Quantitative Analysis Practice Questions

Question 1

4 marks

This question is about the concentration of solutions.

(relative formula masses: $\mathrm{Na_2CO_3} = 106$ , $\mathrm{KOH} = 56$ )

(a)

A student dissolved $5.30\ \mathrm{g}$ of anhydrous sodium carbonate, $\mathrm{Na_2CO_3}$ , in distilled water and made the solution up to $500\ \mathrm{cm^3}$ in a volumetric flask.

Calculate the concentration of this solution in $\mathrm{mol\ dm^{-3}}$ .

concentration = ............................................................... $\mathrm{mol\ dm^{-3}}$

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(b)

A solution of potassium hydroxide has a concentration of $0.250\ \mathrm{mol\ dm^{-3}}$ .

Calculate the concentration of this solution in $\mathrm{g\ dm^{-3}}$ .

concentration = ............................................................... $\mathrm{g\ dm^{-3}}$

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Question 2

4 marks

The molar volume of any gas at room temperature and pressure (rtp) is $24\ \mathrm{dm^3}$ ( $24\,000\ \mathrm{cm^3}$ ).

(a)

Calculate the volume, in $\mathrm{dm^3}$ , occupied by $0.35\ \mathrm{mol}$ of oxygen gas at rtp.

volume = ............................................................... $\mathrm{dm^3}$

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(b)

A balloon contains $720\ \mathrm{cm^3}$ of helium gas at rtp.

Calculate the number of moles of helium in the balloon.

number of moles = ............................................................... $\mathrm{mol}$

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Question 3

3 marks

A student titrated $25.0\ \mathrm{cm^3}$ of sodium hydroxide solution with dilute hydrochloric acid, using methyl orange as the indicator. The sodium hydroxide solution was in the conical flask and the acid was added from a burette.

(a)

Name the piece of apparatus the student should use to measure out exactly $25.0\ \mathrm{cm^3}$ of the sodium hydroxide solution into the conical flask.

/ 1

(b)

Which row shows the colour change of the indicator that the student would see at the end point of this titration?

A red → yellow
B yellow → red
C colourless → pink
D pink → colourless

/ 1

(c)

Give a reason why the conical flask is placed on a white tile during the titration.

/ 1

Question 0

7 marks

A student used titration to find the concentration of ethanoic acid in a sample of diluted vinegar.

She pipetted $25.0\ \mathrm{cm^3}$ of the diluted vinegar into a conical flask and titrated it with sodium hydroxide solution of concentration $0.200\ \mathrm{mol\ dm^{-3}}$ .

Her results are shown in the table.

Titration	rough	1	2	3
Volume of sodium hydroxide added / cm $^3$	22.30	21.55	21.85	21.45

The equation for the reaction is

$\mathrm{CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O}$

(a)

Identify the concordant results and use them to calculate the mean titre.

mean titre = ............................................................... $\mathrm{cm^3}$

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(b)

Calculate the concentration, in $\mathrm{mol\ dm^{-3}}$ , of the ethanoic acid in the diluted vinegar.

concentration = ............................................................... $\mathrm{mol\ dm^{-3}}$

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(c)

Convert the concentration of the ethanoic acid into $\mathrm{g\ dm^{-3}}$ .

(relative formula mass: $\mathrm{CH_3COOH} = 60$ )

concentration = ............................................................... $\mathrm{g\ dm^{-3}}$

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Question 0

7 marks

Magnesium ribbon burns in oxygen to form magnesium oxide.

$\mathrm{2Mg + O_2 \rightarrow 2MgO}$

A student heated $4.80\ \mathrm{g}$ of magnesium ribbon in a crucible until it had all burned. The mass of magnesium oxide obtained was $7.20\ \mathrm{g}$ .

(relative atomic mass: $\mathrm{Mg} = 24$ ; relative formula mass: $\mathrm{MgO} = 40$ )

(a)

Calculate the theoretical yield of magnesium oxide, in g.

theoretical yield = ............................................................... $\mathrm{g}$

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(b)

Calculate the percentage yield of magnesium oxide in this experiment.

percentage yield = ............................................................... %

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(c)

Suggest two reasons why the actual yield of magnesium oxide was less than the theoretical yield.

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Question 0

5 marks

Iron is extracted from iron(III) oxide in a blast furnace. One of the reactions that takes place is

$\mathrm{Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2}$

(relative atomic masses: $\mathrm{C} = 12$ , $\mathrm{O} = 16$ , $\mathrm{Fe} = 56$ )

(a)

State what is meant by the atom economy of a reaction.

/ 1

(b)

Calculate the atom economy of this reaction for producing iron.

atom economy = ............................................................... %

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(c)

Give one reason why a company wants the reactions it uses to have a high atom economy.

/ 1

Question 0

5 marks

Carbon monoxide burns in oxygen to form carbon dioxide.

$\mathrm{2CO(g) + O_2(g) \rightarrow 2CO_2(g)}$

In parts (a) and (b), all gas volumes are measured at the same temperature and pressure.

(a)

Calculate the volume of oxygen needed to react completely with $80\ \mathrm{cm^3}$ of carbon monoxide.

volume of oxygen = ............................................................... $\mathrm{cm^3}$

/ 1

(b)

State the volume of carbon dioxide formed when $80\ \mathrm{cm^3}$ of carbon monoxide reacts completely.

volume of carbon dioxide = ............................................................... $\mathrm{cm^3}$

/ 1

(c)

A separate sample of carbon dioxide has a volume of $240\ \mathrm{cm^3}$ at room temperature and pressure.

Calculate the mass of this sample.

(molar volume at rtp $= 24\,000\ \mathrm{cm^3}$ ; relative formula mass: $\mathrm{CO_2} = 44$ )

mass = ............................................................... $\mathrm{g}$

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Question 0

7 marks

Sodium hydrogencarbonate decomposes when it is heated.

$\mathrm{2NaHCO_3 \rightarrow Na_2CO_3 + H_2O + CO_2}$

(relative formula mass: $\mathrm{NaHCO_3} = 84$ ; molar volume at rtp $= 24\ \mathrm{dm^3}$ )

(a)

A sample of $8.40\ \mathrm{g}$ of sodium hydrogencarbonate was heated until there was no further change in mass.

Calculate the volume of carbon dioxide, in $\mathrm{dm^3}$ , produced at rtp.

volume of carbon dioxide = ............................................................... $\mathrm{dm^3}$

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(b)

In a different experiment, $0.360\ \mathrm{dm^3}$ of carbon dioxide, measured at rtp, was collected.

Calculate the mass of sodium hydrogencarbonate that decomposed.

mass = ............................................................... $\mathrm{g}$

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Question 0

5 marks

A student was asked to find the concentration of a dilute solution of sulfuric acid by titrating it against sodium carbonate solution of known concentration.

The student used this method.

step 1 rinse the burette with distilled water, then fill it with the dilute sulfuric acid
step 2 use a measuring cylinder to transfer $25\ \mathrm{cm^3}$ of $0.100\ \mathrm{mol\ dm^{-3}}$ sodium carbonate solution into a conical flask
step 3 add a few drops of methyl orange indicator
step 4 run acid into the flask quickly until the solution turns red
step 5 record the volume of acid added, then repeat the titration once more

(a)

Suggest three improvements to this method that would give a more accurate value for the concentration of the sulfuric acid.

/ 3

(b)

Explain the effect on the titre of filling the burette while it is still wet with distilled water.

/ 2

Question 0

6 marks

A solution of sodium hydroxide has a concentration of $8.00\ \mathrm{g\ dm^{-3}}$ .

It is neutralised by dilute sulfuric acid of concentration $0.125\ \mathrm{mol\ dm^{-3}}$ , added from a burette.

$\mathrm{2NaOH + H_2SO_4 \rightarrow Na_2SO_4 + 2H_2O}$

(relative formula mass: $\mathrm{NaOH} = 40$ )

(a)

Calculate the volume of the dilute sulfuric acid needed to neutralise exactly $25.0\ \mathrm{cm^3}$ of this sodium hydroxide solution.

volume = ............................................................... $\mathrm{cm^3}$

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(b)

The titration was repeated with $25.0\ \mathrm{cm^3}$ of the same sodium hydroxide solution, but using sulfuric acid that had been diluted by mixing it with an equal volume of distilled water.

Deduce the volume of the diluted acid needed and explain your answer.

volume = ............................................................... $\mathrm{cm^3}$

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Question 0

7 marks

Ethanol can be manufactured by two different routes.

Route A — hydration of ethene

$\mathrm{C_2H_4 + H_2O \rightarrow C_2H_5OH}$

	Route A
Conditions	$300\ ^\circ\mathrm{C}$ , $60$ atm, catalyst
Rate of reaction	fast, continuous process
Position of equilibrium	reversible; only about 5 % converted each pass, but unreacted gases are recycled giving an overall yield of about 95 %
Raw material	ethene, obtained from crude oil

Route B — fermentation of glucose

$\mathrm{C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2}$

	Route B
Conditions	$30\ ^\circ\mathrm{C}$ , yeast
Rate of reaction	slow, takes several days; batch process
Yield	about 85 %
Raw material	glucose from sugar cane or sugar beet

(relative formula masses: $\mathrm{C_6H_{12}O_6} = 180$ , $\mathrm{C_2H_5OH} = 46$ )

(a)

Calculate the atom economy of Route B for producing ethanol.

atom economy = ............................................................... %

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(b)

The atom economy of Route A is 100 %. Explain why.

/ 1

(c)

A company must choose one of these routes to manufacture ethanol.

Using the information given, evaluate the two routes and justify which one the company should choose.

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Question 0

6 marks

A sample of washing soda contained sodium carbonate together with impurities that do not react with acids.

A student weighed out $1.30\ \mathrm{g}$ of the sample, dissolved it in distilled water and made the solution up to $250\ \mathrm{cm^3}$ in a volumetric flask.

$25.0\ \mathrm{cm^3}$ portions of this solution were titrated with hydrochloric acid of concentration $0.100\ \mathrm{mol\ dm^{-3}}$ . The mean titre was $22.40\ \mathrm{cm^3}$ .

$\mathrm{Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2}$

(relative formula mass: $\mathrm{Na_2CO_3} = 106$ )

(a)

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

percentage by mass = ............................................................... %

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(b)

During one titration, a few drops of the solution splashed out of the conical flask before the end point was reached.

Explain the effect this would have on the value calculated for the percentage by mass of sodium carbonate.

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Atomic Structure

States of Matter & Mixtures

Chemical changes

Extracting metals & equilibria

Separate Chemistry 1

Groups in the periodic table

Rates of reaction & energy changes

Fuels & Earth science

Separate Chemistry 2

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