Separate science quantitative chemistry

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Aldous Carroll
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1 Separate science quantitative chemistry Higher revision questions Name: Class: Date: Time: 8 minutes Marks: 79 marks Comments: Page of 28

Etching is a way of making printed circuit boards f computers. Dario Lo Presti/Shutterstock Printed circuit boards are made when copper sheets are etched using iron(iii) chlide solution.

2 Etching is a way of making printed circuit boards f computers. Dario Lo Presti/Shutterstock Printed circuit boards are made when copper sheets are etched using iron(iii) chlide solution. Where the copper has been etched, only plastic remains. (a) Copper is a good conduct of electricity. Explain why. (2) (b) Iron(III) chlide can be produced by the reaction shown in the equation: 2 Fe + 3 Cl 2 2 FeCl 3 (i) Calculate the maximum mass of iron(iii) chlide (FeCl 3 ) that can be produced from.20 g of iron. Relative atomic masses (A r ): Cl = 35.5; Fe = 56. Maximum mass of iron(iii) chlide =... g (3) Page 2 of 28

3 (ii) The actual mass of iron(iii) chlide (FeCl 3 ) produced was 24.3 g. Calculate the percentage yield. (If you did not answer part (b)(i) assume that the maximum theetical mass of iron(iii) chlide (FeCl 3 ) is 28.0 g. This is not the crect answer to part (b)(i).) Percentage yield =...% () (Total 6 marks) 2 This question is about calcium hydroxide. Ancient artwks and monuments can be protected from acid rain if the surface is sprayed with calcium hydroxide nanoparticles. By Svilen Enev (Own wk) [GFDL CC-BY-SA-3.0], via Wikimedia Commons (a) Calcium hydroxide has the fmula Ca(OH) 2 Why are there two hydroxide ions f each calcium ion in the fmula? () Page 3 of 28

4 (b) The calcium hydroxide is used in the fm of nanoparticles. What are nanoparticles? () (c) A student added water to calcium oxide to make calcium hydroxide. The equation f the reaction is shown below. CaO + H 2 O Ca(OH) 2 Calculate the maximum mass of calcium hydroxide which could be made from 2.00 g of calcium oxide. Relative atomic masses (A r ): H = ; O = 6; Ca = 40. Maximum mass of calcium hydroxide =... g (3) (Total 5 marks) 3 Aspirin tablets have imptant medical uses. Page 4 of 28

5 A student carried out an experiment to make aspirin. The method is given below.. Weigh 2.00 g of salicylic acid. 2. Add 4 cm 3 of ethanoic anhydride (an excess). 3. Add 5 drops of concentrated sulfuric acid. 4. Warm the mixture f 5 minutes. 5. Add ice cold water to remove the excess ethanoic anhydride. 6. Cool the mixture until a precipitate of aspirin is fmed. 7. Collect the precipitate and wash it with cold water. 8. The precipitate of aspirin is dried and weighed. (a) The equation f this reaction is shown below. C 7 H 6 O 3 + C 4 H 6 O 3 C 9 H 8 O 4 + CH 3 COOH salicylic acid aspirin Calculate the maximum mass of aspirin that could be made from 2.00 g of salicylic acid. The relative fmula mass (M r ) of salicylic acid, C 7 H 6 O 3, is 38 The relative fmula mass (M r ) of aspirin, C 9 H 8 O 4, is Maximum mass of aspirin =... g (2) (b) The student made.0 g of aspirin from 2.00 g of salicylic acid. Calculate the percentage yield of aspirin f this experiment. (If you did not answer part (a), assume that the maximum mass of aspirin that can be made from 2.00 g of salicylic acid is 2.50 g. This is not the crect answer to part (a).) Percentage yield of aspirin =... % (2) Page 5 of 28

6 (c) Suggest one possible reason why this method does not give the maximum amount of aspirin () (d) Concentrated sulfuric acid is a catalyst in this reaction. Suggest how the use of a catalyst might reduce costs in the industrial production of aspirin () (Total 6 marks) 4 A student investigated the reactions of copper carbonate and copper oxide with dilute hydrochlic acid. In both reactions one of the products is copper chlide. (a) Describe how a sample of copper chlide crystals could be made from copper carbonate and dilute hydrochlic acid. (4) Page 6 of 28

7 (b) A student wanted to make.0 g of copper chlide. The equation f the reaction is: CuCO 3 + 2HCl CuCl 2 + H 2 O + CO 2 Relative atomic masses, A r : H = ; C = 2; O = 6; Cl = 35.5; Cu = 63.5 Calculate the mass of copper carbonate the student should react with dilute hydrochlic acid to make.0 g of copper chlide. Mass of copper carbonate =... g (4) (c) The percentage yield of copper chlide was 79. %. Calculate the mass of copper chlide the student actually produced. Actual mass of copper chlide produced =... g (2) Page 7 of 28

8 (d) Look at the equations f the two reactions: Reaction Reaction 2 CuCO 3 (s) + 2HCl(aq) CuCl 2 (aq) + H 2 O(l) + CO 2 (g) CuO(s) + 2HCl(aq) CuCl 2 (aq) + H 2 O(l) Reactive fmula masses: CuO = 79.5; HCl = 36.5; CuCl 2 = 34.5; H 2 O = 8 The percentage atom economy f a reaction is calculated using: Calculate the percentage atom economy f Reaction 2. Percentage atom economy =... % (3) (e) The atom economy f Reaction is %. Compare the atom economies of the two reactions f making copper chlide. Give a reason f the difference. () (Total 4 marks) Page 8 of 28

... Cl 2 +... e () 5 This question is about zinc and magnesium. Zinc is produced by electrolysis of molten zinc chlide, as shown in the figure below.

9 ... Cl e () 5 This question is about zinc and magnesium. Zinc is produced by electrolysis of molten zinc chlide, as shown in the figure below. (a) (i) Why must the zinc chlide be molten f electrolysis? () (ii) Describe what happens at the negative electrode. (3) (iii) Complete the half equation f the reaction at the positive electrode. (b) Magnesium can be produced from magnesium oxide. The equation f the reaction is: Si(s) + 2 MgO(s) SiO 2 (s) + 2 Mg(g) (i) How can you tell from the equation that the reaction is done at a high temperature? () Page 9 of 28

10 (ii) This reaction to produce magnesium from magnesium oxide is endothermic. What is meant by an endothermic reaction? () (iii) A company made magnesium using this reaction. Calculate the mass of magnesium oxide needed to produce.2 tonnes of magnesium. Relative atomic masses (A r ): O = 6; Mg = 24 Mass of magnesium oxide needed =... tonnes (3) (iv) The company calculated that they would produce.2 tonnes of magnesium, but only 0.9 tonnes was produced. Calculate the percentage yield. Percentage yield =... % () (v) Give one reason why the calculated yield of magnesium might not be obtained. () (Total 2 marks) Page 0 of 28

11 6 Sodium hydroxide neutralises sulfuric acid. The equation f the reaction is: 2NaOH + H 2 SO 4 Na 2 SO 4 + 2H 2 O (a) Sulfuric acid is a strong acid. What is meant by a strong acid? (2) (b) Write the ionic equation f this neutralisation reaction. Include state symbols. (2) (c) A student used a pipette to add 25.0 cm 3 of sodium hydroxide of unknown concentration to a conical flask. The student carried out a titration to find out the volume of 0.00 mol / dm 3 sulfuric acid needed to neutralise the sodium hydroxide. Describe how the student would complete the titration. You should name a suitable indicat and give the colour change that would be seen. (4) Page of 28

12 Mean volume =... cm 3 (2) Concentration =... mol / dm 3 (4) (d) The student carried out five titrations. Her results are shown in the table below. Titration Titration 2 Titration 3 Titration 4 Titration 5 Volume of 0.00 mol / dm sulfuric acid in cm 3 Concdant results are within 0.0 cm 3 of each other. Use the student s concdant results to wk out the mean volume of 0.00 mol / dm 3 sulfuric acid added. (e) The equation f the reaction is: 2NaOH + H 2 SO 4 Na 2 SO 4 + 2H 2 O Calculate the concentration of the sodium hydroxide. Give your answer to three significant figures. Page 2 of 28

13 (f) The student did another experiment using 20 cm 3 of sodium hydroxide solution with a concentration of 0.8 mol / dm 3. Relative fmula mass (M r ) of NaOH = 40 Calculate the mass of sodium hydroxide in 20 cm 3 of this solution. Mass =... g (2) (Total 6 marks) 7 A student investigated the rate of reaction of magnesium and hydrochlic acid. Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g) The student studied the effect of changing the concentration of the hydrochlic acid. She measured the time f the magnesium to stop reacting. Concentration of hydrochlic acid in moles per dm (a) The student changed the concentration of the hydrochlic acid. Give two variables that the student should control (2) Page 3 of 28

14 (b) (i) The rate of reaction increased as the concentration of hydrochlic acid increased. Explain why. (2) (ii) Explain why increasing the temperature would increase the rate of reaction. (3) Page 4 of 28

15 (c) (i) The student had a solution of sodium hydroxide with a concentration of 0.00 moles per dm 3. She wanted to check the concentration of a solution of hydrochlic acid. She used a pipette to transfer 5.00 cm 3 of the hydrochlic acid into a conical flask. She filled a burette with the 0.00 moles per dm 3 sodium hydroxide solution. Describe how she should use titration to obtain accurate results. (4) Page 5 of 28

16 (ii) Sodium hydroxide neutralises hydrochlic acid as shown in the equation: NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l) The student found that cm 3 of 0.00 moles per dm 3 sodium hydroxide neutralised 5.00 cm 3 of hydrochlic acid. Calculate the concentration of the hydrochlic acid in moles per dm 3. Give your answer to three significant figures. Concentration of hydrochlic acid =... moles per dm 3 (3) (Total 4 marks) Page 6 of 28

8 Air bags are used to protect the passengers in a car during an accident. When the crash sens detects an impact it causes a mixture of chemicals to be heated to a high temperature.

17 8 Air bags are used to protect the passengers in a car during an accident. When the crash sens detects an impact it causes a mixture of chemicals to be heated to a high temperature. Reactions take place which produce nitrogen gas. The nitrogen fills the air bag. (a) The mixture of chemicals contains sodium azide (NaN 3 ) which decomposes on heating to fm sodium and nitrogen. 2NaN 3 2Na + 3N 2 A typical air bag contains 30 g of sodium azide. (i) Calculate the mass of nitrogen that would be produced when 30 g of sodium azide decomposes. Relative atomic masses (A r ): N = 4; Na = 23 Mass of nitrogen =... g (3) (ii) g of nitrogen has a volume of 0.86 litres at room temperature and pressure. What volume of nitrogen would be produced from 30 g of sodium azide? (If you did not answer part (a)(i), assume that the mass of nitrogen produced from 30 g of sodium azide is 80 g. This is not the crect answer to part (a)(i).) Volume =... litres () Page 7 of 28

18 (b) The sodium produced when the sodium azide decomposes is dangerous. The mixture of chemicals contains potassium nitrate and silicon dioxide which help to make the sodium safe. (i) Sodium reacts with potassium nitrate to make sodium oxide, potassium oxide and nitrogen. Complete the balancing of the equation f this reaction. 0Na +...KNO 3 Na 2 O + K 2 O + N 2 () (ii) The silicon dioxide reacts with the sodium oxide and potassium oxide to fm silicates. Suggest why sodium oxide and potassium oxide are dangerous in contact with the skin. () (Total 6 marks) Page 8 of 28

19 Mark schemes (a) copper has delocalised electrons accept copper has free electrons igne sea of electrons mobile electrons (electrons) which can move through the metal / structure (b) (i) (M r FeCl 3 =) 62.5 allow (electrons) which can carry a charge through the metal / structure crect answer with without wking gains 3 marks can be credited from crect substitution in step 2 2 (moles of) FeCl 3 = allow ecf from step accept = 32.5 accept (ii) 74.8 accept accept ecf from (b)(i) if there is no answer to part(i) if candidate chooses not to use their answer then accept [6] Page 9 of 28

20 2 (a) because calcium is +2 and hydroxide is accept to balance the charges to make the compound neutral (in terms of charges) allow calcium needs to lose 2 electrons and hydroxide needs to gain one electron (b) particles of size -00 nm allow clear comparison to nmal size particles particles with a few hundred atoms / ions particles with a high surface area (to volume ratio) as different properties to nmal size particles of the same substance (c) M r CaO = 56 and M r Ca(OH) 2 = 74 2/56 (x74) (x74) allow ecf from step 74/56 (x2).3(24 ) (x2) 2.6(428 ) in range 2.6 to 2.96 crect answer with without wking gains 3 marks allow ecf carried through from step igne final rounding to 3 [5] Page 20 of 28

21 3 (a) 2.6 / range 2.5 to 2.7 (b) 42. range 40.7 to 42.3 crect answer with without with wrong wking gains 2 marks (accept answers between 2.5 and 2.7) if answer increct moles of salicylic acid = 2/38 = moles ie 2/ gains mark (80/38) 2 gains mark g 80/38 = (.304 g) gains mark (not.304g alone) accept crect answer with without with wrong wking f 2 marks ecf ie (. / their answer from (a)) 00 crectly calculated gains 2 marks if answer increct percentage yield =. / gains mark if they do not have an answer to part (a) they choose not to use their answer then: yield = (. / 2.5) 00 () 2 = 44 accept 44 f 2 marks with no wking 2 (c) any one from: errs in weighing some (of the aspirin) lost do not allow lost as a gas not all of the reactant may have been converted to product eg reaction didn t go to completion allow loss of some reactants the reaction is reversible accept other products / chemicals side reactions igne waste products reactants impure not heated f long enough not hot enough f reaction to take place Page 2 of 28

22 (d) any one from: use lower temperature use less fuel / energy igne references to use of catalyst produce product faster speed up reaction me product produced in a given time (owtte) increased productivity lowers activation energy [6] 4 (a) add excess copper carbonate (to dilute hydrochlic acid) accept alternatives to excess, such as until no me reacts filter (to remove excess copper carbonate) reject heat until dry heat filtrate to evapate some water heat to point of crystallisation accept leave to evapate leave in evapating basin leave to cool (so crystals fm) until crystals fm must be in crect der to gain 4 marks (b) M r CuCl 2 = 34.5 crect answer sces 4 marks moles copper chlide = (mass / M r = / 34.5) = M r CuCO 3 = 23.5 Mass CuCO 3 (=moles M 2 = ) = 0.(00) Page 22 of 28

23 accept 0. with no wking shown f 4 marks (c) (g) accept 8.70(g) with no wking shown f 2 marks (d) Total mass of reactants = (%) allow ecf from step allow with no wking shown f 3 marks (e) atom economy using carbonate lower because an additional product is made carbon dioxide is made as well allow ecf [4] Page 23 of 28

24 5 (a) (i) so ions can move (and carry charge) accept so current can flow allow so it can conduct (electricity) allow so charged particles can move do not accept so electrons can move (ii) because zinc ions gain electrons accept because zinc ions are reduced 2 (electrons) zinc is fmed accept crect half equation f 3 marks if no mark gained allow positive ions go to negative electrode opposites attract reduction (of zinc) (zinc) gains electrons f mark (iii) 2 Cl Cl e must be completely crect (b) (i) because the magnesium is a gas allow magnesium goes from solid to gas (ii) (a reaction which) takes in energy (from the surroundings) accept me energy needed to break bonds than released by fming bonds accept crect reference to energy level diagram allow (a reaction which) takes in heat (from the surroundings) (iii) (M r MgO =) 40 accept (2 M r MgO =) 80.2 / 24 (x40) 0.05 (x40) 40 / 24 (x.2).67 (x.2) allow ecf from step 2(.0) Page 24 of 28

25 (iv) 75(%) allow ecf carried through from step crect answer with without wking gains 3 marks (v) any one from: the reaction is reversible accept incomplete reaction igne equilibrium not reached some lost / escaped / released (when separated) some of the reactant may react in different ways from the expected reaction impure reactant(s) igne measurement and calculation errs [2] 6 (a) (sulfuric acid is) completely / fully ionised (b) (c) In aqueous solution when dissolved in water H + (aq) + OH (aq) H 2 O(l) allow multiples mark f equation mark f state symbols adds indicat, eg phenolpthalein / methyl ange / litmus added to the sodium hydroxide (in the conical flask) do not accept universal indicat (adds the acid from a) burette with swirling dropwise towards the end point until the indicat just changes colour until the indicat changes from pink to colourless (f phenolphthalein) yellow to red (f methyl ange) blue to red (f litmus) 2 (d) titrations 3, 4 and 5 Page 25 of 28

26 27.2 cm 3 accept 27.2 with no wking shown f 2 marks allow with no wking shown f 2 marks (e) Moles H 2 SO 4 = conc vol = allow ecf from 8.4 Ratio H 2 SO 4 :NaOH is :2 Moles NaOH = Moles H 2 SO 4 2 = Concentration NaOH = mol / vol = / = (mol / dm 3 ) accept 0.27 with no wking f 4 marks accept with no wking f 3 marks (f) 0.8 = no of moles g 0.44 (g) accept 0.44g with no wking f 2 marks [6] 7 (a) any two from: temperature (of the HCl) mass length of the magnesium surface area of the magnesium volume of HCl (b) (i) (a greater concentration has) me particles per unit volume allow particles are closer together therefe me collisions per unit time me frequent collisions. 2 (ii) particles move faster allow particles have me (kinetic) energy Page 26 of 28

27 therefe me collisions per unit time me frequent collisions collisions me energetic (therefe me collisions have energy greater than the activation energy) me productive collisions (c) (i) add (a few drops) of indicat to the acid in the conical flask allow any named indicat add NaOH (from the burette) until the indicat changes colour add the NaOH dropwise candidate does not have to state a colour change but penalise an increct colour change. repeat the titration calculate the average volume of NaOH repeat until concdant results are obtained (ii) moles of NaOH = moles crect answer with without wking gains 3 marks Concentration of HCl / = allow ecf from mp to mp2 crect number of significant figures [4] Page 27 of 28

28 8 (a) (i) 84 / 84.5 / crect answer with without wking gains 3 marks (moles of NaN 3 =) 30/65 () moles of nitrogen = 3 () mass of nitrogen = 3 x 28 = 84 () 2 x (23 + (3 x 4)) () 3 x (2 x4) () 2NaN 3 = 30 () 3N 2 = 84 () (ii) 72 / / 72.2 if answer is increct then look f evidence of crect wking. allow ecf from previous stage mark lost f each mistake in the wking if they do not have the crect answer. allow ecf from part (i) igne wking (b) (i) 2 and 5 (ii) any one from: crosive / burns alkaline / basic do not accept acidic attacks / destroys / damages living tissue / cells allow irritant igne reference to reactivity igne reference to silicates igne harmful / toxic [6] Page 28 of 28

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