R2.1 How much? The amount of chemical change - IB Chemistry Question Bank

Question 1

SL • Paper 1A

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SL • Paper 1A

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What is the sum of the coefficients when the equation is balanced using the simplest whole-number ratio?

$\underline{\hspace{1em}}\,\text{Al}(s) + \underline{\hspace{1em}}\,\text{HCl}(aq) \to \underline{\hspace{1em}}\,\text{AlCl}_3(aq) + \underline{\hspace{1em}}\,H_2(g)$

A.

$14$

B.

$13$

C.

$10$

D.

$11$

Question 2

SL • Paper 1A

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SL • Paper 1A

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The theoretical yield of a product is $6.50\ \text{g}$ . The experimental yield is $5.20\ \text{g}$ .

What is the percentage yield?

A.

$125\ \%$

B.

$80.0\ \%$

C.

$65.0\ \%$

D.

$100\ \%$

Question 3

SL • Paper 1A

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SL • Paper 1A

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Sodium carbonate solution reacts with hydrochloric acid solution to form sodium chloride solution, water and carbon dioxide gas.

The correct equation, including state symbols, is:

A.

$\text{Na}_2\text{CO}_3(aq) + 2\text{HCl}(aq) \to 2\text{NaCl}(aq) + H_2O(l) + CO_2(g)$

B.

$\text{Na}_2\text{CO}_3(l) + 2\text{HCl}(aq) \to 2\text{NaCl}(s) + H_2O(l) + CO_2(g)$

C.

$\text{NaCO}_3(aq) + \text{HCl}(aq) \to \text{NaCl}(aq) + H_2O(l) + CO_2(g)$

D.

$\text{Na}_2\text{CO}_3(aq) + \text{HCl}(aq) \to \text{NaCl}(aq) + H_2O(l) + CO_2(aq)$

Question 4

SL • Paper 1A

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SL • Paper 1A

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Calcium carbonate decomposes on heating.

$\text{CaCO}_3(s) \to \text{CaO}(s) + CO_2(g)$

What mass of $CO_2$ is formed from complete decomposition of $10.0\ \text{g}$ of $\text{CaCO}_3$ ?

Use $M_r(\text{CaCO}_3)=100.09$ and $M_r(CO_2)=44.01$ .

A.

$4.40\ \text{g}$

B.

$2.20\ \text{g}$

C.

$5.60\ \text{g}$

D.

$10.0\ \text{g}$

Question 5

SL • Paper 1A

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SL • Paper 1A

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Ethene burns completely in oxygen.

$C_2H_4(g) + 3O_2(g) \to 2CO_2(g) + 2H_2O(g)$

What volume of oxygen reacts with $25.0\ \text{cm}^3$ of ethene at the same temperature and pressure?

A.

$12.5\ \text{cm}^3$

B.

$75.0\ \text{cm}^3$

C.

$25.0\ \text{cm}^3$

D.

$50.0\ \text{cm}^3$

Question 6

HL • Paper 1A

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HL • Paper 1A

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A reaction has a high atom economy but a low percentage yield.

The correct interpretation is:

A.

Most reactant atoms are in the desired product according to the equation, but little of the theoretical product is obtained experimentally.

B.

The experimental yield is greater than the theoretical yield because the reactants are efficiently converted.

C.

The reaction must be green because percentage yield is not relevant to waste production.

D.

Most reactant atoms become waste, but the experimental yield is close to the theoretical yield.

Question 7

SL • Paper 2

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SL • Paper 2

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Aqueous barium chloride reacts with aqueous sodium sulfate to form a precipitate of barium sulfate and aqueous sodium chloride.

A

Deduce the balanced chemical equation for the reaction, including state symbols.

[2]

B

State the mole ratio of barium chloride to barium sulfate.

[1]

Question 8

SL • Paper 1A

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SL • Paper 1A

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A $25.00\ \text{cm}^3$ sample of sulfuric acid is exactly neutralized by $18.60\ \text{cm}^3$ of $0.100\ \text{mol dm}^{-3}$ potassium hydroxide.

$H_2SO_4(aq) + 2\text{KOH}(aq) \to \text{K}_2\text{SO}_4(aq) + 2H_2O(l)$

What is the concentration of the sulfuric acid?

A.

$0.0744\ \text{mol dm}^{-3}$

B.

$0.0372\ \text{mol dm}^{-3}$

C.

$0.0186\ \text{mol dm}^{-3}$

D.

$0.186\ \text{mol dm}^{-3}$

Question 9

HL • Paper 1A

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HL • Paper 1A

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Aluminium reacts with chlorine to form aluminium chloride.

$2\text{Al}(s) + 3\text{Cl}_2(g) \to 2\text{AlCl}_3(s)$

A mixture contains $5.40\ \text{g}$ of aluminium and $14.2\ \text{g}$ of chlorine. What is the limiting reactant and the theoretical mass of aluminium chloride formed?

Use $M(\text{Al})=26.98\ \text{g mol}^{-1}$ , $M(\text{Cl}_2)=70.90\ \text{g mol}^{-1}$ and $M(\text{AlCl}_3)=133.33\ \text{g mol}^{-1}$ .

A.

Chlorine; $17.8\ \text{g}$

B.

Aluminium; $26.7\ \text{g}$

C.

Chlorine; $26.7\ \text{g}$

D.

Aluminium; $17.8\ \text{g}$

Question 10

HL • Paper 1A

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HL • Paper 1A

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Calcium chloride is the desired product in the reaction shown.

$\text{CaCO}_3(s) + 2\text{HCl}(aq) \to \text{CaCl}_2(aq) + H_2O(l) + CO_2(g)$

What is the atom economy for calcium chloride?

Use $M(\text{CaCO}_3)=100.09\ \text{g mol}^{-1}$ , $M(\text{HCl})=36.46\ \text{g mol}^{-1}$ and $M(\text{CaCl}_2)=110.98\ \text{g mol}^{-1}$ .

A.

$36.0\ \%$

B.

$64.1\ \%$

C.

$56.1\ \%$

D.

$73.5\ \%$

Question 11

HL • Paper 1A

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HL • Paper 1A

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Ethyl ethanoate is the desired product in the reaction shown.

$C_2H_5OH + CH_3COOH \to CH_3COOC_2H_5 + H_2O$

What is the atom economy for ethyl ethanoate?

Use $M(C_2H_5OH)=46.08\ \text{g mol}^{-1}$ , $M(CH_3COOH)=60.06\ \text{g mol}^{-1}$ and $M(CH_3COOC_2H_5)=88.12\ \text{g mol}^{-1}$ .

A.

$100\ \%$

B.

$73.4\ \%$

C.

$83.0\ \%$

D.

$54.9\ \%$

Question 12

HL • Paper 1A

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HL • Paper 1A

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Nitrogen and hydrogen react completely to form ammonia.

$N_2(g) + 3H_2(g) \to 2NH_3(g)$

$40\ \text{cm}^3$ of nitrogen is mixed with $90\ \text{cm}^3$ of hydrogen at the same temperature and pressure. What is the total gas volume after reaction, assuming ammonia remains gaseous?

A.

$90\ \text{cm}^3$

B.

$60\ \text{cm}^3$

C.

$130\ \text{cm}^3$

D.

$70\ \text{cm}^3$

Question 13

SL • Paper 2

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SL • Paper 2

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Zinc reacts with hydrochloric acid according to the equation:

$\text{Zn}_{(s)} + 2\text{HCl}_{(aq)} \to \text{ZnCl}_{2(aq)} + \text{H}_{2(g)}$

A student reacts $0.650\ \text{g}$ of zinc with excess hydrochloric acid. The molar volume of a gas at STP is $22.7\ \text{dm}^3\ \text{mol}^{-1}$ .

A

Calculate the amount, in mol, of zinc used.

[1]

B

Calculate the amount, in mol, of hydrochloric acid required to react exactly with this amount of zinc.

[1]

C

Calculate the volume, in $\text{dm}^3$ , of hydrogen produced at STP.

[2]

Question 14

SL • Paper 2

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SL • Paper 2

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Sulfuric acid is titrated with sodium hydroxide solution.

$\text{H}_2\text{SO}_{4(aq)} + 2\text{NaOH}_{(aq)} \to \text{Na}_2\text{SO}_{4(aq)} + 2\text{H}_2\text{O}_{(l)}$

A $25.00\ \text{cm}^3$ sample of sulfuric acid is exactly neutralized by $23.60\ \text{cm}^3$ of $0.1000\ \text{mol dm}^{-3}$ sodium hydroxide.

A

Calculate the amount, in mol, of sodium hydroxide used.

[1]

B

Calculate the concentration of the sulfuric acid.

[2]

Question 15

SL • Paper 2

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SL • Paper 2

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Calcium carbonate is precipitated when calcium chloride solution reacts with sodium carbonate solution.

$\text{CaCl}_{2(aq)} + \text{Na}_2\text{CO}_{3(aq)} \to \text{CaCO}_{3(s)} + 2\text{NaCl}_{(aq)}$

A $25.0\ \text{cm}^3$ sample of $0.200\ \text{mol dm}^{-3}$ calcium chloride is reacted with excess sodium carbonate. The dry mass of calcium carbonate collected is $0.478\ \text{g}$ .

A

Calculate the theoretical yield of calcium carbonate, in g.

[2]

B

Calculate the percentage yield.

[1]

Question 16

SL • Paper 1B

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SL • Paper 1B

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A gaseous hydrocarbon is burned completely in oxygen. The stimulus shows the formula of the hydrocarbon and gas-volume data collected at the same temperature and pressure.

Gas	Formula / state	Volume / cm³
hydrocarbon	$C_3H_8$ (g)	50.0
oxygen	$O_2$ (g)	250.0

A

Deduce the balanced equation, including state symbols, for the complete combustion of the hydrocarbon shown.

[2]

B

Calculate the volume of carbon dioxide formed from the volume of hydrocarbon shown in the stimulus.

[1]

C

Explain why the same coefficient ratio cannot be used directly to calculate the volume of liquid water produced.

[1]

Question 17

SL • Paper 1B

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SL • Paper 1B

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A student determined the concentration of sulfuric acid by titration with sodium hydroxide. The stimulus shows the equation and titration data.

Measurement / unit	Value
Balanced equation	$H_2SO_4 + 2\text{NaOH} \to \text{Na}_2\text{SO}_4 + 2H_2O$
NaOH solution concentration / mol dm-3	0.100
Sulfuric acid aliquot / cm3	25.00
Rough titre / cm3	24.20
Titre 1 / cm3	24.59
Titre 2 / cm3	24.61

A

Calculate the mean titre from the concordant titres in the stimulus.

[1]

B

Calculate the concentration of the sulfuric acid.

[2]

C

State the role of the indicator in this titration.

[1]

Question 18

SL • Paper 1B

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SL • Paper 1B

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Calcium carbonate was heated strongly until no further visible change occurred. The stimulus shows the decomposition equation and mass data for the solid product.

Quantity	Value
Thermal decomposition	$CaCO_3(s) \to CaO(s) + CO_2(g)$
Calcium carbonate used / g	2.50
Solid product after heating / g	1.29

A

Distinguish between the theoretical yield and the experimental yield in this experiment.

[1]

B

Calculate the theoretical mass of calcium oxide formed from the calcium carbonate used.

[2]

C

Calculate the percentage yield using the mass of solid product in the stimulus.

[1]

Question 19

HL • Paper 1A

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HL • Paper 1A

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A $50.0\ \text{cm}^3$ sample of $0.200\ \text{mol dm}^{-3}$ barium chloride is mixed with $40.0\ \text{cm}^3$ of $0.300\ \text{mol dm}^{-3}$ sodium sulfate.

$\text{BaCl}_2(aq) + \text{Na}_2\text{SO}_4(aq) \to \text{BaSO}_4(s) + 2\text{NaCl}(aq)$

After complete precipitation, what is the concentration of excess sulfate ions in the final solution? Assume volumes are additive.

A.

$0.0100\ \text{mol dm}^{-3}$

B.

$0.133\ \text{mol dm}^{-3}$

C.

$0.0222\ \text{mol dm}^{-3}$

D.

$0.0444\ \text{mol dm}^{-3}$

Question 20

SL • Paper 2

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SL • Paper 2

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Aluminium reacts with iron(III) oxide in the thermite reaction.

$2\text{Al}_{(s)} + \text{Fe}_2\text{O}_{3(s)} \to \text{Al}_2\text{O}_{3(s)} + 2\text{Fe}_{(l)}$

A mixture contains $4.00\ \text{g}$ of aluminium and $12.0\ \text{g}$ of iron(III) oxide.

A

Determine the limiting reactant.

[2]

B

Calculate the theoretical mass of iron produced.

[2]

Question 21

SL • Paper 2

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SL • Paper 2

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Ethanol can be produced by different reactions.

Reaction 1: $\text{C}_2\text{H}_4 + \text{H}_2\text{O} \to \text{C}_2\text{H}_5\text{OH}$

Reaction 2: $\text{C}_2\text{H}_5\text{Br} + \text{NaOH} \to \text{C}_2\text{H}_5\text{OH} + \text{NaBr}$

Ethanol is the desired product in both reactions.

A

Calculate the atom economy for Reaction 2.

[2]

B

State the atom economy for Reaction 1 and outline its relationship to wastage.

[2]

Question 22

HL • Paper 2

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HL • Paper 2

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Nitrogen and hydrogen react to form ammonia.

$\text{N}_{2(g)} + 3\text{H}_{2(g)} \to 2\text{NH}_{3(g)}$

$12.0\ \text{dm}^3$ of nitrogen is mixed with $30.0\ \text{dm}^3$ of hydrogen at the same temperature and pressure.

Gas	Initial volume / $\text{dm}^{3}$
$N_2(g)$	12.0
$H_2(g)$	30.0

A

Determine the limiting reactant.

[2]

B

Calculate the maximum volume of ammonia formed and the volume of excess gas remaining, assuming complete reaction.

[2]

Question 23

HL • Paper 2

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HL • Paper 2

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A sample of hydrated copper(II) sulfate, $\text{CuSO}_4 \cdot x\text{H}_2\text{O}$ , has a mass of $2.495\ \text{g}$ . It is heated to constant mass, leaving $1.596\ \text{g}$ of anhydrous $\text{CuSO}_4$ .

A

Calculate the amount, in mol, of anhydrous copper(II) sulfate.

[1]

B

Calculate the amount, in mol, of water removed.

[2]

C

Determine the value of $x$ in $\text{CuSO}_4 \cdot x\text{H}_2\text{O}$ .

[1]

Question 24

HL • Paper 2

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HL • Paper 2

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Two routes for preparing ethanoic acid are shown.

Route A: $\text{CH}_3\text{OH} + \text{CO} \to \text{CH}_3\text{COOH}$

Route B: $\text{C}_2\text{H}_5\text{OH} + \text{O}_2 \to \text{CH}_3\text{COOH} + \text{H}_2\text{O}$

Ethanoic acid is the desired product.

A two-path reaction scheme comparing Route A and Route B to ethanoic acid, showing reactant names/formulae and by-product formation without giving atom economy values.

A

Calculate the atom economy for Route B.

[2]

B

Evaluate which route is more efficient in terms of atom economy, and state one other factor that should be considered when assessing overall process efficiency.

[2]

Question 25

SL • Paper 1B

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SL • Paper 1B

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A precipitate of silver chloride is formed by mixing aqueous silver nitrate with aqueous sodium chloride. The stimulus shows the balanced equation and experimental data.

Information	Details
Balanced equation	$\text{AgNO}_3$ (aq) + $\text{NaCl}$ (aq) $\to$ $\text{AgCl}$ (s) + $\text{NaNO}_3$ (aq)
Silver nitrate solution	$0.200\ \text{mol dm}^{-3}$ , $20.0\ \text{cm}^3$
Sodium chloride solution	$0.120\ \text{mol dm}^{-3}$ , $25.0\ \text{cm}^3$
Collected dry silver chloride	$0.392\ \text{g}$

A

Identify the limiting reactant. Show your working.

[2]

B

Calculate the theoretical mass of silver chloride that could form.

[2]

C

Calculate the percentage yield using the collected dry mass in the stimulus.

[1]

Question 26

SL • Paper 1B

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SL • Paper 1B

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Magnesium reacts with excess hydrochloric acid to form hydrogen gas. The graph shows the volume of hydrogen collected against time. The molar volume of gas under the laboratory conditions is given in the stimulus.

Hydrogen volume collected as magnesium reacts with excess hydrochloric acid.

A

Use the plateau volume to calculate the experimental amount of hydrogen produced.

[1]

B

Calculate the theoretical volume of hydrogen from the mass of magnesium used.

[2]

C

Suggest one reason why the experimental volume is lower than the theoretical volume.

[1]

Question 27

SL • Paper 1B

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SL • Paper 1B

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Hydrogen can be produced by different reactions. The stimulus compares two reactions where hydrogen is the desired product.

Process	Equation	Species and $M_r$ / g mol $^{-1}$	Yield / %	Conditions
Steam reforming	$CH_4$ (g) + $H_2O$ (g) $\to$ $CO$ (g) + $3H_2$ (g)	$CH_4$ 16.05; $H_2O$ 18.02; $CO$ 28.01; $H_2$ 2.02	75	$800^\circ\text{C}$ , Ni catalyst
Water electrolysis	$2H_2O$ (l) $\to$ $2H_2$ (g) + $O_2$ (g)	$H_2O$ 18.02; $H_2$ 2.02; $O_2$ 32.00	90	Electric current, room temp

A

Calculate the atom economy for the reaction $CH_4(g)+H_2O(g)\to CO(g)+3H_2(g)$ when hydrogen is the desired product.

[2]

B

Explain the relationship between atom economy and wastage for the two reactions in the stimulus.

[1]

C

Suggest one factor, other than atom economy and percentage yield, that should be considered when judging which process is greener.

[1]

Question 28

HL • Paper 2

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HL • Paper 2

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Aqueous silver nitrate is mixed with aqueous sodium chloride.

$\text{AgNO}_{3(aq)} + \text{NaCl}_{(aq)} \to \text{AgCl}_{(s)} + \text{NaNO}_{3(aq)}$

$35.0\ \text{cm}^3$ of $0.120\ \text{mol dm}^{-3}$ silver nitrate is mixed with $50.0\ \text{cm}^3$ of $0.0750\ \text{mol dm}^{-3}$ sodium chloride.

A

Determine the limiting reactant.

[2]

B

Calculate the mass of silver chloride formed.

[1]

C

Calculate the concentration of nitrate ions in the final solution after the precipitate is removed. Assume volumes are additive.

[1]

Question 29

HL • Paper 2

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HL • Paper 2

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An impure sample of sodium carbonate is analysed by titration.

$\text{Na}_2\text{CO}_{3(aq)} + 2\text{HCl}_{(aq)} \to 2\text{NaCl}_{(aq)} + \text{H}_2\text{O}_{(l)} + \text{CO}_{2(g)}$

A $0.212\ \text{g}$ sample requires $32.40\ \text{cm}^3$ of $0.1000\ \text{mol dm}^{-3}$ hydrochloric acid for complete reaction.

A

Calculate the amount, in mol, of hydrochloric acid used.

[1]

B

Calculate the mass of sodium carbonate in the sample.

[2]

C

Calculate the percentage purity of the sodium carbonate sample.

[1]

Question 30

HL • Paper 2

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HL • Paper 2

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An impure sample of sodium hydrogencarbonate reacts with excess hydrochloric acid.

$\text{NaHCO}_{3(s)} + \text{HCl}_{(aq)} \to \text{NaCl}_{(aq)} + \text{H}_2\text{O}_{(l)} + \text{CO}_{2(g)}$

A $1.20\ \text{g}$ sample produces $0.285\ \text{dm}^3$ of carbon dioxide at STP. The molar volume of a gas at STP is $22.7\ \text{dm}^3\ \text{mol}^{-1}$ .

A

Calculate the amount, in mol, of carbon dioxide produced.

[1]

B

Calculate the percentage by mass of sodium hydrogencarbonate in the sample.

[2]

C

Suggest one experimental reason why the collected gas volume could be lower than the theoretical volume.

[1]

Question 31

HL • Paper 1B

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HL • Paper 1B

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An antacid tablet containing calcium carbonate was analysed by back titration. The tablet was reacted with excess hydrochloric acid, and the remaining acid was titrated with sodium hydroxide. The stimulus shows the relevant equations and data.

Item	Value	Unit
Mass of antacid tablet	0.500	g
Hydrochloric acid added	0.200	$\text{mol dm}^{-3}$
Volume of hydrochloric acid added	50.00	$\text{cm}^3$
Sodium hydroxide used in back titration	0.100	$\text{mol dm}^{-3}$
Volume of sodium hydroxide used	18.40	$\text{cm}^3$
Reaction with calcium carbonate	$\text{CaCO}_3 + 2\text{HCl} \to \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O}$
Back titration reaction	$\text{HCl} + \text{NaOH} \to \text{NaCl} + \text{H}_2\text{O}$

A

Calculate the amount of hydrochloric acid initially added to the tablet.

[1]

B

Calculate the amount of hydrochloric acid that reacted with calcium carbonate.

[2]

C

Calculate the percentage by mass of calcium carbonate in the tablet.

[2]

Question 32

HL • Paper 1B

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HL • Paper 1B

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Aspirin can be prepared by reacting salicylic acid with ethanoic anhydride. The stimulus shows the equation, reagent data and melting range data for crude and recrystallized product.

Item	Quantity	Molar mass / g mol $^{-1}$	Density / g mL $^{-1}$	Melting range / $^\circ\text{C}$
Equation	salicylic acid + ethanoic anhydride $\to$ aspirin + ethanoic acid
Stoich. ratio	1:1
Salicylic acid	2.00 g	138.13
Ethanoic anhydride	5.00 mL	102.09	1.08
Crude aspirin	2.40 g	180.16		128-134
Recrystallized aspirin	2.05 g	180.16		135-136
Literature aspirin				135-136

A

Identify the limiting reactant. Show your working.

[2]

B

Calculate the percentage yield of recrystallized aspirin.

[2]

C

Evaluate whether recrystallization improved the product, using the mass and melting range data.

[1]

Question 33

HL • Paper 1B

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HL • Paper 1B

Hard

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Two processes for producing ethene oxide, $C_2H_4O$ , are compared in the stimulus. Ethene oxide is the desired product.

Route	Overall equation	Percentage yield / %
Direct oxidation	$2C_2H_4$ (g) + $O_2$ (g) $\to$ $2C_2H_4O$ (g)	60
Chlorination route	$C_2H_4$ (g) + $Cl_2$ (g) + $2NaOH$ (aq) $\to$ $C_2H_4O$ (g) + $2NaCl$ (aq) + $H_2O$ (l)	80

A

Calculate the atom economy for $C_2H_4(g)+Cl_2(g)+2NaOH(aq)\to C_2H_4O(g)+2NaCl(aq)+H_2O(l)$ .

[2]

B

Compare the two processes using atom economy and percentage yield.

[2]

C

Suggest why the process with the higher percentage yield may still be less suitable industrially.

[1]

Question 34

HL • Paper 1B

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HL • Paper 1B

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Aqueous barium hydroxide and hydrochloric acid were mixed. The reaction was assumed to go to completion and volumes were treated as additive. The stimulus shows an initial-change-final table with some entries omitted.

Solution	Concentration / mol dm $^{-3}$	Volume / cm $^3$
Ba(OH)2(aq)	0.120	35.0
HCl(aq)	0.150	50.0
Total after mixing	—	85.0

A

Calculate the initial amounts of barium hydroxide and hydrochloric acid.

[2]

B

Identify the excess reactant and calculate its amount remaining after reaction.

[2]

C

Calculate the final concentration of hydroxide ions in the mixture.

[1]

Question 35

SL • Paper 2

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SL • Paper 2

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A sample of impure calcium carbonate was analysed by adding excess hydrochloric acid. The calcium carbonate reacts according to the equation:

$CaCO_3(s) + 2HCl(aq) \to CaCl_2(aq) + CO_2(g) + H_2O(l)$

A $2.50\ \text{g}$ sample was added to $100.0\ \text{cm}^3$ of $0.250\ \text{mol dm}^{-3}$ hydrochloric acid. The acid remaining after reaction required $18.60\ \text{cm}^3$ of $0.100\ \text{mol dm}^{-3}$ sodium hydroxide for neutralisation.

A

The back titration is based on acid remaining after the carbonate has reacted.

I.

Explain why the hydrochloric acid must be in excess for this method to determine the amount of calcium carbonate in the sample.

[2]

II.

Calculate the amount, in mol, of hydrochloric acid initially added.

[1]

B

I.

Calculate the amount, in mol, of hydrochloric acid remaining after reaction with the calcium carbonate.

[1]

II.

Determine the percentage by mass of calcium carbonate in the impure sample.

[2]

C

The sample was not dried before weighing. State and explain how this affects the calculated percentage by mass of calcium carbonate.

[2]

Question 36

SL • Paper 2

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SL • Paper 2

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Nitrogen and hydrogen react to form ammonia according to the equation:

$N_2(g) + 3H_2(g) \to 2NH_3(g)$

A mixture contains $4.50\ \text{dm}^3$ of nitrogen and $10.0\ \text{dm}^3$ of hydrogen at the same temperature and pressure.

A

The gases are mixed and allowed to react as completely as possible.

I.

State why gas volumes can be compared directly in this calculation.

[1]

II.

Determine the limiting reactant.

[2]

B

I.

Calculate the theoretical volume of ammonia formed.

[1]

II.

The experimental volume of ammonia collected is $5.80\ \text{dm}^3$ at the same temperature and pressure. Calculate the percentage yield.

[1]

C

Explain why the theoretical yield is not the same as the experimental yield in many reactions.

[2]

Question 37

SL • Paper 2

Hard

Calculator Permitted

SL • Paper 2

Hard

Calculator Permitted

Ethanol can be manufactured by different processes.

Process 1: $C_2H_4(g) + H_2O(g) \to C_2H_5OH(g)$

Process 2: $C_6H_{12}O_6(aq) \to 2C_2H_5OH(aq) + 2CO_2(g)$

In each process, ethanol is the desired product.

Process	Equation	Total Mr of reactants / g mol $^{-1}$	Mr of ethanol formed / g mol $^{-1}$	Mr of other products / g mol $^{-1}$
1	$C_2H_4(g) + H_2O(g) \to C_2H_5OH(g)$	46.08	46.08	0
2	$C_6H_{12}O_6(aq) \to 2C_2H_5OH(aq) + 2CO_2(g)$	180.18	92.16	88.02

A

Atom economy is one measure of the efficiency of a chemical process.

I.

Calculate the atom economy for Process 1.

[1]

II.

Calculate the atom economy for Process 2.

[2]

B

Compare the two processes in terms of atom economy and wastage.

[2]

C

Evaluate why atom economy alone is insufficient for deciding which process is greener.

[2]

Question 38

HL • Paper 1B

Hard

Calculator Permitted

HL • Paper 1B

Hard

Calculator Permitted

A gaseous mixture of methane and ethane was completely burned in oxygen. All gas volumes were measured at the same temperature and pressure after water vapour had condensed. The stimulus shows gas-volume data.

Gas	Volume / $\text{cm}^{3}$
Methane + ethane mixture	20.0
Carbon dioxide formed	34.0

A

Determine the volumes of methane and ethane in the original mixture.

[3]

B

Use your answer to calculate the oxygen volume required for complete combustion.

[1]

C

Suggest one reason why a measured oxygen consumption could be slightly different from the calculated value.

[1]

Question 39

HL • Paper 1B

Hard

Calculator Permitted

HL • Paper 1B

Hard

Calculator Permitted

Sodium hydrogencarbonate decomposes on heating. Repeated heating mass data are shown in the stimulus.

Heating cycle	Mass of solid / g
0	3.00
1	2.31
2	2.02
3	1.92
4	1.89
5	1.89

A

Use the mass data to identify the decomposition equation best supported by the experiment.

[2]

B

Calculate the theoretical mass of solid residue from the initial mass of sodium hydrogencarbonate.

[2]

C

A separate trial gave a final residue mass greater than the theoretical mass. Suggest one experimental reason.

[1]

Question 40

SL • Paper 2

Hard

Calculator Permitted

SL • Paper 2

Hard

Calculator Permitted

Aqueous barium chloride and aqueous sodium sulfate are mixed to produce a precipitate of barium sulfate. A student mixes $25.0\ \text{cm}^3$ of $0.200\ \text{mol dm}^{-3}$ barium chloride with $40.0\ \text{cm}^3$ of $0.150\ \text{mol dm}^{-3}$ sodium sulfate.

A simple laboratory filtration setup showing a beaker containing a cloudy mixture being poured through filter paper in a funnel into a conical flask. The precipitate is retained on the filter paper and the filtrate is collected below. Labels should identify residue, filtrate, funnel and conical flask; no masses or calculated values are shown. No additional prompt text is shown.

A

The precipitate forms when barium ions and sulfate ions combine.

I.

Write the net ionic equation for the precipitation reaction, including state symbols.

[2]

II.

Identify the limiting reactant, showing your working.

[2]

B

I.

Calculate the theoretical mass of barium sulfate formed.

[1]

II.

The dried precipitate has a mass of $1.05\ \text{g}$ . Calculate the percentage yield.

[1]

C

Calculate the concentration of sulfate ions remaining in the filtrate after the precipitate is removed. Assume solution volumes are additive.

[2]

Question 41

SL • Paper 2

Hard

Calculator Permitted

SL • Paper 2

Hard

Calculator Permitted

Ethanol undergoes complete combustion in oxygen to form carbon dioxide and water. A sample contains $2.30\ \text{g}$ ethanol, $C_2H_5OH$ . In a second combustion, $3.00\ \text{dm}^3$ of oxygen is supplied at the same conditions. The molar volume of a gas at the stated conditions is $22.7\ \text{dm}^3\ \text{mol}^{-1}$ .

A

The complete combustion equation is required before reacting quantities can be calculated.

I.

Write the balanced equation for the complete combustion of ethanol.

[1]

II.

Calculate the amount, in mol, of ethanol in the sample.

[1]

B

I.

Calculate the volume of oxygen required for complete combustion of the ethanol sample.

[2]

II.

Calculate the volume of carbon dioxide produced by complete combustion of the ethanol sample.

[1]

C

A second combustion uses the same mass of ethanol but only $3.00\ \text{dm}^3$ oxygen at the same conditions.

I.

Identify the limiting reactant.

[1]

II.

Calculate the mass of ethanol remaining unreacted.

[2]

Question 42

SL • Paper 2

Hard

Calculator Permitted

SL • Paper 2

Hard

Calculator Permitted

A student determines the concentration of sulfuric acid by titration with sodium hydroxide.

$H_2SO_4(aq) + 2NaOH(aq) \to Na_2SO_4(aq) + 2H_2O(l)$

A $20.00\ \text{cm}^3$ sample of sulfuric acid requires $24.60\ \text{cm}^3$ of $0.0950\ \text{mol dm}^{-3}$ sodium hydroxide for complete neutralisation.

A titration setup with a burette delivering sodium hydroxide into a conical flask containing sulfuric acid and indicator. Labels identify burette, conical flask, sodium hydroxide solution and sulfuric acid sample. No numerical titre is displayed on the apparatus.

A

The titration data are used to determine the acid concentration.

I.

Calculate the amount, in mol, of sodium hydroxide used.

[1]

II.

Calculate the concentration of sulfuric acid.

[2]

B

The same sulfuric acid is used to react with calcium carbonate:

$CaCO_3(s) + H_2SO_4(aq) \to CaSO_4(s) + CO_2(g) + H_2O(l)$

I.

Calculate the mass of pure calcium carbonate required to react exactly with $250.0\ \text{cm}^3$ of the sulfuric acid.

[2]

II.

Calculate the volume of carbon dioxide produced at $22.7\ \text{dm}^3\ \text{mol}^{-1}$ .

[1]

C

Discuss why the volume ratio of sulfuric acid to sodium hydroxide in the titration is not sufficient by itself to determine the mole ratio in the equation.

[2]

Question 43

HL • Paper 2

Hard

Calculator Permitted

HL • Paper 2

Hard

Calculator Permitted

Aspirin, $C_9H_8O_4$ , can be prepared by reacting salicylic acid, $C_7H_6O_3$ , with ethanoic anhydride, $C_4H_6O_3$ :

$C_7H_6O_3(s) + C_4H_6O_3(l) \to C_9H_8O_4(s) + C_2H_4O_2(l)$

A student reacts $2.00\ \text{g}$ salicylic acid with $5.00\ \text{cm}^3$ ethanoic anhydride. The density of ethanoic anhydride is $1.08\ \text{g cm}^{-3}$ . The student obtains $2.18\ \text{g}$ aspirin after purification.

Substance	Formula	Amount / g or cm $^3$	Density / g cm $^{-3}$	Purified mass / g
Salicylic acid	$C_7H_6O_3$	$2.00\ \text{g}$	—	—
Ethanoic anhydride	$C_4H_6O_3$	$5.00\ \text{cm}^3$	$1.08$	—
Aspirin (product)	$C_9H_8O_4$	—	—	$2.18\ \text{g}$

A

The reaction mixture contains two reactants in a $1:1$ mole ratio.

I.

Determine the limiting reactant.

[3]

II.

Calculate the theoretical mass of aspirin.

[1]

B

I.

Calculate the percentage yield of aspirin.

[1]

II.

Calculate the atom economy for aspirin as the desired product.

[1]

C

Evaluate the statement: "This synthesis is efficient because the percentage yield is high."

[2]

Question 44

HL • Paper 2

Hard

Calculator Permitted

HL • Paper 2

Hard

Calculator Permitted

Sulfur dioxide and oxygen react to form sulfur trioxide in the Contact process:

$2SO_2(g) + O_2(g) \to 2SO_3(g)$

A reactor is charged with $150\ \text{dm}^3$ sulfur dioxide and $90.0\ \text{dm}^3$ oxygen at the same temperature and pressure. The gases behave ideally for the purpose of this stoichiometric calculation. For part (b), the actual yield of sulfur trioxide is $85.0\%$ of the theoretical yield.

A

The reacting gas volumes may be compared using the coefficients in the equation.

I.

Identify the limiting reactant.

[2]

II.

Calculate the theoretical volume of sulfur trioxide formed.

[1]

B

The actual yield of sulfur trioxide is $85.0\%$ of the theoretical yield.

I.

Calculate the actual volume of sulfur trioxide formed.

[1]

II.

Calculate the volumes of sulfur dioxide and oxygen remaining, assuming no other reaction occurs.

[1]

C

Explain why increasing the percentage yield is not the same as improving atom economy for this reaction.

[2]

Question 45

HL • Paper 2

Hard

Calculator Permitted

HL • Paper 2

Hard

Calculator Permitted

Phosphate ions can be removed from wastewater by precipitation with aluminium ions:

$Al^{3+}(aq) + PO_4^{3-}(aq) \to AlPO_4(s)$

A treatment trial mixes $250.0\ \text{cm}^3$ of $0.0180\ \text{mol dm}^{-3}$ aluminium sulfate, $Al_2(SO_4)_3(aq)$ , with $500.0\ \text{cm}^3$ of $0.0120\ \text{mol dm}^{-3}$ sodium phosphate, $Na_3PO_4(aq)$ .

Solution	Formula	Volume / cm $^3$	Concentration / mol dm $^{-3}$
aluminium sulfate solution	$Al_2(SO_4)_3(aq)$	250.0	0.0180
sodium phosphate solution	$Na_3PO_4(aq)$	500.0	0.0120

A

The formulae of the soluble salts must be considered before applying the precipitation equation.

I.

Calculate the initial amounts, in mol, of $Al^{3+}$ ions and $PO_4^{3-}$ ions.

[2]

II.

Identify the limiting ion and calculate the theoretical mass of aluminium phosphate formed.

[2]

B

Use the results from part (a) to answer the following.

I.

Calculate the theoretical mass of aluminium phosphate formed.

[1]

II.

Calculate the concentration of $Al^{3+}$ ions remaining in solution after precipitation, assuming volumes are additive and no other aluminium species form.

[1]

C

Discuss why adding a large excess of aluminium sulfate may not be the best treatment strategy, even if it removes more phosphate.

[2]

Question 46

HL • Paper 2

Hard

Calculator Permitted

HL • Paper 2

Hard

Calculator Permitted

A hydrated sample of iron(II) sulfate, $FeSO_4 \cdot xH_2O$ , is analysed gravimetrically. A $1.112\ \text{g}$ sample is dissolved in water and excess barium chloride solution is added. The sulfate ions are precipitated as barium sulfate, $BaSO_4$ . After filtering, washing and drying, the mass of $BaSO_4$ is $0.933\ \text{g}$ .

$Ba^{2+}(aq) + SO_4^{2-}(aq) \to BaSO_4(s)$

A flow diagram of the gravimetric analysis: hydrated iron(II) sulfate sample dissolves in water, barium chloride is added, barium sulfate precipitate forms, then filtration, washing and drying occur before weighing. Boxes are labelled with the process steps only; no calculated values are shown.

A

The mass of barium sulfate is used to find the amount of sulfate in the original sample.

I.

Calculate the amount, in mol, of barium sulfate formed.

[1]

II.

Determine the value of $x$ in $FeSO_4 \cdot xH_2O$ .

[3]

B

I.

Calculate the percentage by mass of water in FeSO $_{4}$ $\cdot$ xH $_{2}$ O based on the calculated x value.

[1]

II.

State one reason why barium chloride is added in excess.

[1]

C

The barium sulfate precipitate was not dried completely before weighing. Evaluate the effect on the calculated value of $x$ .

[2]

Question 47

HL • Paper 2

Hard

Calculator Permitted

HL • Paper 2

Hard

Calculator Permitted

Propene oxide, $C_3H_6O$ , is an important industrial chemical. Two simplified routes are shown.

Route A: $C_3H_6 + Cl_2 + Ca(OH)_2 \to C_3H_6O + CaCl_2 + H_2O$

Route B: $C_3H_6 + H_2O_2 \to C_3H_6O + H_2O$

Propene oxide is the desired product in both routes.

Species	M_r / g mol $^{-1}$	Route A coeff.	Route B coeff.	Role
$C_3H_6$	42.09	1	1	reactant
$Cl_2$	70.90	1	—	reactant
$Ca(OH)_2$	74.10	1	—	reactant
$H_2O_2$	34.02	—	1	reactant
$C_3H_6O$	58.08	1	1	desired product
$CaCl_2$	110.98	1	—	by-product
$H_2O$	18.02	1	1	by-product

A

The atom economy of each route is calculated from the balanced equation.

I.

Calculate the atom economy for Route A.

[2]

II.

Calculate the atom economy for Route B.

[2]

B

Assume each route produces exactly $1.00\ \text{tonne}$ of propene oxide.

I.

Calculate the theoretical mass of calcium chloride by-product from Route A.

[1]

II.

Calculate the theoretical mass of water by-product from Route B.

[1]

C

Evaluate which route is preferable from a green chemistry perspective.

[2]

Question 48

HL • Paper 2

Hard

Calculator Permitted

HL • Paper 2

Hard

Calculator Permitted

Limestone containing calcium carbonate and unreactive impurities is heated strongly. Calcium carbonate decomposes according to:

$CaCO_3(s) \to CaO(s) + CO_2(g)$

A $5.00\ \text{g}$ limestone sample leaves $3.02\ \text{g}$ solid residue after heating to constant mass. The calcium oxide formed is then reacted with water to form calcium hydroxide, which is neutralised by hydrochloric acid:

$CaO(s) + H_2O(l) \to Ca(OH)_2(aq)$

$Ca(OH)_2(aq) + 2HCl(aq) \to CaCl_2(aq) + 2H_2O(l)$

A reaction sequence diagram showing limestone heated in a crucible to give solid residue and carbon dioxide gas, followed by addition of water to the residue and titration/neutralisation with hydrochloric acid. Labels show the chemical processes but no calculated masses or volumes.

A

The loss in mass during heating is due to carbon dioxide leaving the sample.

I.

Calculate the amount, in mol, of carbon dioxide produced.

[1]

II.

Calculate the percentage by mass of calcium carbonate in the limestone.

[2]

III.

Calculate the theoretical mass of calcium oxide formed.

[1]

B

The calcium oxide formed is assumed to react completely with water.

I.

Calculate the volume of $1.80\ \text{mol dm}^{-3}$ hydrochloric acid required to neutralise all the calcium hydroxide formed.

[2]

C

In an actual titration, only $46.2\ \text{cm}^3$ of the hydrochloric acid was required. Evaluate two possible reasons for this difference from the theoretical volume.