Groups 1 & 2 (Edexcel A Level Chemistry): Exam Questions

This question is about flame tests for Group 1 and 2 metal ions.

i) State the colour of the flame produced by separate samples of potassium and strontium ions.

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Potassium ions .................................................................................................. Strontium ions....................................................................................................

ii) Give a reason why carrying out a flame test on a mixture of potassium chloride and strontium chloride does not clearly show that two different metal ions are present.

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In the first stage of the flame test, the nichrome wire is dipped into concentrated hydrochloric acid and then heated in a Bunsen flame.

In the second stage, this nichrome wire is dipped into fresh hydrochloric acid and then into the metal salt to be tested before being reheated in the Bunsen flame.

i) Give two reasons why the wire is made of nichrome and not iron.

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ii) Give a reason why the wire is dipped into acid and then heated in the first stage.

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iii) State why fresh concentrated hydrochloric acid is used in the second stage of the flame test.

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iv) State why hydrochloric acid is used in the second stage of the flame test.

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Explain, with reference to electron transitions, the formation of the colour in a flame test.

Thermal decomposition is the breaking down of a substance by heat.  

An experiment was carried out to investigate the thermal decomposition of a metal nitrate using the apparatus shown. 

i) The glowing splint is used as a test for one of the gases given off in this experiment. Identify this gas and the positive result of the test.

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ii) Give the name and appearance of the other gas given off in this experiment when a Group 2 nitrate is heated.

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iii) Write the equation for the decomposition if the Group 1 compound, sodium nitrate, was used in this experiment. State symbols are not required.

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iv) Describe the apparatus that would be used to compare the decomposition of metal carbonates. Include how the rate of decomposition would be compared.

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Explain why magnesium carbonate decomposes much more readily on heating than barium carbonate.

A solid, white, water-soluble compound was thought to be magnesium bromide. A student carried out tests to confirm the identity of both ions present.

A flame test was carried out to test for the cation.

i) Describe how a flame test is carried out.

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ii) Explain the origin of flame test colours.

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iii) Give a reason why the magnesium ion does not produce a flame colour.

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iv) Give a reason why the lack of a flame colour is not a positive test for the magnesium ion.

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i) Give the formula of a reagent that would produce a cream-coloured precipitate when added to an aqueous solution of magnesium bromide.

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ii) The identity of the anion may be confirmed by testing the solubility of the cream-coloured precipitate in ammonia solution. Which pair of responses helps to confirm the identity of the anion?

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The nitrates of lithium, rubidium and strontium are all white solids. The compounds are held together by ionic bonds.

State the meaning of the term ‘ionic bond’.

What is the percentage by mass of strontium in strontium nitrate?

These three compounds cannot be identified with certainty from a flame test as the colours seen are similar. Concentrated hydrochloric acid is used in a flame test procedure.

i) Which of the following is a reason for dipping the flame test wire in concentrated hydrochloric acid during a flame test procedure?

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ii) The flame colour given by these three solids in the flame test are shades of

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iii) What is the best explanation for why metal ions produce different flame colours?

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Different wavelengths of light energy are

Devise a procedure to identify the nitrates of lithium, rubidium and strontium using the effect of heat on the three solids and any precipitation reactions of the compounds.

Practical details are not required, but you should give the observations expected in each case.

This question is about the thermal stability of Group 1 and Group 2 nitrates and carbonates.

Complete the equations for the thermal decomposition of sodium nitrate, NaNO₃ , and for the thermal decomposition of calcium nitrate, Ca(NO₃)₂ .

State symbols are not required.

NaNO₃ →

Ca(NO₃)₂ →

The thermal stability of Group 1 nitrates increases down the group.

The decomposition temperatures of some Group 1 nitrates are shown.

Explain why the thermal stability of caesium nitrate is greater than that of sodium nitrate.

Calcium carbonate is thermally decomposed during the manufacture of cement.

i) Write an equation, including state symbols, for the thermal decomposition of calcium carbonate.

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ii) Name all the types of bond present in calcium carbonate.

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iii) Give a reason, in terms of the bonding, why a high decomposition temperature is required.

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