Quantitative ChemistryAQA GCSE Chemistry: Topic test

20 questions, 54 marks

AQA GCSE Chemistry

Quantitative Chemistry topic test

Total 54 marks

Name

Class

Date

1
An analytical chemist working for a vitamin supplement company checks a batch of tablets containing ascorbic acid (vitamin C, C6H8O6), each labelled as containing 0.50 g of the vitamin, before the tablets are approved for sale.
(a)
What is the relative formula mass (Mr) of ascorbic acid, C6H8O6? (Ar: C = 12, H = 1, O = 16)
[1 mark]
A176
B168
C80
D29
(b)
How many moles of ascorbic acid are there in a tablet containing 0.50 g, given Mr = 176?
[1 mark]
A0.50 / 12 = 0.0417 mol
B0.50 / 176 = 0.00284 mol
C176 / 0.50 = 352 mol
D0.50 x 176 = 88 mol
(c)
The label claims each tablet contains 0.50 g of ascorbic acid. Calculate the number of moles of ascorbic acid this represents, giving your answer to 3 significant figures. (Mr = 176)
[2 marks]
Total for question 1: 4 marks
2
A firework manufacturer burns a small, carefully measured sample of aluminium powder inside a sealed calorimeter filled with oxygen gas, to confirm the balanced equation for the formation of aluminium oxide and check that their firework formulations use accurate reactant ratios.
(a)
What does the law of conservation of mass state about a chemical reaction such as this one?
[1 mark]
AThe mass of the products is always less than the mass of the reactants
BThe mass of the products is always greater than the mass of the reactants
CThe total mass of the reactants equals the total mass of the products, because no atoms are lost or made
DMass can be lost as heat energy during an exothermic reaction
(b)
The balanced symbol equation for this reaction is 4Al + 3O2 -> 2Al2O3. What does the number 3 in front of O2 represent?
[1 mark]
AThe number of oxygen atoms in one molecule of oxygen
BThe relative formula mass of oxygen
CThe charge on the oxide ion
DThe number of oxygen molecules needed to balance the equation
(c)
Explain why the manufacturer burns the aluminium inside a sealed calorimeter rather than in an open container, in terms of demonstrating the law of conservation of mass.
[2 marks]
Total for question 2: 4 marks
3
A chemical supplier makes copper sulfate crystals for school laboratories by reacting copper oxide with dilute sulfuric acid, then evaporating and crystallising the solution. The company checks the percentage yield and atom economy of the process as part of a sustainability audit.
(a)
The reaction is CuO + H2SO4 -> CuSO4 + H2O (Mr: CuO = 80, H2SO4 = 98, CuSO4 = 160). Calculate the atom economy for the production of copper sulfate in this reaction, giving your answer to 3 significant figures.
[3 marks]
(b)
In one batch, 8.0 g of copper oxide (Mr = 80) reacts with excess sulfuric acid. Calculate the maximum theoretical mass of copper sulfate (Mr = 160) that could be produced, then calculate the percentage yield if only 13.5 g of copper sulfate crystals are actually collected.
[4 marks]
Total for question 3: 7 marks
4
An environmental laboratory analyses a factory's waste discharge. Technicians react a measured volume of the waste solution, which contains a known concentration of dissolved carbonate ions, with an excess of dilute hydrochloric acid, and collect and measure the volume of carbon dioxide gas produced at room temperature and pressure to check compliance with a discharge permit that limits both the concentration of dissolved carbonate and the volume of gas that can be released.
(a)
A 250 cm3 sample of the waste discharge is found to contain 2.65 g of dissolved sodium carbonate (Na2CO3, Mr = 106). Calculate the concentration of the discharge in g/dm3 and in mol/dm3, and explain whether the measured concentration in mol/dm3 would double, stay the same, or halve if the laboratory instead analysed 500 cm3 of the same waste discharge.
[6 marks]
(b)
When excess dilute hydrochloric acid is added to a 100 cm3 sample of the discharge containing 0.040 mol of dissolved sodium carbonate, carbon dioxide gas is produced according to the equation: Na2CO3 + 2HCl -> 2NaCl + H2O + CO2. Calculate the volume of carbon dioxide gas produced at room temperature and pressure, and explain what would happen to this volume if the hydrochloric acid, rather than the sodium carbonate, were the limiting reactant instead.
[6 marks]
Total for question 4: 12 marks
5
A lime works heats calcium carbonate in a large kiln to produce calcium oxide (quicklime) for the construction industry, releasing carbon dioxide gas as a by-product. Technicians note that the total mass of solid material decreases significantly after heating.
(a)
Which type of reaction is occurring when calcium carbonate breaks down on heating to form calcium oxide and carbon dioxide?
[1 mark]
AThermal decomposition
BNeutralisation
CDisplacement
DCombustion
(b)
The technicians find that the mass of solid remaining after heating is less than the starting mass of calcium carbonate, even though no atoms are lost in the reaction. Which statement correctly explains this observation?
[1 mark]
AMass is not conserved in this reaction
BCarbon dioxide gas escapes into the air, so it is not included in the mass of solid remaining, even though the total mass of all products equals the mass of reactants
CSome calcium atoms are destroyed during the reaction
DThe calcium oxide produced weighs less than an equal number of calcium atoms
(c)
If this thermal decomposition reaction were instead carried out in a sealed container, and the whole container (including the carbon dioxide gas produced) were weighed before and after heating, explain what the technicians would find, and why.
[2 marks]
Total for question 5: 4 marks
6
A steelworks tests a delivery of haematite ore (Fe2O3, Mr = 160) to calculate the percentage by mass of iron it contains, to estimate how much usable iron the ore will yield before purchasing a large shipment.
(a)
What is the relative formula mass of iron(III) oxide, Fe2O3? (Ar: Fe = 56, O = 16)
[1 mark]
A104
B144
C160
D72
(b)
The steelworks calculates that the percentage by mass of iron in Fe2O3 is 70%. Which calculation correctly shows this?
[1 mark]
A56 / 160 x 100
B48 / 160 x 100
C160 / 112 x 100
D112 / 160 x 100
(c)
A shipment contains 500 tonnes of pure haematite ore. Calculate the maximum mass of iron, in tonnes, that the ore could theoretically yield.
[2 marks]
Total for question 6: 4 marks
7
A toothpaste manufacturer precipitates calcium carbonate from calcium chloride and sodium carbonate solutions to use as a mild abrasive, and needs to calculate the atom economy and percentage yield of this precipitation reaction for a batch production report.
(a)
The reaction is CaCl2 + Na2CO3 -> CaCO3 + 2NaCl (Mr: CaCl2 = 111, Na2CO3 = 106, CaCO3 = 100). Calculate the atom economy for the production of calcium carbonate in this reaction, giving your answer to 3 significant figures.
[3 marks]
(b)
22.2 g of calcium chloride (Mr = 111) reacts with excess sodium carbonate solution. The theoretical maximum mass of calcium carbonate (Mr = 100) that could form is 20.0 g, but the manufacturer actually collects 17.4 g of dry calcium carbonate. Calculate the percentage yield, and suggest one reason why the yield is less than 100%.
[4 marks]
Total for question 7: 7 marks
8
A school science department repeats a classic reaction between magnesium and oxygen to help students practise mole calculations. One group of students reacts magnesium with oxygen and uses the mass data to work out the balanced equation, while a second group's results at first appear to break the law of conservation of mass.
(a)
A group of students reacts 3.0 g of magnesium completely with oxygen gas and measures that 5.0 g of magnesium oxide is formed. Calculate the number of moles of magnesium and the number of moles of oxygen gas (O2) that reacted, and use these to deduce the simplest whole-number mole ratio and the balanced symbol equation for the reaction. (Ar: Mg = 24, O = 16)
[6 marks]
(b)
A second group of students burns magnesium in an open crucible and finds that the total mass of the solid after heating is greater than the starting mass of magnesium, apparently gaining mass from nowhere. Explain why this result does not break the law of conservation of mass, and describe how the experiment could be adapted to directly demonstrate that mass is conserved.
[6 marks]
Total for question 8: 12 marks

End of questions