C3 Revision Pack (Please keep this pack with you)

Transcription

1 Name: C3 Revision Pack (Please keep this pack with you) Follow all the steps below... 1) Practice all the maths and working scientifically questions PRACTICE ALL THESE QUESTIONS! Maths and Science Skills Questions Standard Questions Higher Questions - 2) Practice Quiz short answer questions (included in this pack) 3) Practice QWC questions long answer questions (included in this pack) 4) Practice all the Popplet questions C3.1 The periodic table C3.2 Water C3.3 Energy change C3.4 Further analysis and quantitative chemistry C3.5 The production of ammonia C3.6 Alcohols, carboxylic acids and esters Standard Demand Higher Demand Standard Demand Higher Demand Standard Demand Higher Demand Standard Demand Higher Demand Standard Demand Higher Demand Standard Demand Higher Demand Our Predictions: Experiments and graphs are a BIG part of this paper - Practice the maths and working scientifically questions above! o Don t forget to reference the data when describing/explaining graphs o Identify changes in graph look at how many marks and use this as guidance for how much detail you need to give Testing for ions Organic chemistry Ethics, e.g. changes in periodic table, water Trends in reactivity within periodic table Water, e.g. scum, scale, ethics about what government puts in water Energy level diagrams Equilibrium Flame tests Ammonia Titration calculations, bond enthalpy calculations, calorimetry calculations and bond enthalpy calculations Revise everything in detail as they are likely to throw something new at you and you will have to apply your knowledge to it.

2 PRACTICE QUIZ GCSE Chemistry 3 Summary Questions and Answers C3.1.1 The early periodic table Q1 Explain Newlands law of Octaves. A1 - He arranged all the elements known at the time into a table in order of relative atomic mass. - Newlands' table showed a repeating or periodic pattern of properties, but this pattern eventually broke down. - By ordering strictly according to atomic mass, Newlands was forced to put some elements into groups which did not match their chemical properties. Q2 Explain why Newlands law was criticised. A2 - His groups contained elements that didn t have similar properties - Non-metals and metals were mixed - He didn t leave any gaps for elements that hadn t been discovered yet. Q3 Explain why Mendeleev was much more successful than Newlands. A3 - He recognised that there were some elements still to be discovered, so he left gaps in his table. - He was not afraid to change the order of some elements in the table where it seemed to make sense. - He was able use the table to successfully predict the properties of some elements which had not yet been discovered. Q4 C3.1.2 The modern periodic table How are the elements in the periodic table arranged? A4 - Elements in the periodic table are arranged in order of atomic number (number of protons in the nucleus). - Elements in the periodic table are also arranged by their electronic structure. Q5 How are the electrons in an atom set out? A5 - Electrons in an atom are set out in shells which each correspond to an energy level.

3 Q6 What is the group number equal to? A6 - The group number is equal to the number of electrons in their highest occupied energy level. Q7 What is the period number? A7 - The period number is the same as the number of occupied energy levels. Q8 C3.1.3 Trends within the periodic table As you go down Group 1, what is the trend in reactivity? A8 - Elements become more reactive because the outer electron is more easily lost, since it is further away from the nucleus - Elements have lower melting and boiling points. Q9 What properties do Group 1 elements have in common? A9 Q10 The elements in Group 1 of the periodic table (known as the alkali metals): - are metals with low density (the first three elements in the group are less dense than water) - react with non-metals to form ionic compounds in which the metal ion carries a charge of +1.The compounds are white solids that dissolve in water to form colourless solutions - react with water, releasing hydrogen - form hydroxides that dissolve in water to give alkaline solutions Explain why there is an increase in reactivity going down Group 1. [H] A10 - This is because the atoms lower down have more inner shells of electrons. - These 'shield' the outer electrons from the attraction of the nucleus, and allow the outer electron to be lost more easily. - Since metals react by losing electrons, they become more reactive. Q11 As you go down Group 7, what is the trend in reactivity? A11 - Elements become less reactive because it is more difficult to gain an extra electron, since the outer shell is further from the nucleus. - Elements have higher melting and boiling points. Q12 What properties do Group 7 elements have in common? A12 Q13 The halogens have the following properties in common: - they are non-metals - they have low melting and low boiling points - they are brittle when solid - they are poor conductors of heat and electricity - they have coloured vapours - their molecules are diatomic (each contain two atoms) Explain why there is an increase in reactivity going down Group 7. [H] A13 - The electrons become less reactive as we go down the group because the outermost electron shell gets further away from the influence of the nucleus. - Due to shielding, an electron is less easily gained. Q14 What are halides? A14 - The halogens form 1 - ions called halides when they bond with metals. Q15 A15 The halogens are all non-metals with coloured vapours. Describe the colour of each iof the following and state how reactive they are. (a) Fluorine (b) Chlorine (c) Bromine (d) Iodine (a) Fluorine is a very reactive, poisonous yellow gas. (b) Chlorine is a fairly reactive, poisonous dense green gas. (c) Bromine is a dense, poisonous, red-brown volatile liquid. (d) Iodine is a dark grey crystalline solid or a purple vapour.

4 Q16 Fill in the blank: A more reactive halogen can a less reactive halogen from an aqueous solution of its salt. A16 - displace Q17 Describe the properties of transition metals. A17 - They re good conductors of heat and electricity. - They are very dense, strong and shiny. - Transition metals are much less reactive than Group 1 metals and so do not react as vigorously with water or oxygen. - Compared to Group 1 metals, they have higher melting points (except for mercury) and higher densities. Q18 What colours do the transition compounds have: (a) Potassium chromate (b) Potassium manganite (c) Copper (II) sulphate A18 (a) Yellow (b) Purple (c) Blue Q19 Explain how iron, manganese oxide and nickel are useful as catalysts. A19 - Iron is the catalyst used in the Haber process for making ammonia. - Manganese oxide is the catalyst used for the decomposition of hydrogen peroxide. - Nickel is useful for turning oils into fats for making margarine. Q20 What can soft water form? C3.2.1 Hard and soft water A20 - Lather Q21 What can hard water form? A21 - Scum - Scale Q22 Which dissolved substances does hard water contain? A22 - Calcium ions/ Ca 2+ - Magnesium ions/ Mg 2+

5 Q23 What are the advantages of hard water? A23 - Using hard water can increase costs as more soap is needed - Hard water is good for the development and maintenance of bones and teeth - Hard water can help to lower the risk of heart disease - Hard water can improve the taste of water Q24 What are the disadvantages of hard water? A24 - More soap is needed to produce lather, which increases costs. This happens with temporary or permanent hardness. - Temporary hardness can reduce the efficiency of kettles and heating systems. This is because limescale (a solid containing calcium carbonate) is produced when the water is heated. - The scum produced is unsightly - spoiling the appearance of baths and shower screens, for example. Q25 What is the difference between temporary hard water and permanent hard water? A25 Q26 A26 Q27 Permanent hard water remains hard when it is boiled. Temporary hard water is softened by boiling. What causes temporary hard water to be softened by boiling? Which compound decomposes within temporary hard water? [H] Temporary hard water contains hydrogencarbonate ions (HCO 3- ) that decompose on heating to produce carbonate ions which react with calcium and magnesium ions to form precipitates. Why does using hard water increase costs? A27 - More soap is needed to get a lather OR limescale formed on elements of appliances. Q28 What causes the efficiency of heating systems and kettles to be reduced when hard water is heated in kettles? A28 - Limescale build up (calcium carbonate) reduces efficiency of the heating element. Q29 Write down the word equation that demonstrates the formation of calcium hydrogencarbonate. A29 - Calcium hydrogencarbonate calcium carbonate + water + carbon dioxide Q30 Hard water can be made soft by removing the dissolved calcium and magnesium ions. Describe the TWO methods in which this can be done. A30 - Adding sodium carbonate, which reacts with the calcium and magnesium ions to form a precipitate of calcium carbonate and magnesium carbonate. - Using commercial water softeners such as ion exchange columns containing hydrogen ions or sodium ions, which replace the calcium and magnesium ions when hard water passes through the column. C3.2.2 Purifying water Q31 Fill in the blanks: Water of the correct quality is essential for life. For humans, drinking water should have sufficiently levels of and. A31 - low, dissolved salts, microbes

6 Q32 In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Explain the stages needed in order to make water clean to drink. (6 marks) A32 - Screening o As the water enters the water treatment works, it passes through a screen. o This is made from bars of metal placed together. o These catch large objects such as leaves and twigs. - Settlement Tank o Sand and soil settle out - Adding aluminium sulphate and lime to water o Makes particles of dirt clump together and settle. - Filter (bed) o Fine sand filters remaining particles (insoluble solid) - Chlorination o Water may contain some harmful bacteria. o Therefore adding chlorine kills the bacteria. - Arrival of water to buildings o The ph of the water is checked and corrected so that it is neutral o It is then stored in large tanks and service reservoirs ready to be pumped to homes, schools, offices, factories etc. Q33 Discuss the advantages and disadvantages of adding chlorine and fluoride to drinking water. A33 - Fluorine helps to reduce tooth decay. - Chlorine is added to prevent disease. - Some studies have linked adding chlorine to water with an increase in certain cancers. - Chlorine can react with other natural substances in water to produce toxic by-products which some people think could cause cancer. - In high doses, fluoride can cause cancer and bone problems in humans. - There is a concern about whether it is right to mass medicate people can choose whether to use a fluoride toothpaste, but they cannot choose whether their tap water has added fluoride. - Levels of chemicals added to drinking water need to be carefully monitored. Q34 How does an ion exchange work? A34 - Calcium / magnesium ions are replaced for hydrogen / sodium ions Q35 How can totally pure water be produced and why is it used to produce tap water? A35 - Totally pure water with nothing dissolved in it can be produced by distillation. - Distillation involves boiling water to make steam and condensing the steam. - Distilled water is used in chemistry labs. Q36 What are the disadvantages of producing drinking water by distillation? A36 - It is expensive because large amounts of energy are needed to heat the seawater. - It increases the use of fossil fuels - which are non-renewable resources. - Carbon dioxide emissions from burning fossil fuels contribute to global warming. Q37 In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. A37 Explain how you would carry out titration to compare the hardness of water samples. (6 marks) 1. Fill a burette with 50cm 3 of soap solution. 2. Add 50cm 3 of the first water sample into a flask. 3. Use a burette to add 1cm 3 of soap solution to the flask. 4. Put a bung in the flask and shake for 10 seconds. 5. Repeat steps 3 and 4 until a lasting lather (bubble cover the surface for at least 30 seconds) is formed. 6. Record how much soap was needed to create a lasting lather 7. Repeat steps 1 to 6 with the other water samples. 8. Boil, fresh samples of each type of water for 10 minutes, and repeat the experiment.

7 Q38 C3.3.1 Energy from reactions Explain how fuel energy is calculated using a calorimeter. A38 Q39 A39 Q40 A40 Q41 1. Put 50g of water in the copper can and record its (starting) temperature. 2. Heat the water using the flame from the burning fuel 3. Record the final temperature of the water. 4. Weight the spirit burner and lid again. Describe how you would carry out the energy changes for neutralisation reactions or for reactions of solids with water. To do this experiment: 1. Add a known volume of the first reactant (in solution) to the insulated container 2. Record the starting temperature of the liquid 3. Add the second reactant (either in solution or as a solid powder) 4. Replace the lid and stir the reaction mixture 5. Record the maximum temperature that the reaction mixture reaches What formula can used to calculate the amount of energy transferred during a chemical reaction? You must state the meaning of the letter and the unit(s) used. Q = mc ΔT - Q = the heat energy transferred (joule, J) - m = the mass of the liquid being heated (grams, g) - c = the specific heat capacity of the liquid (joule per gram degree Celsius, J/g C) - ΔT = the change in temperature of the liquid (degree Celsius, C) 50 cm 3 of an acid was added to 50 cm 3 of an alkali. The mixture was stirred and the temperature increased from 18 C to 28 C. What was the amount of energy released in J? (3 marks) A41 - Step 1: Calculate the temperature change, ΔT o = 10 C - Step 2: Use Q = mc T o o o Remember that c = 4.2 J/g C for liquids (unless you are told otherwise): Q = mc T Q = ( ) = 4200 J

8 Q42 In an experiment, ethanol was burnt from a spirit burner and the energy released was used to heat 50 g of water. The starting temperature of the water was 19 C but by the end of the reaction, the temperature had risen to 41 C. The mass of fuel in the spirit burner was initially 40.0 g, but this had decreased to 38.5 g by the end of the reaction. Calculate the energy change in kj/g of fuel. (5 marks) A42 - Step 1: Calculate the temperature change, ΔT o = 22 C - Step 2: Use Q = mc T o Remember that c = 4.2 J/g C for liquids (unless you are told otherwise): o Q = mc ΔT o Q = = 4620 J o Q = 4.62 kj - Step 3: Calculate the mass of fuel burnt o = 1.5 g - Step 4: Divide energy released by mass of fuel burnt o Energy change = = 3.08 kj/g Q43 A43 What happens to the bonds of both products and reactants during a chemical reaction? During a chemical reaction: - bonds in the reactants are broken - new bonds are made in the products Q44 What does an exothermic reaction show? In some parts of your answer, you may need to refer to energy level diagrams. A44 - Exothermic reactions give out heat energy to the surroundings. Q45 - This means that energy is being lost so the products have less energy than the reactants. What does an endothermic reaction show? In some parts of your answer, you may need to refer to energy level diagrams. A45 - Endothermic reactions absorb heat energy from the surroundings, making the temperature of the surroundings cooler. - This means that energy is gained, so the products have more energy than the reactants. Q46 Label the energy level diagram of figure 1, an exothermic reaction and figure 2, an endothermic reaction. Figure 1 Figure 2 A46 Figure 1 1- reactants, 2- products, 3- energy, 4- progress of reaction, 5- released Figure 2 1-reactants, 2- products, 3- energy, 4- progress of reaction, 5-absorbed

9 Q47 Figure 3 Label figure 3, showing the energy changes in chemical reactions. A47 1-activation energy, 2- overall change in energy ( H), 3- products, 4- reactants Q48 Study figure 3. Explain what is meant by number 1 on the diagram. A48 - Activation energy represents the minimum energy needed by reacting particles to break their bonds. Q49 Draw figure 3 and show on the diagram how a catalyst may have an effect. A49 Q50 Describe the advantages of lowering the activation energy. A50 - Lowering the activation energy has many advantages. - It means that reactions happen more quickly and are more economical in terms of the energy required for industrial-scale reactions. Q52 Describe the TWO ways in which hydrogen is used to power cars. A52 - Burning hydrogen directly in the engine o Hydrogen gas can be burnt in oxygen as a fuel in the combustion engines of vehicles. o hydrogen + oxygen water - Hydrogen fuel cells o In a hydrogen fuel cell, hydrogen reacts with oxygen without burning. o The energy released is used to generate electricity, which is used to drive an electric motor.

10 Q53 Discuss the advantages and disadvantages of hydrogen as a fuel. A53 Advantages Disadvantages - unlike petrol and diesel, hydrogen - few filling stations sell hydrogen does not generate carbon dioxide when burnt - hydrogen must be compressed and liquefied, and then stored in tough, - hydrogen fuel cells are very efficient insulated fuel tanks - atmospheric pollution may be generated during the production of hydrogen - hydrogen fuel cells do not work at very low temperatures, and they may also require a platinum catalyst (platinum is expensive and prone to contamination by impurities) Q54 Evaluate the use of fuel cells. A54 Advantages Disadvantages - Reduces pollution caused by burning fossil fuels, the only by product is water - Production, transportation, distribution and storage of hydrogen is difficult - Have a higher efficiency than diesel or gas engines - Driving range of cars is shorter than in a traditional vehicles - Maintenance is more simple - less moving parts in the system - Refuelling and starting times of fuel cell vehicles are longer - Currently expensive to produce, uses some use expensive materials, e.g. platinum C3.4.1 Analysing substances Q55 Complete the table below showing the metal ion and the colour the flame goes. METAL ION FLAME COLOUR Lithium Sodium Potassium Calcium Barium A55 METAL ION FLAME COLOUR Lithium Crimson Sodium Yellow Potassium Lilac Calcium Red Barium green

11 Q56 Complete the table below showing the metals ions and the colour the precipitate goes with sodium hydroxide solution. METAL ION PRECIPITATE COLOUR Calcium, Ca 2+ Copper(II), Cu 2+ Iron(II), Fe 2+ Iron(III), Fe 3+ Aluminium, Al 3+ Magnesium, Mg 2+ A56 METAL ION PRECIPITATE COLOUR Calcium, Ca 2+ White Copper(II), Cu 2+ Blue Iron(II), Fe 2+ Green Iron(III), Fe 3+ Brown Aluminium, Al 3+ White at first, but then redissolves in excess NaOH to form a colourless solution Magnesium, Mg 2+ White Q57 Describe the test for carbonate ions. A57 - You can test for the prescence of carbon dioxide by bubbling it through limewater. The limewater turns cloudy if carbon dioxide is present. - This can be used to test for carbonate ions since carbonates react with dilute acids to form carbon dioxide. Q58 This question is about halide ions. How would you test for chloride, bromide or iodide ions? A58 - Add dilute nitric acid, followed by silver nitrate solution. Q59 Complete the table, which shows the precipitate formed HALIDE ION PRECIPITATE FORMED COLOUR OF PRECIPITATE and the colour of precipitate of Chloride, Cl the halide ions. Bromide, Br Iodide, I A59 HALIDE ION PRECIPITATE FORMED COLOUR OF PRECIPITATE Chloride, Cl Silver chloride, AgCl White Bromide, Br Silver bromide, AgBr Cream Iodide, I Silver iodide, AgI Yellow Q60 Describe the test for sulphate ions. A60 - Add dilute hydrochloric acid, followed by barium chloride solution. - The presence of a white precipitate of barium sulphate shows the presence of sulphate ions in the solution. Q61 Describe what a titration is. A61 - Titrations are used to determine the volumes of acid and alkali needed to react together to produce a neutral solution. - Titrations are carried out using a piece of apparatus called a burette, along with a suitable indicator. Q61 In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Describe how the titration experiment is carried out. (6 marks) A61 1. Add a known volume of alkali into a conical flask using a pipette. 2. Add a few drops of indicator 3. Pour some acid into a burette, and record the reading. 4. Open the tap, add a small amount of acid and swirl the conical flask to mix 5. Add acid until the solution is neutral as shown by the colour change in the indicator. 6. Repeat three times Q62 What formula is used to calculate the concentration in moles per dm 3? State the units. [H] A62 Concentration (mol/dm 3 ) = number of moles / volume (in dm 3 ) Q63 What formula is used to calculate the concentration in grams per dm 3? State the units. [H] A63 Number of moles = mass (g) / relative formula mass.

12 C3.5.1 Making ammonia Q64 How is ammonia produced? A64 - Ammonia is produced using a reaction between nitrogen and hydrogen called the Haber process. Q65 Describe how nitrogen and hydrogen are obtained. A65 - Hydrogen is obtained by reacting natural gas (mostly methane) with steam, or by cracking oil fractions. - Nitrogen is obtained from the air. Air is 78 per cent nitrogen; nearly all the rest is oxygen. When hydrogen is burned in air, the oxygen combines with the hydrogen - leaving nitrogen behind.

13 Q66 Label the letters on figure 4 of the Haber process. A66 Q67 figure 4 a- nitrogen from air b- hydrogen from natural gas c- compressor d- hydrogen and nitrogen in e- iron catalyst beds f- nitrogen, hydrogen and ammonia out g- cooling tank/condenser h- hydrogen and nitrogen i- liquid ammonia j- ammonia out In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Explain what is happening at each stage of the Haber process. Use the numbers on figure 4 to help you. (6 marks) A67 Stage 1 Having obtained the hydrogen and nitrogen gases (from natural gas and the air respectively), they are pumped into the compressor through pipes. Stage The gases are pressurised to about 200 atmospheres of pressure inside the compressor. 2 Stage 3 The pressurised gases are pumped into a tank containing beds of iron catalyst at about 450 C. In these conditions, some of the hydrogen and nitrogen will react to form ammonia. Stage 4 The unreacted nitrogen and hydrogen, together with the ammonia, pass into a cooling tank. The cooling tank liquefies the ammonia, which can be removed into pressurised storage vessels. Stage 5 The unreacted hydrogen and nitrogen gases are recycled by being fed back through pipes to pass through the hot iron catalyst beds again. Q68 What is a closed system? [H] A68 - A closed system is a system in which no reactants are added and no products are removed. Q69 When a reversible reaction occurs in a closed system, what is reached? [H] A69 - When a reversible reaction happens in a closed system, equilibrium is reached in which the rate of the forward reaction is the same as the backward reaction. Q70 What do the relative amounts of all the reacting substances at equilibrium depend on? [H] A70 - the conditions of the reaction

14 Q71 Fill in the blanks: In a reversible reaction the position of equilibrium depends very strongly on the and surrounding the reaction. [H] A71 - temperature, pressure (any order) Q72 What happens when the temperature increases in a reversible reaction? [H] A72 - If the temperature is increased, the yield from the endothermic reaction increases (and the yield from the exothermic reaction decreases). Q73 What happens when the temperature decreases in a reversible reaction? [H] A73 - If the temperature is decreased, the yield from the endothermic reaction decreases (and the yield from the exothermic reaction increases). Q74 What happens when the pressure is raised in a reversible reaction? [H] A74 - It will encourage the reaction which produces less volume. Q75 What happens when the pressure is lowered in a reversible reaction? [H] A75 - It will encourage the reaction which produces more volume. Q76 Explain why adding a catalyst would not affect the equilibrium position. [H] A76 - Catalysts speed up both the forward and backward reactions by the same amount. - So, adding a catalyst means the reaction reaches equilibrium quicker, but you end with the same amount of product as you would without the catalyst. Q77 Evaluate the conditions used in industrial processes in terms of energy requirements. A77 - Less energy is needed to break bonds in the nitrogen and hydrogen molecules than is released in the formation of the ammonia molecules. - A low temperature favours the production of ammonia but the reaction is slow. - A high temperature would make ammonia form faster (and break down faster). A compromised temperature used is 450 C. - A high pressure favours the production of ammonia but the reaction is expensive. A compromise pressure used is 200 atmospheres. Q78 Describe the conditions used in the manufacture of ammonia to increase the rate of reaction. (4 marks) A78 rate of reaction is increased iron/powder acts as catalyst at higher temperatures at higher pressures any 4 answers for 1 mark each 4

15 Q79 A79 Describe and explain the conditions used in the manufacture of ammonia to increase the yield. (7 marks) yield of ammonia is increased at higher pressure since equilibrium is moved to the right (idea) but there is high cost in manufacturing the plant to withstand very high pressures so optimum* pressure of about 250 atmospheres is used (* just quoting the figures not enough) very high pressure increases safety risk yield of ammonia is increased at lower temperatures since equilibrium is moved to the right but the rate of reaction is reduced at lower temperatures so process becomes uneconomic optimum temperature of about 450oC is used yield of ammonia is increased if the ammonia is removed from the reaction mixture since equilibrium is moved to the right (idea) so ammonia is removed as a liquid after cooling and condensing unreacted nitrogen and hydrogen recycled (credit nitrogen and ammonia because of misprint on the diagram) NB Answers in (b) must clearly relate to yield not to rate (except for the qualification w.r.t. temperature) any 7 points for 1 mark each 7

16 C3.6.1 Alcohols Q80 What are alcohols? A80 - Alcohols are actually a family of organic compounds, all of which contain a OH functional group. Q81 What is the general formula for an alcohol? A81 - C nh 2n+1OH Q82 What properties do the first three alcohols share? A82 - They are colourless liquids that dissolve in water to form a neutral solution - They react with sodium to produce hydrogen and a salt. - They burn in the air, releasing energy and producing carbon dioxide and water. - They are used as fuels and solvents, and ethanol is the main alcohol in alcoholic drinks Q83 What is methylated spirit and describe its use? A83 - Ethanol with chemicals (e.g. methanol) added to it. - It is used to clean paint brushes and as a fuel. Q84 State the formula and draw the structures for the three alcohols. A84 methanol ethanol propanol CH 3OH CH 3CH 2OH C3.6.2 Carboxylic acids CH 3CH 2CH 2OH Q85 What are carboxylic acids? A85 - The carboxylic acids are a homologous series of organic compounds. Q86 What functional group do carboxylic acids share? A86 - Carboxylic acids all contain the same functional group COOH.

17 Q87 What do the names of carboxylic acids end in? A87 - The names of carboxylic acids end in -oic acid eg ethanoic acid. Q88 Complete the table below: CARBOXYLIC ACID NUMBER OF C ATOMS STRUCTUAL FORMULA DISPLAYED FORMULA Methanoic acid Ethanoic acid Propanoic acid A88 CARBOXYLIC NUMBER OF C STRUCTURAL DISPLAYED FORMULA ACID ATOMS FORMULA Methanoic acid 1 HCOOH Ethanoic acid 2 CH 3COOH Propanoic acid 3 CH 3CH 2COOH Q89 Complete the following reaction: ethanoic acid + sodium carbonate + A89 - carbon dioxide + sodium ethanoate Q90 What is vinegar? A90 - Vinegar is an aqueous solution containing ethanoic acid. Q91 How is ethanoic acid formed? A91 - Ethanoic acid is formed from the mild oxidation of the ethanol (which is an alcohol). Q92 How is the formation of ethanoic acid achieved? A92 - The addition of chemical oxidising agents - such as acidified potassium dichromate. - The action of microbes in aerobic conditions (in the presence of oxygen). This happens on a small scale when a bottle of wine is left open and exposed to air. On a commercial scale, it is achieved in a fermenter using acetic acid bacteria. Q93 Describe the properties of carboxylic acids. [H] A93 Carboxylic acids: - dissolve in water to produce acidic solutions - react with carbonates to produce carbon dioxide - react with alcohols in the presence of an acid catalyst to produce esters - do not ionise completely when dissolved in water and so are weak acids - aqueous solutions of weak acids have a higher ph value than aqueous solutions of strong acids with the same concentration Q94 How are carboxylic acids useful in industry? A94 - Carboxylic acids with longer chains of carbon atoms are used to make soaps and detergents. - Carboxylic acids are also used in the preparation of esters. C3.6.3 Esters Q95 What are esters? What functional group do esters share? A95 - Esters are organic compounds formed by the reaction of an alcohol with a carboxylic acid. They have the functional group COO. Q96 What properties do esters have in common? A96 - they are volatile - they are liquids that become vapours easily - they have distinctive fruity smells Q97 How do the properties of esters make them useful in the industry? A97 - These properties make esters very useful as food flavourings, and as perfumes in cosmetics. Q98 How is ethyl ethanoate made? A98 - Ethyl ethanoate is the ester made from ethanol and ethanoic acid. - Sulphuric acid is added to act as a catalyst in the reaction.

18 Q99 What products are formed when ethanol reacts with ethanoic acid? A99 - Ethyl ethanoate and water are formed as a result of ethanol s reaction with ethanoic acid. - This reaction is reversible. Q100 What products are formed when ethanol reacts with ethanoic acid? This time, write a balanced symbol equation. A100 CH 3CH 2OH (aq) + CH 3COOH (aq) CH 3CH 2OOCCH 3(aq) + H 2O (l) Q101 Using your answer to Q100, draw the structural formula for each one. A101 Q102 Complete the table below: Name of alcohol Name of carboxylic acid Name of ester Ethanol Propanoic acid Butanol Methanoic acid Pentanol Ethanoic acid A102 Name of alcohol Name of carboxylic acid Name of ester Ethanol Propanoic acid Ethyl propanoate Butanol Methanoic acid Butyl methanoate Pentanol Ethanoic acid Pentyl ethanoate

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27 QWC 6 MARK QUESTIONS Q1. Hard water can be softened by two different methods. Describe how each method softens water and compare the advantages of these two methods. Method 1: Ion exchange Method 2: Adding sodium carbonate (washing soda) KEY POINTS TO INCLUDE IN YOUR ANSWER: General: hard water contains calcium / magnesium (ions) softening water involves removal of calcium / magnesium (ions). ion exchange: resin contains sodium / hydrogen ions which are exchanged with calcium / magnesium ions resin needs periodic replenishment with sodium ions / hydrogen ions or sodium chloride (disadvantage). increases sodium content of water (if sodium ions used) (disadvantage) easy / quick method to use (advantage) continuous process (advantage). sodium carbonate: sodium carbonate is added to hard water calcium / magnesium ions precipitate out as calcium / magnesium carbonate batch process (disadvantage) leaves a residue of precipitated carbonate in the water (disadvantage) increases sodium content of water (disadvantage) easy method to use (advantage) relatively cheap (advantage).

28 Q2. A group of students had four different colourless solutions in beakers 1, 2, 3 and 4. The students knew that the solutions were sodium chloride sodium iodide sodium carbonate potassium carbonate but did not know which solution was in each beaker. The teacher asked the class to plan a method that could be used to identify each solution. She gave the students the following reagents to use: dilute nitric acid silver nitrate solution. The teacher suggested using a flame test to identify the positive ions. Outline a method the students could use to identify the four solutions. You should include the results of the tests you describe. KEY POINTS TO INCLUDE IN YOUR ANSWER: Test: add (platinum / nichrome) wire (for the flame test). Accept any method of introducing the solution into the flame, e.g. a splint soaked in the solution or sprayed from a bottle Result: the sodium compounds result in a yellow / orange / gold flame or the potassium compound results in a lilac / purple / mauve flame Test: add dilute nitric acid to all four solutions Result: sodium carbonate and potassium carbonate will effervesce or sodium chloride and sodium iodide will not effervesce Test: add dilute nitric acid followed by silver nitrate Result: sodium chloride and sodium iodide produce a precipitate or sodium chloride produces a white precipitate and sodium iodide produces a yellow precipitate

29 Q3. Alcohols are used as fuels. A student plans an experiment to find the energy released per gram of alcohol burned. The student uses the apparatus shown in Figure 2. Describe how the student should do this experiment. You should include any measurements the student should make. Do not describe any improvements to the apparatus. Do not describe how to do any calculations. KEY POINTS TO INCLUDE IN YOUR ANSWER: light ethanol and heat water extinguish ethanol after suitable temperature rise or after a suitable time stir water measure mass / volume of water measure initial temperature of water measure final temperature of water measure temperature rise measure initial mass of ethanol (and burner) measure final mass of ethanol (and burner) measure change in mass of ethanol

30 Q4. A student used the equipment shown to do a titration. Describe how the student should use this equipment to find the volume of sodium hydroxide solution that reacts with a known volume of acid. Include any measurements the student should make. Do not describe how to do any calculations. KEY POINTS TO INCLUDE IN YOUR ANSWER: acid in (conical) flask volume of acid measured using pipette indicator in (conical) flask sodium hydroxide in burette white tile under flask slow addition swirling colour change volume of sodium hydroxide added

31 Q5. Four labels have come off four bottles. Describe and give the results of the chemical tests that you would do to identify which bottle contained which substance. KEY POINTS TO INCLUDE IN YOUR ANSWER: test + result + inference Flame test: yellow / orange Na+ sodium sulphate Add NaOH to remaining 3 samples: no (white) ppt / ammonia NH4+ ammonium sulphate (white) precipitate magnesium ions or aluminium ions add excess NaOH to the 2 samples which gave a (white) precipitate: precipitate dissolves > aluminium sulphate precipitate insoluble > magnesium sulphate Q6. Many hydrocarbons are used as fuels. An energy level diagram is shown for the combustion of the hydrocarbon methane. Describe and explain why the line rises and then falls to a lower level. KEY POINTS TO INCLUDE IN YOUR ANSWER: rises as energy needed for bond breaking (of reactants) called activation energy bond making (to form products) releases energy called exothermic reaction or more energy given out than taken in or releases heat to the surroundings

32 Q7. Ammonia is manufactured from nitrogen and hydrogen. The reaction is shown in the equation below. The diagram shows some details of the manufacturing process. The graph shows the percentage of reacting gases converted into ammonia at different temperatures and pressures. At room temperature and pressure, the reaction is very slow and only a small percentage of the reacting gases is converted to ammonia. Use the information on the diagram and graph to: describe and explain the conditions used in the manufacture of ammonia to increase the yield. KEY POINTS TO INCLUDE IN YOUR ANSWER: yield of ammonia is increased at higher pressure since equilibrium is moved to the right (idea) but there is high cost in manufacturing the plant to withstand very high pressures so optimum pressure of about 250 atmospheres is used very high pressure increases safety risk yield of ammonia is increased at lower temperatures since equilibrium is moved to the right but the rate of reaction is reduced at lower temperatures so process becomes uneconomic optimum temperature of about 450oC is used yield of ammonia is increased if the ammonia is removed from the reaction mixture since equilibrium is moved to the right (idea) so ammonia is removed as a liquid after cooling and condensing unreacted nitrogen and hydrogen recycled