R2.1 How much? The amount of chemical change
Practice exam-style IB Chemistry questions for How much? The amount of chemical change, aligned with the syllabus and grouped by topic.
Question 1
The equation for the formation of ammonia is shown.
[\ce{N2
A.
1 : 2
B.
3 : 1
C.
3 : 2
D.
2 : 3
Question 2
What is the sum of the coefficients when the equation is balanced using the smallest whole numbers?
[\ce{__Al
A.
8
B.
5
C.
4
D.
7
Question 3
Magnesium reacts with hydrochloric acid.
[\ce{Mg
A.
0.250
B.
0.125
C.
0.500
D.
1.00
Question 4
The theoretical yield of a salt is 12.0 g. The experimental yield is 9.60 g.
A.
20.0%
B.
80.0%
C.
125%
D.
96.0%
Question 5
Aqueous sodium carbonate reacts with hydrochloric acid to form aqueous sodium chloride, carbon dioxide and water.
Write the balanced chemical equation, including state symbols.
[1]
State the mole ratio of sodium carbonate to hydrochloric acid.
[1]
Question 6
Distinguish between theoretical yield and experimental yield.
[1]
Suggest one reason why the experimental yield of a precipitate may be lower than the theoretical yield.
[1]
Question 7
A reaction has a theoretical yield of 4.25 g. A student obtains 3.74 g of product.
Calculate the percentage yield.
[1]
State why the same unit must be used for experimental and theoretical yield in this calculation.
[1]
Question 8
What mass of (\ce{CO2}), in g, is produced by complete combustion of 0.200 mol of methane?
[\ce{CH4
A.
17.6
B.
8.80
C.
22.0
D.
4.40
Question 9
0.300 mol of hydrogen is mixed with 0.200 mol of oxygen.
[\ce{2H2
A.
\(\ce{O2}\); 0.200 mol
B.
\(\ce{H2}\); 0.150 mol
C.
\(\ce{O2}\); 0.400 mol
D.
\(\ce{H2}\); 0.300 mol
Question 10
Ethene reacts with hydrogen to form ethane.
[\ce{C2H4
A.
87%
B.
cannot be determined without the experimental yield
C.
50%
D.
100%
Question 11
When propan-1-ol undergoes complete combustion, carbon dioxide and water are the only products.
[\ce{C3H8O
A.
\(a=4.5,\ b=4,\ c=3\)
B.
\(a=4.5,\ b=3,\ c=4\)
C.
\(a=5.0,\ b=3,\ c=4\)
D.
\(a=6.0,\ b=3,\ c=8\)
Question 12
A student obtains a percentage yield of 108% for a dried precipitate.
A.
The limiting reactant was completely consumed.
B.
The precipitate contained water or impurities.
C.
The reaction went to completion.
D.
Some product was lost during filtration.
Question 13
Calcium carbonate decomposes on heating.
[\ce{CaCO3
-> CaO
[1]
- CO2(g)}]
A sample of 5.00 g of (\ce{CaCO3}) is completely decomposed.
[1]
Calculate the amount, in mol, of (\ce{CaCO3}). Use (M(\ce{CaCO3})=100.09, ext{g mol}^{-1}).
[1]
Determine the volume of (\ce{CO2}), in dm³, produced at STP. Use (V_m=22.7, ext{dm}^3, ext{mol}^{-1}).
[2]
Question 14
25.00 cm³ of sulfuric acid is neutralized by 18.60 cm³ of (0.120, ext{mol dm}^{-3}) potassium hydroxide.
[\ce{H2SO4(aq) + 2KOH(aq) -> K2SO4(aq) + 2H2O
(l)}]
[1]
Calculate the amount, in mol, of (\ce{KOH}) used.
[1]
Calculate the amount, in mol, of (\ce{H2SO4}) in the sample.
[1]
Determine the concentration of the sulfuric acid.
[1]
Question 15
Aluminium reacts with chlorine to form aluminium chloride.
[\ce{2Al
- 3Cl2
[1]
-> 2AlCl3(s)}]
0.500 mol of aluminium is mixed with 0.600 mol of chlorine.
[1]
Identify the limiting reactant.
[1]
Calculate the maximum amount, in mol, of (\ce{AlCl3}) formed.
[1]
Calculate the amount, in mol, of the excess reactant remaining.
[1]
Question 16
A student reacted magnesium ribbon with excess hydrochloric acid and collected hydrogen in a gas syringe.
[\ce{Mg
- 2HCl(aq) -> MgCl2(aq) + H2(g)}]
[1]
Use the graph to determine the final volume of hydrogen collected.
[1]
Calculate the amount of hydrogen collected at STP. Use (V_m=22.7, ext{dm}^3, ext{mol}^{-1}).
[1]
Determine the mass of magnesium that reacted. Use (M(\ce{Mg})=24.31, ext{g mol}^{-1}).
[1]
Question 17
A student prepared copper(II) hydroxide precipitate by mixing copper(II) sulfate and sodium hydroxide. The table shows the masses recorded during filtration and drying.
| Item | Mass / g |
|---|---|
| Filter paper | 1.82 |
| Filter paper + dry precipitate | 3.10 |
Determine the experimental yield of dry copper(II) hydroxide from the data.
[1]
The theoretical yield is 1.46 g. Calculate the percentage yield.
[1]
Suggest two reasons why the percentage yield may be below 100%.
[1]
Question 18
The graph shows the volumes of hydrogen and nitrogen used in mixtures for making ammonia.
[\ce{N2
- 3H2
[1]
-> 2NH3(g)}]
[1]
Use the graph to identify the mixture with the correct stoichiometric volume ratio.
[1]
For this mixture, determine the expected volume of ammonia if reaction is complete and all gases are at the same temperature and pressure.
[1]
State why volume ratios can be used for the reacting gases.
[1]
Question 19
25.0 cm³ of (0.200, ext{mol dm}^{-3}) sodium hydroxide reacts with sulfuric acid.
[\ce{H2SO4(aq) + 2NaOH(aq) -> Na2SO4(aq) + 2H2O
A.
\(1.00 imes10^{-2}\)
B.
\(5.00 imes10^{-3}\)
C.
\(2.50 imes10^{-3}\)
D.
\(2.50\)
Question 20
A gas syringe collects 45.4 cm³ of (\ce{H2}) at STP. Use (V_m=22.7, ext{dm}^3, ext{mol}^{-1}).
[\ce{Mg
A.
0.0486 g
B.
0.486 g
C.
2.00 g
D.
0.0243 g
Question 21
20.0 cm³ of (0.150, ext{mol dm}^{-3}) (\ce{BaCl2(aq)}) is mixed with excess (\ce{Na2SO4(aq)}).
[\ce{BaCl2(aq) + Na2SO4(aq) -> BaSO4
A.
7.00 g
B.
3.50 g
C.
0.350 g
D.
0.700 g
Question 22
8.00 g of (\ce{CuO}) reacts with 1.00 g of carbon.
[\ce{2CuO
A.
\(\ce{CuO}\), because it produces less copper
B.
\(\ce{C}\), because one mole reacts with two moles of \(\ce{CuO}\)
C.
\(\ce{CuO}\), because it has the larger mass
D.
\(\ce{C}\), because its mass is smaller
Question 23
Nitrobenzene can be prepared by nitration of benzene.
A.
100%
B.
87.2%
C.
46.3%
D.
115%
Question 24
A hydrocarbon burns completely. 10.0 cm³ of the hydrocarbon produces 40.0 cm³ of (\ce{CO2}), measured at the same temperature and pressure.
A.
2
B.
3
C.
5
D.
4
Question 25
What correctly distinguishes atom economy from percentage yield?
A.
Atom economy is measured in grams; percentage yield is measured in moles.
B.
Atom economy uses the balanced equation; percentage yield uses experimental and theoretical yields.
C.
Atom economy is always lower than percentage yield.
D.
Atom economy requires experimental yield; percentage yield requires only formula masses.
Question 26
Methanol can be made from carbon monoxide and hydrogen.
[\ce{CO
- 2H2
[1]
-> CH3OH(l)}]
[1]
Calculate the atom economy for methanol.
[1]
Explain why this value is favourable from a green chemistry perspective. [2]
Use (M(\ce{CO})=28.01), (M(\ce{H2})=2.02), (M(\ce{CH3OH})=32.05) in ( ext{g mol}^{-1}).
[1]
Question 27
Ammonia is produced by the Haber process.
[\ce{N2
- 3H2
[1]
-> 2NH3(g)}]
At the same temperature and pressure, 12.0 dm³ of nitrogen reacts completely with hydrogen.
[1]
Determine the volume of hydrogen required.
[1]
Determine the volume of ammonia produced.
[1]
Explain why gas volume ratios may be used in this calculation.
[2]
Question 28
Solid iron(III) oxide reacts with carbon monoxide to form solid iron and carbon dioxide.
Deduce the balanced equation, including state symbols.
[1]
State the mole ratio of carbon monoxide to iron produced.
[1]
State why coefficients, rather than subscripts, are changed when balancing equations.
[1]
Question 29
A 0.620 g sample of magnesium reacts with excess hydrochloric acid.
[\ce{Mg
- 2HCl(aq) -> MgCl2(aq) + H2(g)}]
[1]
Calculate the amount of magnesium. Use (M(\ce{Mg})=24.31, ext{g mol}^{-1}).
[1]
Calculate the volume of hydrogen, in cm³, produced at STP. Use (V_m=22.7, ext{dm}^3, ext{mol}^{-1}).
[1]
State one assumption made in the calculation.
[1]
Question 30
A student calculated a theoretical yield of 1.86 g for a hydrated salt. The mass recorded after drying was 1.97 g.
Calculate the percentage yield.
[1]
Explain why this result should be treated with caution.
[1]
Question 31
The table gives results for mixing different amounts of hydrochloric acid with a fixed amount of calcium carbonate.
[\ce{CaCO3
| HCl added / cm³ | CO₂ collected / cm³ |
|---|---|
| 5 | 12 |
| 10 | 24 |
| 15 | 36 |
| 20 | 48 |
| 25 | 60 |
| 30 | 60 |
| 35 | 60 |
- 2HCl(aq) -> CaCl2(aq) + CO2
[1]
- H2O(l)}]
[1]
Describe the trend in the volume of carbon dioxide as the volume of acid increases.
[1]
Use the data to identify when calcium carbonate first becomes the limiting reactant.
[1]
Explain why the carbon dioxide volume becomes constant at higher acid volumes.
[2]
Question 32
Two routes are proposed for producing ethyl ethanoate, (\ce{CH3COOCH2CH3}). The table gives equations and molar masses.
| Route | Balanced equation | Desired product | Molar masses / g mol⁻¹ |
|---|---|---|---|
| 1 | CH₃COOH + CH₃CH₂OH → CH₃COOCH₂CH₃ + H₂O | CH₃COOCH₂CH₃ | CH₃COOH 60.06; CH₃CH₂OH 46.08; CH₃COOCH₂CH₃ 88.10; H₂O 18.02 |
| 2 | (CH₃CO)₂O + CH₃CH₂OH → CH₃COOCH₂CH₃ + CH₃COOH | CH₃COOCH₂CH₃ | (CH₃CO)₂O 102.09; CH₃CH₂OH 46.08; CH₃COOCH₂CH₃ 88.10; CH₃COOH 60.06 |
Calculate the atom economy for ethyl ethanoate for route 1.
[1]
Calculate the atom economy for ethyl ethanoate for route 2.
[1]
Identify which route has the lower stoichiometric wastage.
[1]
State one limitation of using atom economy alone to select the greener route.
[1]
Question 33
A titration is carried out to determine the concentration of ethanedioic acid, (\ce{H2C2O4}), using sodium hydroxide.
[\ce{H2C2O4(aq) + 2NaOH(aq) -> Na2C2O4(aq) + 2H2O
| Trial | Initial reading / cm³ | Final reading / cm³ | Titre / cm³ |
|---|---|---|---|
| 1 | 0.15 | 24.80 | 24.65 |
| 2 | 1.20 | 25.90 | 24.70 |
| 3 | 0.05 | 24.70 | 24.65 |
(l)}]
The table gives three concordant titres of (0.100, ext{mol dm}^{-3}) (\ce{NaOH}) used to neutralize 25.00 cm³ of the acid.
[1]
Determine the mean titre from the concordant results.
[1]
Calculate the amount of sodium hydroxide in the mean titre.
[1]
Determine the concentration of ethanedioic acid.
[1]
Question 34
Copper(II) sulfate solution reacts with sodium hydroxide solution.
[\ce{CuSO4(aq) + 2NaOH(aq) -> Cu(OH)2
- Na2SO4(aq)}]
50.0 cm³ of (0.100, ext{mol dm}^{-3}) (\ce{CuSO4}) is mixed with 80.0 cm³ of (0.150, ext{mol dm}^{-3}) (\ce{NaOH}).
[1]
Calculate the amounts of both reactants.
[1]
Identify the limiting reactant.
[1]
Determine the theoretical amount of (\ce{Cu(OH)2}), in mol.
[1]
Question 35
Aspirin, (\ce{C9H8O4}), is prepared in a synthesis. The theoretical amount of aspirin is 0.0185 mol. The mass of dry aspirin obtained is 2.84 g.
Use (M(\ce{C9H8O4})=180.17, ext{g mol}^{-1}).
Calculate the theoretical mass of aspirin.
[1]
Calculate the percentage yield.
[1]
Suggest why recrystallisation may decrease the percentage yield while improving the product.
[1]
Question 36
Phenylamine can be prepared by reducing nitrobenzene.
[\ce{C6H5NO2 + 3H2 -> C6H7N + 2H2O}]
Use (M(\ce{C6H5NO2})=123.11), (M(\ce{H2})=2.02), (M(\ce{C6H7N})=93.13), (M(\ce{H2O})=18.02) in ( ext{g mol}^{-1}).
Calculate the atom economy for phenylamine.
[1]
State the relationship between atom economy and wastage for this reaction.
[1]
State one factor, other than atom economy, used to assess process efficiency.
[1]
Question 37
A mixture of gases reacts according to the equation:
[\ce{2NO
- O2
[1]
-> 2NO2(g)}]
At the same temperature and pressure, 60.0 cm³ of (\ce{NO}) is mixed with 40.0 cm³ of (\ce{O2}).
[1]
Identify the limiting gas.
[1]
Determine the volume of (\ce{NO2}) formed.
[1]
Determine the volume and identity of gas remaining after reaction.
[2]
Question 38
Zinc reacts with silver nitrate solution.
[\ce{Zn
- 2AgNO3(aq) -> Zn(NO3)2(aq) + 2Ag(s)}]
1.20 g of zinc is added to 50.0 cm³ of (0.500, ext{mol dm}^{-3}) silver nitrate.
Use (M(\ce{Zn})=65.38, ext{g mol}^{-1}).
[1]
Calculate the amount of zinc.
[1]
Calculate the amount of silver nitrate.
[1]
Identify the limiting reactant and calculate the amount of silver formed.
[1]
Question 39
A student investigates the reaction between zinc and copper(II) sulfate solution.
[\ce{Zn
| Trial | Mass of Zn / g | CuSO4 volume / cm3 | CuSO4 conc. / mol dm-3 | Mass of Cu collected / g |
|---|---|---|---|---|
| 1 | 0.250 | 25.0 | 0.100 | 0.229 |
| 2 | 0.500 | 50.0 | 0.100 | 0.326 |
| 3 | 0.500 | 75.0 | 0.100 | 0.454 |
| 4 | 0.750 | 50.0 | 0.100 | 0.309 |
- CuSO4(aq) -> ZnSO4(aq) + Cu(s)}]
The table shows initial quantities and the mass of copper collected after drying for several trials.
[1]
For trial 2, determine the limiting reactant using the data.
[1]
Calculate the percentage yield of copper for trial 2.
[1]
Evaluate whether the drying of the product in trial 2 was complete.
[1]
Question 40
The table compares three industrial routes to the same desired product. It includes atom economy, percentage yield and selected process information.
| Route | Atom economy / % | Yield / % | Solvent hazard | Energy / MJ kg⁻¹ | By-product treatment |
|---|---|---|---|---|---|
| A | 92 | 61 | High | 14.0 | Specialist disposal |
| B | 78 | 86 | Low | 8.5 | Recycled salt stream |
| C | 61 | 91 | Moderate | 12.0 | Neutralisation required |
Identify the route that produces the least stoichiometric waste.
[1]
Explain why the route with the highest atom economy may not give the greatest mass of product in practice.
[1]
Suggest which route is most suitable overall, using two pieces of evidence from the data.
[1]
Question 41
A gaseous hydrocarbon (\ce{CxHy}) undergoes complete combustion. The graph shows the volume of (\ce{CO2}) produced from different volumes of the hydrocarbon, with all gases measured at the same temperature and pressure.
Determine the gradient of the graph.
[1]
Use the gradient to determine the value of (x).
[1]
Explain why this method determines the number of carbon atoms in the hydrocarbon.
[1]
Question 42
Calcium carbonate reacts with hydrochloric acid.
[\ce{CaCO3
- 2HCl(aq) -> CaCl2(aq) + CO2
[1]
- H2O(l)}]
A student reacts 2.50 g of (\ce{CaCO3}) with 50.0 cm³ of (0.800, ext{mol dm}^{-3}) (\ce{HCl}).
Use (M(\ce{CaCO3})=100.09, ext{g mol}^{-1}) and (V_m=22.7, ext{dm}^3, ext{mol}^{-1}) at STP.
[1]
Determine the limiting reactant.
[1]
Calculate the theoretical volume of (\ce{CO2}) at STP and discuss one reason why the measured volume may be lower.
[1]
Question 43
Two reactions can make ethanol.
Route A:
[\ce{C2H4
- H2O
[1]
-> C2H5OH(l)}]
Route B:
[\ce{C6H12O6(aq) -> 2C2H5OH(aq) + 2CO2(g)}]
Use (M(\ce{C2H4})=28.05), (M(\ce{H2O})=18.02), (M(\ce{C2H5OH})=46.07), (M(\ce{C6H12O6})=180.18) in ( ext{g mol}^{-1}).
[1]
Calculate the atom economy for ethanol for each route.
[1]
Compare the two routes as green chemistry processes, referring to atom economy and two other factors.
[1]
Question 44
Butane undergoes complete combustion.
Deduce the balanced equation for the complete combustion of butane, (\ce{C4H10}), including state symbols.
[1]
camping stove burns 2.90 g of butane completely. Calculate the volume of (\ce{CO2}) produced at STP and explain the mole-ratio steps used. Use (M(\ce{C4H10})=58.14, ext{g mol}^{-1}) and (V_m=22.7, ext{dm}^3, ext{mol}^{-1}).
[1]
Question 45
Students prepared a crystalline product and recorded mass and melting-point data before and after recrystallisation. A literature melting point is provided.
| Quantity | Mass / g | Melting data / °C |
|---|---|---|
| Theoretical product | 2.50 | |
| Crude product | 2.18 | 117–123 |
| Recrystallised product | 1.74 | 126–128 |
| Literature value | 128 |
Calculate the percentage yield after recrystallisation.
[1]
Compare the purity of the crude and recrystallised samples using the melting-point data.
[1]
Evaluate whether the recrystallisation improved the product overall.
[1]
Question 46
A student prepares silver chloride by mixing silver nitrate and sodium chloride solutions.
[\ce{AgNO3(aq) + NaCl(aq) -> AgCl
- NaNO3(aq)}]
25.0 cm³ of (0.200, ext{mol dm}^{-3}) (\ce{AgNO3}) is mixed with 40.0 cm³ of (0.150, ext{mol dm}^{-3}) (\ce{NaCl}). The dry mass of (\ce{AgCl}) collected is 0.650 g.
Use (M(\ce{AgCl})=143.32, ext{g mol}^{-1}).
[1]
Determine the limiting reactant.
[1]
Calculate the theoretical yield and percentage yield, and explain whether the yield is plausible.
[1]
Question 47
An industrial company compares two routes for making propanone.
Route 1:
[\ce{C3H8O -> C3H6O + H2}]
Route 2:
[\ce{C3H6 + H2O + [O] -> C3H6O + H2O}]
Assume the desired product is (\ce{C3H6O}). Use (M(\ce{C3H8O})=60.10), (M(\ce{C3H6O})=58.08), (M(\ce{H2})=2.02), (M(\ce{C3H6})=42.08), (M(\ce{H2O})=18.02), and (M([O])=16.00) in ( ext{g mol}^{-1}).
Calculate the atom economy for propanone for each route.
[1]
Evaluate which route is greener overall, using atom economy and three other relevant factors.
[1]
Question 48
Iron can be extracted from iron(III) oxide using carbon monoxide.
[\ce{Fe2O3
- 3CO
[1]
-> 2Fe
[1]
- 3CO2(g)}]
A furnace charge contains 1.20 kg of (\ce{Fe2O3}) and 420 g of (\ce{CO}).
Use (M(\ce{Fe2O3})=159.69), (M(\ce{CO})=28.01), and (M(\ce{Fe})=55.85) in ( ext{g mol}^{-1}).
[1]
Determine the limiting reactant.
[1]
Calculate the theoretical mass of iron and explain the meaning of theoretical yield in this context.
[1]
Question 49
A student determines the concentration of hydrochloric acid by reacting it with sodium carbonate.
[\ce{Na2CO3(aq) + 2HCl(aq) -> 2NaCl(aq) + CO2
- H2O(l)}]
25.00 cm³ of (0.0500, ext{mol dm}^{-3}) sodium carbonate requires 21.35 cm³ of hydrochloric acid for complete reaction.
[1]
Calculate the concentration of hydrochloric acid.
[1]
The student instead tries to determine the concentration by collecting carbon dioxide gas. Evaluate this alternative method, referring to stoichiometry and practical limitations.
[1]
Question 50
A student synthesizes magnesium oxide by heating magnesium in a crucible.
[\ce{2Mg
- O2
[1]
-> 2MgO(s)}]
0.486 g of magnesium is heated. The final mass of magnesium oxide recorded is 0.835 g.
Use (M(\ce{Mg})=24.31, ext{g mol}^{-1}) and (M(\ce{MgO})=40.31, ext{g mol}^{-1}).
[1]
Calculate the theoretical mass of magnesium oxide.
[1]
Calculate the percentage yield and discuss two possible experimental causes of the result.
[1]
The Fast Track To Your
Best IB Coursework & College Essays
All content on this website has been developed independently from and is not endorsed by the International Baccalaureate Organization. International Baccalaureate and IB are registered trademarks owned by the International Baccalaureate Organization.