Past Questions on Reacting Quantities
Q1 Lithium burns in air to produce Lithium oxide (Li2O). Write a balanced equation for this
reaction.
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[2]
In an experiment, a student burnt 0.78g of lithium. Calculate the mass of lithium oxide that would be
produced. Give your answer to 2 significant figures.
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[3]
[Total 5 marks]
Q2 Tetrachloromethane CCl4 is manufactured by reacting methane, CH4 with an excess of chlorine
according to the unbalanced equation:
…….CH4(g) + …….Cl2(g)  …….CCl4(l) + …….HCl(g)
(i) balance the equation above.
[1]
(ii) Calculate the mass of methane required to produce 5kg of CCl4. Give your answer to 2 significant
figures
[3]
(iii) Calculate the volume in dm3 measured at room temperature and pressure of Cl2 required to
produce 5kg of CCl4. Give your answer to 2 significant figures
[2]
Q3 A student had a stomach-ache and needed to take something to neutralise excess stomach
acid. He decided to take some Milk of Magnesia, which is an aqueous suspension of
magnesium hydroxide, Mg(OH)2.
(a)
The main acid in the stomach is hydrochloric acid, HCl(aq), and the unbalanced
equation for the reaction that takes place with Milk of Magnesia is shown below.
….....Mg(OH)2(s) + ….....HCl(aq)  ….....MgCl2(aq) + ….....H2O(l)
Balance the equation by adding numbers where necessary in the unbalanced
equation above.
[1]
(b)
The student’s stomach contained 500 cm3 of stomach fluid with an acid
concentration of 0.108 mol dm–3. The student swallowed some Milk of Magnesia
containing 2.42 g Mg(OH)2. He wondered whether this dose was sufficient to
neutralise the stomach acid.
Assume that all the acid in the stomach fluid was 0.108 mol dm–3 hydrochloric
acid.
(i)
How many moles of HCl were in the 500 cm3 of stomach fluid?
[1]
(ii)
Calculate the mass of Mg(OH)2 necessary to neutralise this stomach fluid.
[3]
(iii)
Determine whether the student swallowed too much, too little, or just the
right amount of Milk of Magnesia to neutralise the stomach acid.
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[1]
[Total 6 marks]
Q4 A student heats 5.29 g of Sr(NO3)2 and collects the gas at room temperature and pressure, RTP.
The equation for the reaction is given below.
2Sr(NO3)2(s) → 2SrO(s) + 4NO2(g) + O2(g)
Calculate the volume of gas, in cm3, obtained by the student at RTP.
[Total 4 marks]
Q5 Calcium and its compounds, have properties typical of Group 2 in the Periodic Table.
Calcium carbonate, CaCO3, reacts with acids such as nitric acid.
A student neutralised 2.68 g of CaCO3 with 2.50 mol dm–3 nitric acid, HNO3.
The equation for this reaction is shown below.
CaCO3(s) + 2HNO3(aq) → Ca(NO3)2(aq) + CO2(g) + H2O(l)
(i)
Determine the amount, in mol, of CaCO3 reacted.
amount = ............................................... mol
[2]
(ii)
Calculate the volume, in cm3, of CO2 produced at room temperature and
pressure.
volume = ...............................................cm3
[1]
(iii)
Calculate the volume of 2.50 mol dm–3 HNO3 needed to neutralise 2.68 g of
CaCO3.
volume = ............................................... cm3
[2]
[Total 5 marks]
Q6 (a) A student carries out a titration to find the concentration of some sulfuric acid.
The student finds that 25.00 cm3 of 0.0880 mol dm–3 aqueous sodium
hydroxide, NaOH, is neutralised by 17.60 cm3 of dilute sulfuric acid, H2SO4.
H2SO4(aq) + 2NaOH(aq) → Na2SO4(aq) + 2H2O(l)
(i)
Calculate the amount, in moles, of NaOH used.
answer = ................................... mol
[1]
(ii)
Determine the amount, in moles, of H2SO4 used.
answer = ................................... mol
[1]
(iii)
Calculate the concentration, in mol dm–3, of the sulfuric acid.
answer = ................................... mol dm–3
[1]
Q7 Calcium carbonate, CaCO3, reacts with hydrochloric acid as shown in the equation below.
CaCO3(s) + 2HCl (aq) → CaCl2(aq) + H2O(l) + CO2(g)
7.50 × 10–3 mol CaCO3 reacts with 0.200 mol dm–3 HCl.
(i)
Calculate the volume, in cm3, of 0.200 mol dm–3 HCl required to react
with 7.50 × 10–3 mol CaCO3.
answer = ................................................. cm3
[2]
(ii)
Calculate the volume, in cm3, of CO2 formed at room temperature and pressure.
answer = ................................................. cm3
[1]
[Total 3 marks]
Q8 The Group 2 element barium, Ba, is silvery white when pure but blackens when exposed to air.
The blackening is due to the formation of both barium oxide and barium nitride. The nitride ion is
N3–.
(a) Predict the formula of:
barium oxide ………………………… barium nitride ………………………… [2]
(b) A 0.11 g sample of pure barium was added to 100 cm3 of water.
Ba(s) + 2H2O(l)  Ba(OH)2(aq) + H2(g)
(i) Show that 8.0 × 10−4 mol of Ba were added to the water. [1]
(ii) Calculate the volume of hydrogen, in cm3, produced at room temperature and pressure.
volume = ................................................. cm3 [1]
(iii) Calculate the concentration, in mol dm−3, of the Ba(OH)2(aq) solution formed.
concentration = ......................................... mol dm−3 [1]
(iv) State the approximate pH of the Ba(OH)2(aq) solution.
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(c) A student repeated the experiment in (b) using a 0.11 g sample of barium that had blackened
following exposure to the air. Suggest why the volume of hydrogen produced would be slightly less
than the volume collected using pure barium
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Q9 Dilute sulfuric acid reacts with alkalis such as sodium hydroxide.
Solid sodium hydroxide is known as caustic soda. It has a household use as a drain cleaner.
A student believes a box of caustic soda has been accidentally contaminated.
• To prove this, the student dissolves 2.00 g of the impure caustic soda in water and the solution is
made up to 250 cm3.
• 25.0 cm3 of this solution of caustic soda is neutralised by 24.60 cm3 of 0.100 mol dm–3 dilute
sulfuric acid.
H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l)
(i)
Calculate the amount, in moles, of H2SO4 used.
answer = .................................. mol [1]
(ii)
Determine the amount, in moles, of NaOH in the 25.0 cm3 used.
answer = .................................. mol [1]
(iii)
Calculate the percentage, by mass, of NaOH in the impure caustic soda.
answer = .................................. [3]
Q10 A student carried out an experiment to find out the volume of carbon dioxide obtained by
heating a weighed sample of magnesium carbonate.
The student placed a 1.47 g sample of MgCO3 into a test-tube and heated it until there was no
further change in mass. The following reaction took place.
MgCO3(s)  MgO(s) + CO2(g)
What volume of CO2, in dm3, would have been given off when measured at room temperature and
pressure?
The molar mass of MgCO3 = 84.3 g mol–1
answer = ..................................dm3 [2]
Q11 Sodium tartrate and copper(II) nitrate are both salts.
(a) Sodium tartrate is a salt of tartaric acid. The formula of tartaric acid can be represented as HxA.
In this formula, x is the number of H+ ions that can be replaced by metal ions to form salts.
A student carries out a titration to find the value of x in the formula of tartaric acid, HxA.
In the titration, 25.00 cm3 of 0.0500 mol dm–3 tartaric acid, HxA, exactly reacts with 12.50 cm3 of
0.200 mol dm–3 sodium hydroxide, NaOH. A solution of sodium tartrate is produced.
(i) Calculate the amount, in mol, of HxA used.
amount = ................................................. mol [1]
(ii) Calculate the amount, in mol, of NaOH used.
amount = ................................................. mol [1]
(iii) Deduce the value for x in the formula of tartaric acid, HxA.
x = ........................................................ [1]
Q12 Calcium hydroxide is used in agriculture but the amounts used must be carefully controlled.
(a) State one use of calcium hydroxide in agriculture and suggest why the amount of calcium
hydroxide used should not be excessive.
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(b) A student knew that calcium hydroxide could be made by adding calcium to water.
The student added 0.00131 mol of calcium to a beaker containing about 100 cm3 of water.
A reaction took place as shown by the equation below. All the calcium hydroxide formed was
soluble.
Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g)
(i) Calculate the mass of calcium that the student added.
mass of calcium = ..................................................... g [1]
(ii) Calculate the volume of hydrogen gas, in dm3, produced in this reaction at room temperature
and pressure, RTP.
volume of hydrogen gas = ................................................. dm3 [1]
(iii) The student transferred the contents of the beaker to a 250 cm3 volumetric flask and water was
added to make the solution up to 250 cm3.
Calculate the concentration, in mol dm–3, of hydroxide ions in the 250 cm3 solution.
concentration = ......................................... mol dm–3 [2]
(c) The student repeated the experiment using the same mass of pure barium.
The student found that a smaller volume of hydrogen gas was produced, measured at RTP.
(i) Explain why.
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Q13 Pharmacists sell tablets containing magnesium hydroxide, Mg(OH)2, to combat indigestion. A
student carried out an investigation to find the percentage by mass of Mg(OH)2 in an indigestion
tablet. The student reacted the tablet with dilute hydrochloric acid.
Mg(OH)2(s) + 2HCl(aq)  MgCl2(aq) + 2H2O(l)
The student found that 32.00 cm3 of 0.500 mol dm–3 HCl was needed to react with the Mg(OH)2 in a
500 mg tablet. [1 g = 1000 mg].
(i) Calculate the amount, in mol, of HCl used.
amount = ................................................. mol [1]
(ii) Determine the amount, in mol, of Mg(OH)2 present in the tablet.
amount = ................................................. mol [1]
(iii) Determine the percentage by mass of Mg(OH)2 present in the tablet.
answer = .................................................... % [3]
Q14 Potassium metal reacts with water according to the equation.
2K(s) + 2H2O(l)  2KOH(aq) + H2(g)
0.2346 g of potassium is reacted with excess water.
Calculate the volume of gas formed.
The gas volume is measured in cm3 at room temperature and pressure.
answer = .................................................. cm3 [3]