to write a correct equation you need a balance the equation correct formula. This means you need to learn common Numbers go at the formulae – such as acids - the charges of common ions front and the formulae of polyatomic ions. Once you have Don’t change the these charges the best method is the criss-cross. FORMULAE! Questions E.g. Aluminium nitrate Identify the ions and charges 1. Work out the following 3+ 1- Al and NO3 formulae Put a circle around the number on each charge a. magnesium hydroxide b. lithium bromide 3 + 1- Al and NO3 c. aluminium oxide Criss – cross your numbers d. potassium sulphate e. calcium carbonate 3 + 1 - Al and NO3 2. Complete these word equations Al (NO3)3 a. sodium hydroxide + Al(NO3)3 – you need brackets or it looks like you have hydrochloric acid 33 nitrogens! If the number is a 1 we don’t write it b. aluminium + nitric acid down. = c. magnesium carbonate + With correct formulae you need to recall how sulphuric acid = chemicals react. d. C2H6 + oxygen = - ACID + BASE = SALT + WATER e. Iron + copper sulphate - ACID + METAL = SALT + HYDROGEN = - ACID + METAL CARBONATE = SALT + CARBON DIOXIDE + WATER f. magnesium sulphate + - HYDROCARBON + OXYGEN = CARBON DIOXIDE + WATER barium chloride = - X + YZ = XZ + Y (single replacement) - AB + CD = AD + BD (double replacement) 3. Turn the word Remember certain gases hang out in 2s – H2, N2, O2, equations in qu.2 into halogens symbol equations
3 Chemical Bonds Questions There are three types of chemical bond:- Ionic bonding 1. Explain the formation of Covalent bonding NaCl, MgO and MgCl2. Use Metallic bonding diagrams to illustrate your answers. Ionic Bonding Bond formed between oppositely charged ions 2. Draw dot and cross held together by electrostatic forces of diagrams to show the attraction formation of ammonia Ionic bonds form between a metal and a non-metal (NH3), water (H2O), The formula of a ionic compound denotes the nitrogen (N2), oxygen (O2) smallest repeating unit and methane (CH4). Each ionic crystal is a giant ionic lattice 3. Explain the difference in Covalent bonding strength between the Molecules formed between two atoms sharing a metallic bond in aluminium pair of electrons and sodium. Use diagrams Bonds usually formed between two non-metals to illustrate your answer. The formula of a covalent compound is the individual molecule 4. Draw a dot and cross Covalently bonded substances can also be diagram to show how MACROMOLECULAR – giant compounds ammonia (NH3) can form a containing many covalent bonds co-ordinate covalent bond with a hydrogen ion (H+). Metallic bonding Positive metal ions surrounded by a sea of 5. Predict the type of electrons bonding formed between The larger the ion the stronger the bond a. copper and chlorine b. sulphur and fluorine Co-ordinate or dative covalent bonds (new for A level) Covalent bond formed between two atoms when both electrons come from one atom 4 Macromolecules are polar liquids and covalently Properties of ionic and covalent compounds not soluble in bonded substances don’t water – you would dissolve. Ionic Bonds have to break many Forces between oppositely charged ions are very strong covalent 5. Which compound will strong bonds have the higher melting The bigger the charge on the ion the stronger the Covalent point? bond macromolecules do a. C5H12 Ionic compounds have very high melting points not conduct b. C10H22 as a lot of energy is required to overcome the electricity – Explain your reasoning. forces of attraction exception - Ionic compounds are soluble in water because it is graphite 6. Which compound has a polar molecule the higher melting point? Ionic compounds do not conduct electricity unless a. NaCl they are MOLTEN – this allows the ions freedom to Questions b. MgCl2 move Explain your reasoning 1. Explain how adding salt Covalent Bonds to water allows it to The covalent bond itself is very strong conduct electricity The intra-molecular forces between molecules are very weak and therefore not a lot of energy is 2. Draw the structure of needed to overcome them – low melting points diamond and graphite. Intra-molecular forces increase with mass Explain how graphite is Covalent molecules are non-polar and not able to conduct electricity. soluble in water – they are soluble in other non- polar liquids 3. Explain how you could Covalent molecules do not conduct electricity – distinguish between there are no free electrons to carry the current identical looking crystals if you knew that one crystal Giant covalent molecules - Macromolecular was ionic and one Made up of strong covalent bonds – a lot of energy macromolecular covalent. is required to break these bonds – they have very high melting points 4. Explain why ionic compounds can dissolve in
5 The Periodic Table If you learn this you will these elements? Kr, always know the charge of Ne, F, Li, Cu, Zn, Mn The periodic table will always be given out in an a common ion. exam and it is full of useful information Questions Columns are known as GROUPS – they are families of elements with similar chemical properties 1. Write down the Rows are known as PERIODS – elements exhibit atomic number of periodic behaviour these elements. Na, The larger number on the table is the MASS B, At, W number – the total number of protons and neutrons added together 2. Write the down the The smaller number on the periodic table is the mass number of ATOMIC number – this is the number of protons these elements. Ca, contained in that particular atom F, K, As The periodic table also tells you the symbol of each atom 3. Calculate the number of neutrons You can also use the periodic table to work out the in these elements. electronic structure of the elements and the number of Ge, H, I, V ions present As you go from left to right on the periodic table you can 4. What period are work out the charge of the most common ions these elements in? F, Cs, Au, He Miss out the middle + + + +/- -3 -2 - 0 5. What is the charge 1 2 3 4 1 on the following ions? Br, Sr, Rb, S, Xe, Ge, Sb
6. What is the electronic configuration of
6 Energy, rates of reaction (kinetics)
Energy is transferred during chemical reactions. 1. In a reaction between When energy is transferred into reactions limestone and hydrochloric overall the reaction is said to be endothermic acid which form of and the surroundings cools down (reaction feels limestone would you use colder). for the fastest rate? When energy is transferred to the surroundings Powdered, small chips, from the reaction it is called exothermic and the large lumps. surroundings heat up (reaction feels hotter). Reaction rate is a measure of how fast the 2. When how would you reaction takes place in a given amount of time. stop a reaction from going You can measure changes in pH, colour, volume to fast because it produces of gas produced, change in mass etc to give a excess heat. rate. 4 factors affect the rate of reaction. 3. Sketch a graph of Surface area, temperature, concentration of volume of gas made reactants, addition of a catalyst. against time. Label the You should be able to recall how these factors areas with the fastest and can be used to increase or decrease rates of slowest rates of reaction. reaction. Yield is used a measure of a reactions success. 4. On the same graph Theoretical yield is a calculation (using moles sketch two other lines to theory) to calculate what the maximum possible show the same reaction yield can be. happening at higher and Actual yield is a measure of how much was lower temperatures than actually made the original reaction. Label Percentage yield is a calculation that expresses accordingly. the actual yield compared to the theoretical yield. 5. Why is it only necessary High yield and fast reaction rates for the lowest to add a small amount of cost are best for chemical industries. catalyst to a reaction? Remember energy cost money!
7 + Reversible reactions and equilibria. ammonia (NH3). So in this SO3(g) + H2O(g) H2SO4(g) case raising the 2) In the reaction Some reactions are reversible. The backwards reaction temperature to increase above what can take place at the same time as the forwards reaction the rate of reaction conditions would under the same reaction conditions. wouldn’t be a good idea. you use to increase the yield of H2SO4 It is important to remember that the reactants and We would say “raising given that the products are in a sealed container. All reactants and temperature moves the forward reaction products will be at the same temperature and pressure. equilibrium to the left as exothermic. this opposes the change These reversible reactions eventually reach a point where (by favouring the 3) In practice in the the RATE of the forwards and backwards reaction will endothermic direction). Haber process the become equal. This means that the relative mixture of ammonia concentrations of reactants and predicts remain Increasing pressure gas and unreacted constant. The reaction has reached dynamic always favour the side of hydrogen is cooled equilibrium. the reaction (equation) that so that the ammonia has the least moles of gas condenses and These reactions can be difficult to control as the ratio or gas. then removed. reactants and products is controlled by picking the correct Explain how this conditions of temperature and pressure. This is done 1) In the example helps the overall according to Le chatalier’s principle which state the above explain the yield of ammonia reaction system will always seek to oppose the change effect of raising increase. applied to it. pressure and lowering pressure on 2HI(g) H2(g) + I2(g) N2(g)+ 3 H2(g) 2NH3(g) the position of 4) In this example equilibrium. above pressure has In the reaction above (the Haber process) the forwards no effect. Explain reaction is known to be exothermic. Raising the why? temperature forces the reaction to oppose that change. This means that the endothermic direction is favoured, this has the result of absorbing the extra heat energy and favours the production of Nitrogen and hydrogen. This has the knock on effect of reducing the concentration on
8 Chemical reactions Part 1. There are many different chemical reactions that can take Or in the case of place. carbonates
+ 2- Making salts. 2H + CO3 H2O + CO2 A salt is the by-product of when acids and bases react together. Here the oxide ion is part Acids are substances that release hydrogen ions (H+) into of the carbonate ion and as solution. These substances dissolve in water to give it a you can see CO2 is pH of less than 7. released. Some acids are described as strong acids- these fully ionise in solution. All of their molecules break up and 1) Write word and symbol produce large numbers of hydrogen ions. E.g. Sulphuric equations for the acid H2SO4 pH 1-2. reactions between Nitric acid and iron (III) Some are described as weak acids e.g. Ethanoic acid oxide CH3COOH. Here only a relatively small number of acid Copper Carbonate and molecules ionise. So the number of H+ ions made is a Sulphuric acid. much smaller and the pH is higher (3-6) Potassium Hydroxide and Hydrochloric acid. Bases are chemicals that can neutralise acids. Alkalis are soluble bases. They release Hydroxide ions 2) Suggest a reaction (OH-) when they dissolve. E.g. Sodium Hydroxide. that will produce A neutralisation reaction is always nickel sulphate.
+ - H + OH H2O
So what about Metal oxides and carbonates? Metal oxides and metal carbonates are bases but are insoluble in water.
Here the Oxide ion itself can react with hydrogen ions to neutralise it. + 2- 2H + O H2O
9 Chemical reaction part 2 Here Iron reduced Copper This will work as long as Reduction/oxidation reactions Part A. oxide. the metal (element) is Actually, we can say the more reactive than the Redox reactions involve the transfer from one thing to Iron atoms reduce the metal already in the another. Cooper ions in the copper compound. oxide. This can be shown Reduction – Gain of electrons by a substance (species) using electron ion 1) Write the chemical Oxidation – Loss of electrons by a substance (species). equations (aka- half equation for the equations, aka ionic displacement of We use the word species at A-level because we want to equation) Silver from silver say specifically what “thing” in a compound is being nitrate (AgNO3) reduced or oxidise. Fe Fe3+ + 3e- using Copper. The iron atoms loos 2) Explain why Remember gain of oxygen is oxidation because oxygen is electrons and forms the Hydrogen gas can good at gaining control of electrons in a compound. Iron (III) ions. be used to extract copper from Copper Displacement reactions are examples of redox reaction Cu2+ + 2e- Cu. oxide (CuO). Use (metal displacement and halogen displacement are the The copper ions in the chemical equations same type of reactions.) copper oxide gain those and half equations electrons and form copper to support your The reactivity of a metal depends on its ability to for a atoms (i.e. copper metal). answer. positive ion. Na is very good, K is even better. Cu is pretty rubbish at it. Fe and Zn sit somewhere in the middle. Notice the electrons appear Carbon also appears in this list as carbon is pretty good at on opposite sides of the reducing most metals. Even Hydrogen crops in the list too, reaction arrow. This is somewhere near the bottom. important for developing this idea further at A level.
Metal displacement reactions. The Fe reaction is the oxidation half equation and Iron + copper oxide Iron (III) Oxide + Copper. the Cu equation is the reduction half equation. 2Fe + 3 CuO Fe2O3 + 3 Cu
10 - - Cl2 + 2e 2Cl reaction does not happen. Displacement reactions part B Halogen/halide These displacement redox. reactions will work as long as the halogen (atom form The halogens are very good oxidising agents. They are of the element) is higher good at stealing electrons form other species and oxidising up the group (smaller the species react with (whilst reducing themselves). atom) than the halide ion (the ionic form). The ability to gain electrons is related to the size of the halogen atom F has only 2 shells, Cl has 3 Br has 4 and I You will see at A level that has 5. As the outer electron shell gets further away from the halogen are used to the nucleus the attraction to gain electrons gets weaker oxidise lots of different and weaker. So F2 is a very strong “gainer of electrons” things (because they are (at A level we would say it is a strong oxidising agent), very good at gaining whilst I2 is much weaker (compared to F2). electrons). One of these is chlorine in bleach. We can study the displacement reactions of the halogens like this. 1) Write the word and symbol equations for 2 KBr + Cl2 Br2 + 2KCl the reaction between Potassium Chlorine is able to gain electrons from the bromide ions. iodide and Fluorine. This means the bromide ions turn back into Bromine 2) Work out the half atoms and pair up. equations involve. 3) Iodine is not able to Again this can be broken down into two half equations displace Chloride showing the movement of electrons. ions form Sodium chloride. Using half - - 2Br Br2 + 2e equations and referring to the sizes Notice here how the number of ions and atoms has to of the atoms, balance. explain why this
11 Oil and hydrocarbons. Alkenes- have at least one cracking. Describe the two C=C bond. This bond could processes and state the Carbon compounds are very special numerous and varied. hold extra hydrogen (or differences in products Hydrocarbons are the simplest and a natural source of other atoms, so it is an produced. these is crude oil. unsaturated hydrocarbon. 3) Draw the first four Homologous series- a family of related chemicals. Short chain alkanes are members of the Organic molecule- molecule based on carbon (and useful as fuels. They are usually hydrogen) volatile and burn well in air Alkane Functional Group- the part of the molecules that is and give out useful Alkene different between one family of molecules and another. amounts of energy. Alcohol Molecular formula- shows the actual number and type Carboxylic acid of atoms in a compound Long chain hydrocarbons, Homologous series. Displayed formula- shows the position of atoms and whilst some are useful as State the family name and bonds in a molecule. fuel such as diesel and highlight the functional heavy fuel oil used in ships, group in each family of A good skill for this area is to quickly recognise functional it doesn’t burn as easily molecules. groups and structures of molecules. Is it an alkane, alkene and so these hydrocarbons or something else? are much lower in demand.
Fractional Distillation separates Hydrocarbons in crude Cracking- A chemical oil in to “fractions” which have similar chain lengths. This process that breaks long is a physical process. chain hydrocarbons in to shorter one and sometimes Hydrocarbons produces Alkenes as well. The chemicals found in crude oil are mainly hydrocarbons. They are a family of molecules made form only hydrogen and carbon. Examples of family members are methane 1) Find a diagram of a ethane and propane. fractional distillation tower. Alkanes- are saturated hydrocarbons, they hold as much Annotate it (labels and hydrogen as possible as there are no double bonds only describe) how crude oil is C-C bonds separated into fractions. 2) Research the use of Cat cracking and thermal
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