5.2 Quantitative Analysis

1 mark

0.0625 moles of methane is burnt in air according to the following equation:

CH₄ + 2O₂ → CO₂ + 2H₂O

How many moles of oxygen are required for this combustion reaction?

☐	A	0.03125
☐	B	0.0625
☐	C	0.125
☐	D	0.25

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1 mark

Higher Only

The reaction is completed at room temperature and pressure.

Use the equation to determine the volume, in dm³, of methane is being burned?

$volume of gas = moles x 24$

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1 mark

Higher Only

During the same reaction as described in part b), what volume, in dm³, of carbon dioxide is produced?

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1 mark

Higher Only

Assuming that all the chemicals involved in the reaction are in the gaseous state, the balanced symbol equation is:

CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (g)

What is the total volume of gas produced when 2500 cm³ of methane is burned?

☐	A	2500 cm³
☐	B	5000 cm³
☐	C	7500 cm³
☐	D	1000 cm³

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2 marks

Higher Only

In an experiment, ammonia gas is made by heating a mixture of ammonium chloride and calcium hydroxide.

2NH₄Cl(s) + Ca(OH)₂(s) → CaCl₂(s) + 2NH₃(g) + 2H₂O(l)

10.0 g of ammonium chloride is added to an excess of calcium hydroxide.

Calculate the maximum volume of ammonia gas that could be formed.

(relative atomic mass H = 1.00, N = 14.0, O = 16.0 and Ca = 40.0; one mole of any gas occupies 24 dm³at room temperature and pressure)

volume = ........................................................................... dm³

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5 marks

Sodium hydroxide solution reacts with hydrochloric acid.

NaOH + HCl → NaCl + H₂O

25.0cm³of 0.100 mol dm^–3 sodium hydroxide, NaOH, solution is added to 35.0cm³of 0.0750 mol dm^–3dilute hydrochloric acid, HCl.

Use the information to determine which reagent is in excess.

(3)

ii)

To find the exact amount of dilute hydrochloric acid that reacts with 25.0 cm³of the sodium hydroxide solution, a titration is carried out. Figure 14 shows the results for the titrations.

	1st titration	2nd titration	3rd titration	4th titration
final burette reading/ cm³	37.60	36.20	39.15	38.40
initial burette reading/ cm³	1.80	0.00	3.95	2.10
volume of acid used/ cm³	35.80	36.20	35.20	36.30

Figure 14

In this titration, the accurate volumes of acid used that are within 0.20 cm³of each other are considered concordant volumes.

Use the concordant results to calculate the mean volume of hydrochloric acid required.

(1)

mean volume = ....................................................................... cm³

iii)

During the titration, the indicator used changed colour at the end point.

Which of the following shows an indicator with the colour change that would be seen in this titration?

		indicator	colour in alkali	colour at end point
☐	A	phenolphthalein	colourless	pink
☐	B	phenolphthalein	pink	yellow
☐	C	methyl orange	red	yellow
☐	D	methyl orange	yellow	orange

(1)

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4 marks

In another titration, 25.0 cm³of a different sodium hydroxide solution is titrated with 0.200 mol dm^–3 sulfuric acid, H₂SO₄.

2NaOH + H₂SO₄→ Na₂SO₄ + 2H₂O

24.80 cm³of acid are required to neutralise 25.0 cm³of the sodium hydroxide solution.

Calculate the concentration of the sodium hydroxide solution, NaOH, in mol dm⁻³.

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7a4 marks

A sample of solid potassium hydroxide contained soluble, unreactive impurities.
A student tried to find the mass of potassium hydroxide in the sample, using the following method.

step 1	measure the mass of the sample of impure potassium hydroxide
step 2	dissolve the sample in 250 cm³of water in a beaker
step 3	take a 25 cm³sample of the potassium hydroxide solution using a measuring cylinder and pour into a conical flask
step 4	add 3 drops of indicator to the solution
step 5	put the conical flask on a white tile
step 6	using a burette, add dilute sulfuric acid of known concentration drop by drop to the solution, while swirling the flask
step 7	continue adding the sulfuric acid until the colour of the solution changes
step 8	record the volume of sulfuric acid added
step 9	use this result to calculate the mass of pure potassium hydroxide in the sample.

Suggest three ways to improve this method to obtain a more accurate mass of pure potassium hydroxide.

(3)

ii)

The indicator used was phenolphthalein.
Which row shows the colour change that would be seen in this titration?

(1)

		colour at start	colour at end point
☐	A	yellow	orange
☐	B	orange	yellow
☐	C	pink	colourless
☐	D	colourless	pink

How did you do?

4 marks

Higher Only

Another student carried out the titration accurately.
12.15 cm³of dilute sulfuric acid with a concentration of 0.140 mol dm^–3 reacted completely with 25.00 cm³of potassium hydroxide solution.

H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O

Calculate the concentration of this potassium hydroxide solution.

concentration of potassium hydroxide solution = ...................................... mol dm^–3

How did you do?

3 marks

Higher Only

A different solution of potassium hydroxide had a concentration of 0.175 mol dm^–3.

This potassium hydroxide solution was made by dissolving 2.56 g of impure potassium hydroxide to form 250 cm³of solution.

Calculate the percentage by mass of potassium hydroxide in the impure potassium hydroxide.
(relative formula mass: KOH = 56.0)

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1 mark

Higher Only

A student carrying out a titration finds that a 25.0 cm³ solution of 0.500 mol dm^-3 hydrochloric acid neutralises 35.0 cm³ of sodium hydroxide.

The balanced symbol equation for the reaction is:

NaOH + HCl → NaCl + H₂O

What is the concentration of the sodium hydroxide?

☐	A	0.15 mol dm^-3
☐	B	0.36 mol dm^-3
☐	C	0.72 mol dm^-3
☐	D	1.00 mol dm^-3

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1 mark

Calcium carbonate decomposes on heating to form calcium oxide and carbon dioxide.

CaCO₃ (s) → CaO (s) + CO₂ (g)

8.000 g of CaCO₃ was heated strongly for about 10 minutes. 6.213 g of solid remained.

Calculate the mass of carbon dioxide gas given off.

mass of carbon dioxide = .......................... g

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3 marks

A second sample of calcium carbonate is strongly heated in a crucible until there is no further loss in mass.

The mass of calcium oxide remaining in the crucible is 5.450 g.

The theoretical yield of calcium oxide in this experiment is 5.600 g.

Calculate the percentage yield of calcium oxide.

(2)

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

ii)

The mass of solid left in the crucible is less than the theoretical mass of calcium oxide that should be obtained.

A possible reason for this is that

(1)

☐	A	some solid was lost from the crucible
☐	B	the solid remaining absorbed some water from the air
☐	C	some carbon dioxide remained in the crucible
☐	D	the decomposition was incomplete

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6c3 marks

Another sample of calcium carbonate is heated and the mass of solid remaining is measured each minute.

The results are shown in Figure 11.

time in minutes	0	1	2	3	4	5	6	7
mass of solid remaining in g	9.0	8.1	7.2	6.4	6.0	5.6	5.3	5.2

Figure 11

Explain the trend shown by the data in Figure 11.

(2)

ii)

It is impossible to be sure from this data that the reaction is complete.

State why.

(1)

How did you do?

4 marks

Calculate the relative formula mass of calcium carbonate, CaCO₃.

(relative atomic masses: C = 12, O = 16, Ca = 40)

(2)

relative formula mass = .....................................

ii)

Calculate the atom economy for the formation of calcium oxide in this reaction.

CaCO₃ → CaO + CO₂

You must show your working.

(relative atomic masses: C = 12, O = 16, Ca = 40;

relative formula mass: calcium oxide = 56)

(2)

atom economy...............................

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9a2 marks

Potassium hydroxide reacts with hydrochloric acid to form potassium chloride and water.

potassium hydroxide + hydrochloric acid → potassium chloride + water

A student carried out a titration to find the exact volume of dilute hydrochloric acid that reacted with 25.0 cm³ of potassium hydroxide solution.

There were five steps in the titration.
The steps shown are not in the correct order.

step J	pour the potassium hydroxide solution into a conical flask and add a few drops of indicator to this solution
step K	fill a burette with the dilute hydrochloric acid and record the initial reading from the burette
step L	use a measuring cylinder to obtain 25 cm³ of potassium hydroxide solution
step M	take a final reading from the burette and calculate the volume of the dilute hydrochloric acid reacted
step N	run the dilute hydrochloric acid from the burette into the conical flask until the indicator changes colour

Write the steps in the correct order.

Some of the steps have been completed for you.

(1)

ii)

Suggest an alternative piece of apparatus that could be used in step L to obtain exactly 25.0 cm³ of potassium hydroxide solution.

(1)

How did you do?

9 marks

A student was then asked to produce a pure sample of solid potassium chloride.

After finding the volume of acid reacted in step M, the student added this volume of acid to a fresh 25.0 cm³ sample of the potassium hydroxide solution.
This mixture was then evaporated.

Explain why this new mixture was evaporated rather than the original mixture from the titration, to produce a pure sample of solid potassium chloride.

(2)

ii)

After evaporation, the mass of the potassium chloride was determined.

The theoretical yield of the experiment was 0.70 g.

The actual yield was 0.84 g.

This gave a percentage yield greater than 100%.

Calculate the percentage yield of this experiment.

(2)

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

iii)

Suggest a reason why the actual yield was greater than the theoretical yield.

(1)

iv)

The equation for the reaction between potassium hydroxide solution and dilute hydrochloric acid is

KOH + HCl → KCl + H₂O

Calculate the atom economy for the production of potassium chloride from potassium hydroxide and hydrochloric acid.

(relative formula masses: KOH = 56.0, HCl = 36.5, KCl = 74.5, H₂O = 18.0)
Give your answer to one decimal place.

(4)

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

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Final reading on the burette in cm³	29.20
Initial reading on the burette in cm³	1.60

Compound	Formula	Relative formula mass
Glucose	C₆H₁₂O₆	180
Ethene	C₂H₄
Ethanol	C₂H₅OH	46
Carbon dioxide	CO₂	44
Water	H₂O	18

1	a pipette is used to measure 25.00 cm³ of sodium hydroxide solution into a conical flask
2	a few drops of indicator are added to the sodium hydroxide solution
3	the burette is filled with hydrochloric acid
4	the hydrochloric acid is added to the sodium hydroxide solution until the indicator changes colour.

	titration
	rough	1	2
final burette reading in cm³	25.75	49.35	23.70
initial burette reading in cm³	0.00	25.75	0.00
volume of acid used in cm³	25.75	23.60	23.70

Edexcel GCSE Chemistry

Topic Questions

5.2 Quantitative Analysis

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☐	A	Potassium sulfate and hydrogen
☐	B	Potassium sulfate and water
☐	C	Potassium sulfide and hydrogen
☐	D	Potassium sulfide and water

☐	A	0.42 mol dm^-3
☐	B	0.105 mol dm^-3
☐	C	0.35 mol dm^-3
☐	D	0.21 mol dm^-3

☐	A	(NH)₄NO₃
☐	B	(NH₄NO)₃
☐	C	NH₄NO₃
☐	D	(NHNO)₁₂

☐	A	0.19 mol dm^-3
☐	B	0.23 mol dm^-3
☐	C	0.55 mol dm^-3
☐	D	0.82 mol dm^-3

		Atom economy	Percentage yield	Rate of reaction
☐	A	✔
☐	B	✔	✔
☐	C		✔	✔
☐	D	✔	✔	✔

☐	A	Burette, measuring cylinder, methyl orange
☐	B	Burette, measuring cylinder, universal indicator
☐	C	Burette, pipette, methyl orange
☐	D	Biuret, pipette, universal indicator

	titration 1	titration 2	titration 3	titration 4
final burette reading (cm³)	27	27.40	29.20	29.30
initial burette reading (cm³)	0	2.10	4.00	3.50
volume of acid used (cm³)	27	25.30	25.20	25.80

☐	A	The reaction is reversible
☐	B	Some ammonia is lost when separated from the reaction mixture
☐	C	Unreacted hydrogen and nitrogen are recycled
☐	D	Another side reaction occurred

☐	A	13.4 g
☐	B	15.0 g
☐	C	16.3 g
☐	D	12.4 g

☐	A	electrons
☐	B	neutrons
☐	C	protons
☐	D	nuclei

☐	A	60%
☐	B	70%
☐	C	75%
☐	D	80%

☐	A	7.0%
☐	B	25.6%
☐	C	74.4%
☐	D	93.0%