Identification of Ions & Gases (Cambridge (CIE) O Level Chemistry): Exam Questions

Choose a gas from the following list to answer the questions below.

Each gas may be used once, more than once or not at all.

It polymerises to form a poly(alkene).

It is a noble gas.

It is the main component of air.

It is a very reactive non-metal.

It burns to form water as the only product.

Choose a gas from the following list to answer the questions below. Each gas may be used once, more than once or not at all.

ammonia    argon    chlorine   ethene    hydrogen   

carbon dioxide   nitrogen   carbon monoxide   oxygen

Which gas

i) Is a noble gas?

[1]

ii) Is an acidic oxide?

[1]

iii) Can be polymerised?

[1]

iv) Is the active component of air?

[1]

v) Is used in the treatment of water?

[1]

Complete the following table.

Table 1 shows the mass of ions present in a 100 cm³ sample of milk.                                                                           Table 1

Describe a test for chloride ions.

 test ..................................................

 positive result  ..................................................

Calcium reacts with cold water to form two products: 

• a colourless gas, P, which ‘pops’ with a lighted splint

• a weakly alkaline solution, Q, which turns milky when carbon dioxide is bubbled through it.

i) Name gas P. 

[1]

 ii) Name the weakly alkaline solution Q. 

[1]

This question is about ammonia and ammonium salts.

Ammonia is a gas at room temperature.

What is the test for ammonia gas?

Describe the positive result of this test.

test .......................................................................

result ....................................................................

Ammonia reacts with water to form ions.                                          

NH₃ + H₂O NH₄⁺ + OH^–

Describe what is seen when aqueous ammonia is added to aqueous copper(II) sulfate, until no further change is seen.

Barium sulfate is an insoluble salt.

Barium sulfate can be made from aqueous ammonium sulfate using a precipitation reaction.

Name a solution that can be added to aqueous ammonium sulfate to produce a precipitate of barium sulfate.

This question is about tests for ions.

Describe the test for a nitrate ion.

test ___________________________

result __________________________

Describe a test for iodide ions.

test ______________________________

observations ______________________

Copper reacts with concentrated nitric acid to form copper(II) nitrate.

Cu (s) + 4HNO₃ (aq) → Cu(NO₃)₂ (aq) + 2NO₂ (g) + 2H₂O (l)

State the meaning of (aq).

An excess of copper is added to 25.0 cm³ of 16.0 mol / dm³ HNO₃.

Use this information, together with the equation, to calculate the volume of NO₂ formed. The gas volume is measured at room temperature and pressure.

Show your working and state the units.

When heated, Cu(NO₃)₂ decomposes to form CuO, NO₂ and O₂.

Construct the symbol equation for this reaction.

To a small sample of Cu(NO₃)₂ (aq), a student adds aqueous ammonia drop by drop until it is in excess.

i) Describe what is observed.

[2]

ii) The student repeats the experiment but adds aqueous sodium hydroxide instead of aqueous ammonia. Describe what is observed.

[1]

This question is about ammonium compounds.

The table shows the names and formulae of some ammonium compounds. 

i) Complete the table by giving the missing information. 

[2]

ii) When ammonia reacts with nitric acid, ammonium nitrate is formed. 

Write a chemical equation for this reaction. 

[1]

When ammonium chloride is heated, it undergoes thermal decomposition to form two gaseous products. 

Describe the result of testing each product with damp universal indicator paper. 

[3]

The diagram shows the apparatus used to heat ammonium chloride. 

i) Suggest why the damp litmus paper is two different colours. 

[1]

ii) Explain what happens to the damp litmus paper as the ammonium chloride is heated. 

 [3]

Explain why a fine white powder formed on the inside of the neck of the conical flask in part (c). 

[1]

An investigation into how the rate of reaction is affected by temperature is completed using the apparatus shown.

The time taken for the magnesium to stop reacting is measured.

i) Describe a test for the gas produced, including the positive observation, during this reaction. 

[2]

ii) Give the balanced symbol equation for the reaction that occurs during the gas test. 

[2]

State and explain what would happen to the rate of reaction between magnesium and hydrochloric acid as the temperature increased. 

[4]

2.0 g of magnesium reacted with 25.0 cm³ of 1.0 mol / dm³ hydrochloric acid is reacted at room temperature and pressure.

 The chemical equation for this reaction is 

Mg + 2HCl → MgCl₂ + H₂ 

Calculate the volume of hydrogen gas that would be produced in this reaction. Give your answer in dm³. 

[6]

The student repeated the experiment but used a white powder, compound X, instead of magnesium.

A gas was produced during the reaction with hydrochloric acid. When the gas was bubbled through turned limewater, it turned cloudy.

The student carried out a flame test on compound X and a lilac flame was produced.

Give the formula of compound X. Explain your answer. 

[3]

Solutions A, B and C were analysed.

Tests were done on each substance.

Identify the two ions present in each of the solutions A, B, and C.

[3]

What is the purpose of adding dilute acid in the tests with barium chloride and silver nitrate?  

[1]

Suggest what would be seen if the acid was not added. 

[1]

Explain why nitric acid is used before using silver nitrate instead of hydrochloric acid or sulfuric acid. 

[3]

A student investigates the mass of dissolved salts in 50 cm³ of an unknown solution. The solution is thought to contain sodium chloride and sodium carbonate.

The tests and some of the observations from the student's investigation are in the following table.

 Describe how the student should perform the flame test and include the expected result.

Explain why hydrochloric acid and sulfuric acid should not be used in test 2. Use chemical equations, including state symbols, to support your answer.

Hydrochloric acid

Reaction equation ................................................................................

 Explanation ................................................................................

 Sulfuric acid

 Reaction equation ................................................................................

 Explanation ................................................................................ 

[5]

The original apparatus used by the student consisted of a thistle funnel containing excess nitric acid connected to a conical flask of the unknown solution. The conical flask was also directly connected to a gas syringe to measure the volume of gas produced during test 2.

 The student suggested that test 2 could be improved by including a second conical flask containing limewater before the gas syringe as shown. 

i) Explain one advantage and one disadvantage of the student's suggested apparatus instead of the original apparatus.

Advantage ............................................................

Disadvantage ............................................................

[4]

ii) Use the results of test 2 to calculate the mass of sodium carbonate present in the unknown solution. 

[2]

i) Give the ionic equation to show the formation of the white precipitate in test 3. 

[1]

ii) Use the results of test 4 to calculate the mass of sodium chloride present in the unknown solution. 

[3]

A mixture of two solid compounds D and E was analysed. Solid D was a zinc salt which is soluble in water. Solid E was an insoluble metal carbonate. The tests on the mixture and some of the observations are in the following table.

Test 1: About half of the mixture of D and E was placed in a test-tube. The mixture was heated.

Observations:  Green to black, condensation formed

The rest of the mixture of D and E was added to distilled water in a boiling tube. The contents of the tube were filtered. The filtrate and the residue were kept for the following tests.

Complete observations for the following tests that were carried out on the residue

i) Test 1: The residue was transferred from the filter paper in to a test-tube. About 3 cm³ of dilute sulphuric acid was added. The gas was tested with limewater. 

Observations: ..........................................................................................................

[2]

ii) Test 2:

The solution obtained in (c) was divided into two equal portions.

The first portion was added excess aqueous sodium hydroxide, a little at a time.

Observations: pale blue precipitate

To the second portion was added excess aqueous ammonia, a little at a time.

Observations:  ..........................................................................................................

[4]

Three tests were carried out on the filtrate. 

Complete the observations for each test.

The filtrate from (a) was divided into three approximately equal portions.

i) Test 1: To the first portion were added drops of aqueous sodium hydroxide, a little at a time with shaking.

Observations: ..........................................................................................................

[2]

Excess aqueous sodium hydroxide was added.

Observations:..................................................................................

[1]

ii) Test 2: To the second portion was added excess aqueous ammonia a little at a time.

Observations: ..........................................................................................................

[3]

Test 3 : To the third portion were added drops of dilute hydrochloric acid and aqueous barium chloride.

Observations: white precipitate 

What conclusions can you draw about the identity of solid D?

[2]

What conclusion can you draw about the identity of the cation in solid E?

[1]