Answers. Unit 1 Chemical changes and structure Chapter 1 Rates of reaction 1. Activity 1.1. Activity 1.2. Activity 1.3

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1 Rates of reaction 1 Answers Unit 1 Chemical changes and structure Chapter 1 Rates of reaction 1 Activity (A) and (D): new substances are formed. In (B) and (C) no new substances are formed. 2. (a) Metal went on fire and a green solid was formed. (b) It is toxic (harmful). Activity Use powdered zinc; increase the concentration of the acid; increase the temperature of the acid; add a catalyst. 2. (d) Particle size large small Observations slow fast (e) Small particles react faster than large particles. (f) Weigh out equal masses of large and small lumps. Use a measuring cylinder to measure equal volumes of acid. Collect the gas produced and measure the volume collected over a set time. Activity Ask your teacher to check your report. It should include some of the following: Unprotected iron and steel items slowly rust if they are left exposed to the weather. Milk and other foods are kept cold in a fridge to slow down chemical reactions that cause them to go off. Catalysts are used to speed up important industrial reactions. Air bags in cars rely on explosively fast reactions to inflate them quickly. Cars with petrol engines are fitted with catalytic converters to stop harmful gases getting into the atmosphere. 2. Red: lithium or strontium Green: barium Yellow: sodium Lilac: potassium (continued) 1

2 Chemical changes and structure 3. (a) So that the air bag inflates as quickly as possible so the passengers are protected as soon as a collision occurs. (b) The larger the surface area the more area there is for reactants to come in contact with so the reaction is faster. Chapter 2 Rates of reaction 2 Activity (a) Plan Weigh out powdered zinc. Add to flask. Add a measured volume of acid to flask. Start stop clock. Collect gas by displacement of water or in gas syringe. Note volume of gas collected every minute. Either of the arrangements shown could be used: measuring cylinder gas dilute hydrochloric acid water marble chips gas syringe dilute hydrochloric acid marble chips 2

3 Rates of reaction 2 (b) (i) A (ii) Steeper at A so reaction is faster. (iii) Stopped. (c) 30 cm 3 (d) (i) Gas volume (cm 3 ) higher temperature lower temperature Time (minutes) (ii) The slope is steeper near the start because the reaction is faster. The final volume of gas is the same because the mass of chalk reacting is the same. (e) 34 cm 3 2. (a) Plan Weigh out powdered zinc. Add to flask. Add a measured volume of acid to flask. Place on balance and note reading. Start stop clock. Note mass every minute. Diagram of experimental arrangement loose cotton wool plug to stop spray escaping dilute hydrochloric acid marble chips balance laptop printer (b) (i) X (ii) Powdered chalk reacts faster than lumps so graph will have a steeper slope. (c) 1.6 min (d) 0.8 g (e) The same mass of chalk reacts. (f) The slope of the graph would be steeper. 3

4 Chemical changes and structure Activity 2.2 Ask your teacher to check your plan. It should include the following, but will not be exactly the same. Plan Weigh out magnesium ribbon (your teacher will tell you how much to use if you do the experiment). Add to flask. Add a measured volume of acid to flask (your teacher will tell you what volume to use if you do the experiment). Start stop clock. Collect gas by displacement of water or in gas syringe. Diagram of experimental arrangement Either of the arrangements shown could be used: measuring cylinder gas dilute hydrochloric acid water marble chips gas syringe dilute hydrochloric acid marble chips Measurements to be taken Volume of gas collected (cm 3 ) every minute. 4

5 Chemical structure Recording and presenting results The results should be presented in a table like the one shown: Time (min) Volume of hydrogen collected (cm 3 ) etc. Chapter 3 Chemical structure Activity Solid, liquid and gas. 2. (a) (i) water (ii) ethanoic acid (iii) vinegar (b) A solution in which no more solute can dissolve. Activity (a) atom (b) elements (c) joined (d) mixture (e) separated (f) easily (g) electricity 2. (a) A and D (b) C (c) B 3. (a) Magnesium fluoride (b) Zinc chloride (c) Sodium sulfide (d) Lead oxide 4. sodium + fluorine sodium fluoride zinc + oxygen zinc oxide lead + bromine lead bromide magnesium + nitrogen magnesium nitride 5. (a) magnesium + fluorine magnesium fluoride (b) zinc + chlorine zinc chloride (c) sodium + sulfur sodium sulfide (d) lead + oxygen lead oxide 5

6 Chemical changes and structure Activity (a) (i) Filtration (ii) Evaporation (b) Distillation: a method of separating a mixture of liquids. Boiling point: the temperature at which a liquid becomes a gas or a gas becomes a liquid. 2. (a) Both insoluble. (b) It would not work. (c) One of the salts has to be soluble and the other insoluble. 3. Your plan should include: (a) Filter the mixture the sand is trapped in the filter paper and the salt solution drips through into a beaker or flask. (b) Heat the salt solution in a dish until most of the water evaporates; leave the rest of the water to evaporate at room temperature; salt crystals will form. 1. Activity 3.4 Separation technique filtration distillation Everyday examples filter coffee clean drinking water making whisky fractional distillation of oil desalination of seawater 2. (a) Country World daily production of desalinated water (%) Saudi Arabia 18 UAE 14 USA 14 Spain 8 Kuwait 6 Algeria 5 China 5 Qatar 4 Japan 2 Australia 2 (b) Saudi Arabia is in the Middle East, which is very dry there are large areas of desert and little or no rain. (c) Scotland gets its drinking water from rain, of which there is normally a plentiful supply. 6

7 Chemical structure Activity (a) The periodic table (b) (i) Left; right (ii) Group 2. (a) Place the substance to be tested between the crocodile clips. (b) The bulb would light. (c) (i), (iii), (iv), (vi), (vii) (d) They are metals. (e) (i) Ag (ii) S (iii) Sn (iv) Ca (v) Si (vi) Zn (vii) Ni (f) Graphite is a form of carbon, so is a non-metal, and non-metals generally don t conduct electricity. 3. (a) (i) Y (ii) Metals are conductors of electricity. (b) (i) Y (ii) X (iii) Z (c) (i) Alkali metals (ii) Halogens (iii) Noble gases (d) Bromine; Br 4. Helium is very unreactive. 1. Activity 3.6 Element Symbol Atomic number indium In 49 gallium Ga 31 rhenium Re 75 arsenic As 33 selenium Se 34 chromium Cr 24 niobium Nb 41 tungsten W 74 molybdenum Mo (a) The metals are very rare and they are not always available from the countries where they can be found. (b) Recycle and reuse them. 7

8 Chemical changes and structure 1. (a) Activity 3.7 K I K I KI (b) Ba S Ba S BaS (c) Mg Mg Mg 2 (d) Br Br Al Al AlBr 3 Br Br Br Br 2. (a) NO (b) SO 2 (c) SO 3 (d) C 4 (e) P 5 Chapter 4 Atomic structure and bonding related to properties of materials Activity (a) (a) protons (b) (n) (c) electrons (b) (d) neutrons (e) nucleus (f) electrons (g) positive (h) 1 (i) no (j) negative (k) zero electron proton neutrons 8

9 Atomic structure and bonding related to properties of materials 2. (a) (a) Li (b) 3 (c) 3 (d) 3 (e) 7 (f) chlorine (g) (h) 17 (i) 17 (j) 18 (k) neon (l) Ne (m) 10 (n) 10 (o) 21 (b) There are the same number of positive and negative particles in an atom so they balance each other s charge. Activity (a) non-metal (b) diatomic (c) Water 2. (c) (i) F F (ii) P F F P Activity (a) (i) (ii) H F H F (b) and H F (c) Covalent 9

10 Chemical changes and structure Activity (a) K (b) 19 (c) Loses 1e (d) 18 (e) Oxygen (f) 8 (g) O 2 (h) (a) Ionic (b) The lithium atom gives an electron to the chlorine atom. A positive lithium ion and a negative chlorine ion are formed. The positive and negative ions attract each other forming an ionic bond. Li Li + non-metal positive atom ion metal atom 1e 3. (a) Ionic (b) Ionic (c) Covalent (d) Covalent negative ion Activity (a) Gas (b) Liquid (c) Solid (d) Gas (e) Solid (f) Solid 2. (a) A is covalent; B is ionic. (b) Neither covalent nor ionic substances conduct electricity when solid. When they are dissolved in water or in the liquid state ionic substances conduct but covalent still don t. 3. All compounds are electrical insulators when solid, so the student s conclusion is not valid. The calcium chloride should be dissolved in water or melted and re-tested. It will conduct when in solution or melted (liquid) so it must be ionic. Activity (a) Mg (b) P (c) H 2 (d) O 2 2. (a) Sodium, nitrogen and oxygen (b) Aluminium, sulfur and oxygen (c) Calcium, carbon and oxygen (d) Potassium, nitrogen and oxygen (e) Magnesium, sulfur and oxygen (f) Lithium, hydrogen, carbon and oxygen 10

11 Atomic structure and bonding related to properties of materials Activity (a) Na 3 N (b) Al 2 O 3 (c) CaS (d) BP 2. (a) Si 4 (b) Si 2 H 6 (c) C 4 H 10 (d) C 3 H 6 (e) CH 4 3. (b) (i) H H (ii) S (iii) Si H H or H Si H H H H H N or N (iv) H H H C C H H or H H C H H S H Activity (a) 160 (b) 46 (c) 95.5 (d) (a) As the relative atomic mass increases the melting point decreases. (b) Lower than 39 ºC. 3. (a) 28 (b) 56 (c) 36.5 (d) 34 (e) Activity (a) Na + O 2 Na 2 O (b) Al + 2 Al 3 (c) N 2 + H 2 NH 3 (d) Li + Br 2 LiBr 2. (a) mercury + sulfur mercury sulfide (b) Hg + S HgS (c) Hg (l) + S (s) HgS (s) 11

12 Chemical changes and structure Chapter 5 Energy changes of chemical reactions Activity (a) (i) Exothermic (ii) Taken in from (b) (i) Burning (combustion); acid reacting with alkali (neutralisation) (ii) Photosynthesis 2. (a) (i) Reaction 1: exothermic; reaction 2: endothermic; reaction 3: exothermic (ii) Reaction 1: increase in temperature; reaction 2: decrease in temperature; reaction 3: increase in temperature (b) (i) Experiment 1 (ii) Greater increase in temperature in experiment 1 than in experiment 3 3. Plan and report should include these points: temperature measured temperature measured temperature measured thermometer thermometer thermometer plastic beakers mix plastic beaker nitric acid potassium hydroxide solution solution Equal volumes of the two solutions should be used. The temperature of each solution should be measured before mixing. The highest temperature reached when the solutions are mixed should be recorded. The most accurate results are obtained when the volumes of solution are measured using a measuring cylinder and plastic beakers are used to reduce heat loss to the surroundings. If the solutions are at different temperatures before they are mixed, then the temperatures should be averaged. 4. (a) The explosions could have been caused by calcium carbide reacting with water to produce a flammable gas called ethyne. The ethyne may then have exploded and also caused another chemical, ammonium nitrate, to explode. (b) Calcium carbide is used to make ethyne, which, in turn, is used to make polyvinyl chloride (PVC), a very useful plastic. Locally produced ethyne made from calcium carbide is more economical than using imported oil. China also has lots of coal, a source of calcium carbide, which is much cheaper than oil. (c) (i) calcium carbide + water calcium hydroxide + ethyne (ii) Calcium and carbon (d) Oil 12

13 Acids and bases 1 Chapter 6 Acids and bases 1 Activity (g) Solution tested Colour change Acid or alkali? vinegar purple pink acid lemon juice purple pink acid bicarbonate of soda purple blue alkali milk of magnesia purple blue alkali (h) Use a syringe to accurately measure the volume of solution being tested and add the same number of drops of indicator to each test tube. 2. (a) Solution A, B, C or D ph caustic soda D 14 citric acid B 3 milk of magnesia C 11 hydrochloric acid A 1 (b) Hydrochloric acid (c) Caustic soda (d) (i) ph 7 (ii) Lime green 3. (a) 1 day (b) 3 days (c) (i) More acidic (ii) The ph is dropping. The lower the ph, the more acidic the solution. (d) = (a) Adding more water dilutes the water already in the pool so the ph will move up towards ph 7. (b) (i) Alkaline (ii) Take a sample of the water. Add universal indicator. Compare the colour with the colours on the chart and the corresponding ph number. 5. (a) Dilute (b) Up (c) Down 13

14 Chemical changes and structure Activity Your report should include: (a) one acid and its source from Table 6.3 (on page 81) (b) oxalic or benzoic acid; possible kidney damage and irritation/inflammation in the body (c) one acid from Table 6.4 (on page 81) added as preservative/to give sharper flavour 2. Carbon dioxide gives drinks their fizz. Carbon dioxide is acidic and so drinking too much can cause tooth decay. Activity (a) ph rises towards 7 (b) Use universal indicator and note the colour change. Match colour with ph chart. (c) Neutralisation (d) ph falls towards 7 2. Sarah is correct because water is formed in a neutralisation reaction not hydrogen. 3. (a) calcium hydroxide + sulfuric acid water + calcium sulfate (b) magnesium hydroxide + hydrochloric acid water + magnesium chloride (c) sodium hydroxide + nitric acid water + sodium nitrate 1. Activity 6.4 Situation indigestion mouth acid acid spillage acid soil acid waste from factories bee sting Neutralised by antacids (magnesium hydroxide) saliva and toothpaste bicarbonate of soda lime slaked lime (calcium hydroxide) sodium hydrogencarbonate 2. (a) (i) Hydrochloric acid is in the stomach. (ii) Stomach acid can have a ph as low as 1. (b) (i) Acid-ease (ii) It reduced the acidity the most in the fastest time. (c) (i) The reaction would be speeded up it would take less time for the antacid to react. (ii) The colour change would be the same. 14

15 Acids and bases 1 Activity (a) (i) Carbon dioxide, sulfur dioxide and oxides of nitrogen (ii) Burning fossil fuels (b) (i) Burn less fossil fuels (ii) Scrub the waste gases 2. (a) Soluble acidic gases released into the atmosphere dissolve in the droplets of rain water. (b) Any one from: trees and even forests can be killed damaged leaves can t photosynthesise efficiently buildings and bridges have been damaged. (c) Add lime (calcium carbonate). 3. (a) Carbon dioxide is taken out of the atmosphere. (b) (i) The oceans are becoming more acidic (less alkaline). (ii) Animals with shells find it harder to make the shells. 4. ph decreases 5. Student s own answer. Activity (a) (i) Carbon dioxide (ii) Greater levels of greenhouse gases prevent more heat from Earth escaping into space, so Earth s temperature is rising. (iii) Global warming (b) (i) Global warming may be causing climate change. (ii) Any one from: melting of polar ice sheets, causing sea levels to rise and low-lying areas to be flooded some areas will have less water for drinking and for growing food tropical diseases like malaria spreading over a wider area more frequent severe weather events. 2. (a) (i) Increasing (ii) The Industrial Revolution occurred after 1860 when factories began to release more carbon dioxide into the atmosphere. (b) Increasing 15

16 Chemical changes and structure Chapter 7 Acids and bases 2 Activity (a) (i), (ii) and (iv) (b) (i) and (ii) because they are soluble in water (c) (i) Any one of the following carbonates: lithium, potassium or sodium (ii) Any one of the following oxides: magnesium, nickel or zinc 2. (a) potassium oxide + sulfuric acid water + potassium sulfate (b) lithium hydroxide + hydrochloric acid water + lithium chloride (c) nickel carbonate + nitric acid water + nickel nitrate + carbon dioxide (d) calcium carbonate + sulfuric acid water + calcium sulfate + carbon dioxide 3. Plan Chemicals needed: hydrochloric acid, sodium hydroxide and universal indicator. Diagram of experimental arrangement burette dilute acid conical flask dilute alkali and universal indicator Steps: Add alkali to a conical flask. Add universal indicator to the flask. Add acid to a burette. Run the acid into the conical flask. Stop adding acid when the indicator turns lime green. 4. Solid zinc carbonate would be seen in the flask and no more bubbles of carbon dioxide gas would be seen. 16

17 A acids and bases 2 Activity Burning fossil fuels and cement production. 2. Student s own answer. 3. (a) A carbon footprint is a measure of the impact that all our activities have on the environment. (b) Compared with people in the US and the UK, people in developing countries might: use less energy to heat homes use fewer electrical appliances travel shorter distances eat less meat and more locally produced vegetables. 4. (a) (i) Wind power (ii) Electricity produced from wind does not involve burning fossil fuels. (b) Region Reduction in greenhouse gas emissions (%) Scotland 39.5 England 34.0 UK 33.0 Sweden

18 Chemical changes and structure Unit 1 practice assessment National 3 1. Bright flame seen or white solid seen 1 2. One of: increasing the temperature of the reaction mixture or the concentration of the reactants or the surface area of the reactants, or adding a catalyst 1 3. No new substance is formed 1 4. Solute 1 5. (a) B and C (calcium and magnesium) 1 (b) D (nitrogen) 1 (c) A (sodium) 1 6. A (graphite) 1 7. (a) AlI 3 1 (b) aluminium + iodine aluminium iodide 1 (c) Filtration 1 8. (a) Any number less than 7 1 (b) Red (pink/orange/yellow) 1 (c) Sodium chloride 1 9. (a) ph goes up 1 (b) Neutralisation (a) ph goes down 1 (b) Contributes to tooth decay (a) Burning fossil fuels 1 (b) Gases are soluble and dissolve in rain water to make it acidic 1 (c) Animals with shells have difficulty growing them 1 Total 21 National 4 1. (a) (i) Experiment 2 1 (ii) The particle size is smaller 1 (b) (i) 225 s 1 (ii) 0.55 g 1 2. (a) (i) Experiment A has a steeper slope than experiment B. 1 (ii) Use more dilute acid or lower the temperature of the original acid. 1 (b) Bubbled through water into a measuring cylinder or collected in a gas syringe. 1 18

19 Unit 1 practice assessment 3. (a) Nucleus 1 (b) (i) 9 1 (ii) There are the same number of protons (positive) and electrons (negative) so their charges balance each other 1 (c) Beryllium 1 4. (a) 1 (b) Calcium, chlorine and oxygen 1 5. Y 1 6. (a) (b) Ionic 1 (c) Ca + 2 Ca Heat (energy) is given out to the surroundings Temperature dropped 1 9. (a) (i) Increases 1 (ii) No effect 1 (b) The other non-metal oxides in the table are soluble and decrease the ph of water 1 (c) Potassium hydroxide or potassium carbonate As preservative (a) Neutralisation 1 (b) (i) Copper sulfate 1 (ii) A salt 1 (c) Some copper carbonate would be left in the beaker or no more bubbles of gas (carbon dioxide) would be seen 1 (d) Cement manufacture 1 Total 29 19