Groups 1 & 2 (Edexcel International A Level Chemistry)

Exam Questions

33 mins7 questions
1a5 marks

This question is about Group 1 metals.

When potassium is placed into a beaker of cold water, potassium hydroxide and hydrogen are formed.

i)
Write the equation for this reaction. Include state symbols.

(2)

ii)

This is a redox reaction.

State which element is oxidised and which is reduced.
Justify your answer by giving the initial and final oxidation numbers of any element that changes oxidation state.

(2)

iii)
The reaction of potassium with water is very vigorous and a flame is seen.

State the colour of the flame.

(1)

1b
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6 marks

The label has come off a bottle known to contain M, a Group 1 metal which is stored in oil.
A student carried out an experiment to determine the identity of M.

Procedure

Step 1 A small piece of M was wiped with tissue paper to remove the oil.
The piece of M was weighed and placed in a beaker of distilled water.
Step 2

After the reaction had finished, the contents of the beaker and washings were transferred to a 250.0 cm3 volumetric flask. The solution was made up to the mark with distilled water and mixed thoroughly.

Step 3

A pipette was used to transfer 25.0 cm3 portions of this solution to conical flasks. Each portion was then titrated with hydrochloric acid of concentration 0.400 mol dm–3.

Results

Mass of metal, M 0.37 g
Mean titre of hydrochloric acid 12.80 cm3


The reaction taking place is shown.

MOH (aq) + HCl (aq) → MCl (aq) + H2O (l)

i)
The indicator used was phenolphthalein.
State the colour change at the end-point.

(2)


from ........................................... to ......................................

ii)
Calculate the relative atomic mass of M and use it to identify the Group 1 metal, M.

(4)

1c
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2 marks

Another student repeated the experiment, using a different sample of metal M, but did not wipe off the oil before weighing it.

State how this would change the calculated value of the relative atomic mass of M. Justify your answer.

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2a
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4 marks

Magnesium oxalate, MgC2O4, decomposes on heating to form magnesium carbonate and carbon monoxide.

MgC2O4 (s) → MgCO3 (s) + CO (g)

A 6.0 g sample of magnesium oxalate was heated for three minutes but the decomposition was only 70% complete.

Calculate the total mass of solid that remains.

2b3 marks

In practice, magnesium carbonate also decomposes on stronger heating.

Describe and explain the trend in the thermal decomposition of Group 2 carbonates.

2c1 mark

Suggest why a pure sample of magnesium carbonate will not be produced from the decomposition of magnesium oxalate even if the sample is heated for longer.

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3a
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5 marks

Magnesium ethanedioate (MgC2O4) decomposes on gentle heating to form magnesium carbonate and carbon monoxide.

MgC2O4 → MgCO3 + CO

i)
State why the thermal decomposition of magnesium ethanedioate should be carried out in a fume cupboard.

(1)

ii)

After heating a 6.0 g sample of magnesium ethanedioate for three minutes, the decomposition was 70% complete.

Calculate the total mass of the solid mixture that remains.

(4)

3b
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3 marks

Magnesium carbonate undergoes thermal decomposition at a higher temperature than magnesium ethanedioate.

MgCO3 → MgO + CO2

Explain the trend in the thermal decomposition of Group 2 carbonates going down the group.

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