Tests for gases

This question is about gases.

The box gives the names of some gases.

Choose gases from the box to answer questions (i) to (iv).

You may use each gas once, more than once or not at all.

Identify two gases in Group 0 of the Periodic Table.

Identify the gas that makes up about 21% of the atmosphere.

Identify a greenhouse gas.

Identify the toxic gas formed by incomplete combustion of a hydrocarbon.

Describe a test to show that a gas is carbon dioxide.

This question is about a compound called potassium permanganate.

A teacher makes a saturated solution of potassium permanganate using this method.

The teacher adds 25 cm³ of water at 50 °C to a beaker.

The teacher then adds solid potassium permanganate one spatula at a time, while stirring, until the solution is saturated.

Give the meaning of the term saturated solution.

Give a reason why crystals form when the saturated solution cools from 50 °C to room temperature.

The teacher pours 25 cm³ of a saturated solution of potassium permanganate at room temperature into an evaporating dish.

The teacher leaves the solution until all the water has evaporated.

The teacher records the mass of the evaporating dish and the mass of the evaporating dish with the dry crystals.

mass of evaporating dish = 64.10 g

mass of evaporating dish with dry crystals = 65.35 g

Calculate the solubility of potassium permanganate in grams per 100 g of water.

[1.00 cm³ of water has a mass of 1.00 g]

solubility =_........ g per 100 g of water

The equation shows the thermal decomposition of potassium permanganate.

2KMnO₄ K₂MnO₄ + MnO₂ + O₂

Describe a test to show that oxygen gas is produced.

Calculate the M_r of K₂MnO₄

Potassium permanganate is an oxidising agent.

Give a reason why potassium permanganate is an oxidising agent.

The table gives some information about five gases.

Use gases from the table to answer these questions.

You may use each gas once, more than once or not at all.

Name the gas needed for combustion.

Name the gas that is most abundant in air.

Name the gas that can bleach damp litmus paper.

Explain why hydrogen chloride is classified as a compound.

Why does chlorine have the highest boiling point of the gases in the table?

Hydrogen peroxide decomposes to form water and oxygen.

This decomposition is shown in the equation.

Give the test for oxygen gas.

The rate of reaction is increased by adding a suitable catalyst.

Describe how a catalyst increases the rate of a reaction.

A student uses this apparatus to investigate the rate of decomposition of hydrogen peroxide solution.

The student adds 100 cm³ of hydrogen peroxide solution at 20 °C to the apparatus labelled A.

The student records the volume of oxygen gas collected every minute for 16 minutes.

The graph shows the student’s results.

Name the pieces of apparatus labelled A and B.

Determine the volume of oxygen gas produced in the first 4 minutes.

Show on the graph how you obtain your answer.

Determine the rate of reaction at 8 minutes by drawing a suitable tangent to the curve.

Include the units for the rate of reaction.

This question is about electrolysis.

This apparatus is used to collect the gases produced when an electric current passes through dilute sulfuric acid.

inert electrode inert electrode

Name a suitable material for the inert electrodes.

Give a test to show that the gas produced at the positive electrode is oxygen.

Give a test to show that the gas produced at the negative electrode is hydrogen.

Give an ionic half-equation for the formation of hydrogen at the negative electrode.

The oxygen gas in the tube has a volume of 17.8 cm³ at rtp.

Calculate the mass, in grams, of oxygen gas in the tube.

Give your answer to 3 significant figures.

[for O₂ at rtp, molar volume = 24 000 cm³]

This apparatus is used to electrolyse a concentrated solution of sodium chloride.

Give a reason why sodium chloride solution conducts electricity.

The positive ions in the solution are H⁺ and Na⁺.

Give a reason why hydrogen forms at the negative electrode rather than sodium.

A sample of the solution is taken from near the negative electrode. The sample is tested with universal indicator.

Explain the final colour of the universal indicator.

A student uses this apparatus to investigate the decomposition of hydrogen peroxide solution.

This is the equation for the reaction.

Give the test for oxygen.

Complete the dot‑and‑cross diagram for a molecule of hydrogen peroxide.

Show outer electrons only.

H O O H

The student measures the volume of oxygen collected at regular intervals until the reaction stops.

The table shows the student’s results.

Plot the student’s results on the grid.

Draw a curve of best fit.

Explain in terms of particle collision theory how decreasing the concentration affects the rate of a reaction.

The student repeats the experiment using the same volume of hydrogen peroxide solution but with half the original concentration.

All other conditions are kept the same.

On the grid, draw the curve you would expect the student to obtain.

In this reaction, the manganese(IV) oxide acts as a catalyst.

Explain how a catalyst works.

Sodium chloride is an ionic compound.

Explain why sodium chloride conducts electricity when it is molten or in solution, but not when it is solid.

A solution of sodium chloride can be electrolysed using this apparatus.

If the solution is dilute, a significant amount of oxygen collects at P.

Complete the ionic half-equation for this reaction.

If the solution is concentrated, chlorine is the main product that collects at P.

This is the ionic half-equation for the reaction.

State why this is an oxidation reaction.

The gas that collects at Q is hydrogen.

Give a test for hydrogen.

Explain how hydrogen gas forms at the negative electrode.

Hydrogen reacts with oxygen to form water.

The equation shows the covalent bonds in the molecules.

The table gives the bond energies.

Use the equation and the values in the table to calculate the enthalpy change, Δ H, for the reaction.

Include a sign in your answer.

Complete the diagram to show the energy levels of the reactants and products, and the enthalpy change, Δ H.

This question is about the reactions of iron.

Iron rusts when exposed to water and oxygen.

Give the chemical name of the compound that forms when iron rusts.

What type of reaction occurs when iron rusts?

Galvanising is a method used to prevent iron from rusting.

Give the name of the metal used to galvanise iron.

When iron reacts with dilute sulfuric acid, the products are iron(II) sulfate and hydrogen.

Give a chemical equation for the reaction between iron and sulfuric acid.

Give a test for hydrogen.

An excess of iron is added to copper(II) sulfate solution.

Name the type of reaction that occurs.

State the appearance of the solid that forms in the reaction.

Give the reason why no reaction occurs when iron is added to magnesium sulfate solution.

A teacher uses this apparatus to test the products of the combustion of liquid hydrocarbons.

Explain the change in appearance that occurs in the limewater.

The equation represents the complete combustion of an alkene.

C_nH_2n + oxygen carbon dioxide + nH₂O

Complete combustion of 0.0100 mol of the alkene produces 2.16 g of water.

Determine the molecular formula of this alkene.

[for H₂O, M_r = 18]

Give a reason why the mass of pure water that collects in the U-tube is less than 2.16 g.

Give a physical test to show that the water that collects in the U-tube is pure.

The teacher burns 30.0 g of heptane.

This is the equation for the complete combustion of heptane.

Calculate the minimum mass of oxygen needed for the complete combustion of 30.0 g of heptane.

[for C₇H₁₆, M_r = 100 for O₂, M_r = 32]

When copper(II) sulfate solution is electrolysed, copper forms at the negative electrode.

A student uses this apparatus to investigate the electrolysis of copper(II) sulfate solution.

Describe how the student could test a sample of copper(II) sulfate solution to show that it contains copper(II) ions.

Describe how copper metal forms at the negative electrode.

State the appearance of the copper that forms on the negative electrode.

Oxygen forms at the positive electrode.

Give a test for oxygen.

Complete the half-equation for the formation of oxygen at the positive electrode.

2H₂O _........ +_........ +_........

State why the formation of oxygen at the positive electrode is an oxidation reaction.

Describe the forces of attraction in metallic bonding.

When a small piece of potassium is added to water, bubbles of hydrogen gas are observed.

Give the test for hydrogen gas.

Give two other observations that would be made.

Explain why lithium is less reactive than potassium.

Refer to atomic structure in your answer.

This is the equation for the reaction between sodium and water.

A mass of 0.750 g of sodium is reacted with an excess of water.

Calculate the volume of hydrogen gas produced, in cm³, at room temperature.

[molar volume of hydrogen at rtp = 24 000 cm³]

[for Na,A_r = 23]

Give your answer to three significant figures.

This is the equation for the reaction between sodium hydroxide and sulfuric acid.

A volume of 25.0 cm³ of sodium hydroxide solution is completely neutralised by 16.3 cm³ of 0.0500 mol / dm³ sulfuric acid.

Calculate the concentration of the sodium hydroxide solution in mol / dm³.

concentration =_........ mol / dm

This question is about elements in Group 7 of the Periodic Table.

Which element is a liquid at room temperature?

What colour is solid iodine?

Describe a test for chlorine gas.

A sample of chlorine, containing two isotopes, has this percentage composition by mass.

chlorine‑35 71.2% chlorine‑37 28.8%

Calculate the relative atomic mass of this sample of chlorine.

Give your answer to one decimal place.

A student is given an aqueous solution of chlorine and an aqueous solution of sodium iodide.

Explain how the student can use these solutions to compare the reactivity of chlorine with the reactivity of iodine.

This question is about the oxides of some elements in Group 4 of the Periodic Table.

When 5.34 g of lead(II) carbonate are heated, lead(II) oxide and carbon dioxide are formed.

This is the equation for the reaction.

Give the name for this type of reaction.

Calculate the maximum mass of lead(II) oxide that can be formed from 5.34 g of lead(II) carbonate.

[for PbCO₃, M_r = 267 for PbO, M_r = 223]

The diagram shows apparatus used to heat lead(II) carbonate.

Complete the diagram to show what needs to be added to the apparatus to test that the gas released is carbon dioxide.

Give the result of the test.

Silicon dioxide (SiO₂) and carbon dioxide both contain covalent bonds.

Silicon dioxide is a solid with a high melting point. Carbon dioxide is a gas at room temperature.

Explain why silicon dioxide has a much higher melting point than carbon dioxide.

Refer to structure and bonding in your answer.

This question is about metal carbonates.

When heated, some metal carbonates decompose to form a metal oxide and carbon dioxide gas.

A student is given three solid metal carbonates, a timer, some limewater and this apparatus.

Describe a method the student can use to find out which metal carbonate decomposes fastest when heated.

A student is given a solid metal carbonate with the formula XCO₃

X represents the symbol of a Group 2 metal.

A student uses this apparatus to heat a sample of XCO₃ until it all decomposes.

The equation for the decomposition of XCO₃ is

The student records the mass of XCO₃ and the mass of carbon dioxide that escapes through the cotton wool plug.

These are the student’s results.

Give a reason why the student uses a cotton wool plug.

Calculate the amount, in mol, of carbon dioxide produced.

[for carbon dioxide M_r = 44]

Use the equation to determine the amount, in mol, of XCO₃ that decomposed.

Use the mass of XCO₃ and your answer to (b)(iii) to calculate the relative formula mass (M_r) of XCO₃

Use your answer to (b)(iv) and the Periodic Table on page 2 to determine the identity of the Group 2 metal X.

Show your working.

A student uses this apparatus to investigate the reaction between magnesium and dilute hydrochloric acid.

The word equation for the reaction is

magnesium + hydrochloric acid magnesium chloride + hydrogen

Complete the chemical equation for this reaction.

Give the test for hydrogen.

The student uses 0.090 g of magnesium and 0.025 mol of hydrochloric acid.

Show by calculation that the hydrochloric acid is in excess.

The student measures the volume of hydrogen collected at regular intervals until the reaction stops.

The table shows the student’s results.

Plot the student’s results.

Draw a curve of best fit.

Determine the volume of hydrogen collected in the first 10 seconds.

Show on the graph how you obtained your answer.

Explain why the rate of reaction is greatest at the start of the reaction.

The student repeats the experiment at a temperature 5 °C higher than the original temperature.

All other conditions are kept the same.

On the grid, draw the curve you would expect the student to obtain.

Explain, in terms of particle collision theory, how increasing the temperature affects the rate of reaction.

This question is about gases in the atmosphere.

The box gives the names of some gases.

Choose gases from the box to answer these questions.

Identify the least reactive gas in the atmosphere.

Identify the most abundant gas in the atmosphere.

Identify the gas that is not normally found in the atmosphere.

State an environmental problem caused by increasing amounts of carbon dioxide in the atmosphere.

Describe a test for carbon dioxide.

The diagram represents the structure of copper metal.

Explain three properties of copper that make it a suitable metal to use in electrical wiring.

The diagram shows the electrolysis of copper(II) sulfate solution, using graphite electrodes.

Copper forms at the negative electrode and oxygen forms at the positive electrode.

Give the formula of the copper ion and the formula of the sulfate ion in copper(II) sulfate.

copper ion

sulfate ion

State what would be seen at the positive electrode.

Give a test for oxygen.

Give an ionic half‑equation for the formation of oxygen at the positive electrode.

Suggest why the copper(II) sulfate solution contains some OH^– ions.

A student uses this apparatus to investigate the effect of heat on different solid metal carbonates.

This is the student’s method.

use a spatula to put some metal carbonate in the boiling tube

fit the delivery tube into position

pour some limewater into the test tube

start a timer and immediately begin to heat the metal carbonate

record the time when a change first occurs in the limewater

The student repeats the method using different metal carbonates.

When a metal carbonate is heated a reaction sometimes occurs.

The equation for the reaction is

metal carbonate metal oxide + carbon dioxide

State the name given to this type of reaction.

State two variables that the student should control in this investigation.

Suggest why bubbles appear in the limewater immediately after heating has started but before there is any change to the metal carbonate.

Explain the purpose of limewater in this investigation.

The table shows some of the results for the student’s investigation.

State the colour change that occurs for copper(II) carbonate.

Give a chemical equation for this reaction of copper(II) carbonate.

There is a relationship between the position of a metal in the reactivity series and how easily the metal carbonate reacts when heated.

Use the student’s results and your own knowledge to deduce this relationship.

State how you should extend the investigation to see if your deduction is correct.

Zinc reacts with dilute hydrochloric acid to form hydrogen.

Give a chemical equation for this reaction.

Give a test for hydrogen gas.

A student investigates the reaction between pieces of zinc and dilute hydrochloric acid.

In each experiment, he uses the same mass of zinc but a different volume of the acid.

He collects the hydrogen and measures its volume in each experiment.

The graph shows the student’s results.

Volume of dilute hydrochloric acid in cm³

Use the graph to find the minimum volume of acid needed to react with all of the zinc.

The student repeats the investigation, using hydrochloric acid of double the original concentration.

Determine the volume of hydrogen that would be collected using 15 cm³ of this acid.

Show your working on the graph.

Explain how increasing the concentration of the hydrochloric acid affects the rate of reaction.

The rate of reaction could also be affected by changing the temperature of the hydrochloric acid, or by using a catalyst.

Explain one other way in which the rate of reaction between zinc and hydrochloric acid can be affected.

This question is about gases.

The box gives the names of some gases.

Use gases from the box to answer these questions.

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

Name the most abundant gas in the Earth’s atmosphere.

Name the gas that is a compound.

Name the least reactive of the gases.

Name the gas formed by the complete combustion of hydrocarbons.

Describe the test for hydrogen gas.

This question is about ammonia gas, NH₃

Ammonia can be prepared in a laboratory from the reaction between ammonium chloride, NH₄Cl, and sodium hydroxide. The other products of the reaction are sodium chloride and water.

Give a chemical equation for this reaction.

Give a test for ammonia gas.

In industry, ammonia is produced from nitrogen and hydrogen.

The equation for this reaction is

In a sealed container, the reaction can reach a position of dynamic equilibrium.

Explain the meaning of the term dynamic equilibrium.

The graph shows the percentage yield of ammonia at equilibrium for different temperatures and pressures.

Using the graph, explain if the forward reaction is exothermic or endothermic.

(TOTAL FOR PAPER = 70 MARKS)

A solution of hydrogen peroxide decomposes when a catalyst of manganese(IV) oxide is added.

The products of the reaction are water and oxygen.

Complete the chemical equation for this reaction.

Give a test for oxygen.

State the reason for adding a catalyst.

A student investigates how changing the concentration of the hydrogen peroxide solution affects the rate of this reaction.

She uses this apparatus.

The student records the volume of oxygen that collects every 2 minutes for 16 minutes.

The table shows her results.

Plot the student’s results on the grid.

Draw a circle on the grid around the anomalous result.

Draw a curve of best fit through the points, ignoring the anomalous result.

Suggest a mistake that the student might have made to cause the anomalous result.

Determine the volume of oxygen collected during the first 3 minutes.

Show on your graph how you obtain your answer.

The student repeats the experiment using hydrogen peroxide solution of half the concentration of the original solution.

She keeps the volume of the hydrogen peroxide solution and all other conditions the same.

Draw on the grid the curve you would expect the student to obtain.

Explain how using hydrogen peroxide solution of half the concentration affects the rate of the reaction.

Refer to particle collision theory in your answer.

This question is about elements in Group 7 of the Periodic Table and their compounds.

Give the name of this group of elements.

State the colour of chlorine gas.

Give a test for chlorine gas.

Give a test to show that a solution contains iodide ions.

A student compares the reactivity of the elements bromine, chlorine and iodine.

He mixes these pairs of solutions and observes the reactions that occur.

• chlorine solution and potassium bromide solution

• bromine solution and potassium iodide solution

Explain how the reactions can be used to show the order of reactivity of the three elements.

Include the colour change that the student would observe in each reaction.

The table gives information about some lead compounds.

When a sample of red lead oxide is heated, it changes into a yellow solid and a gas forms that relights a glowing splint.

Complete the word equation for this reaction.

red lead oxide _........ +_........

A sample of one of the oxides of lead contains 86.6% lead and 13.4% oxygen by mass.

Show by calculation that the sample is lead(IV) oxide, PbO₂

[A_r of Pb = 207 A_r of O = 16]

Red lead oxide reacts with warm dilute nitric acid.

Complete the chemical equation for the reaction.

Pb₃O₄(_........ ) + 4HNO₃(_........ ) _........ Pb(NO₃)₂(aq) + PbO₂(s) +_........ H₂O(l)

A student is given a sample of solid red lead oxide and some dilute nitric acid.

Describe how the student could obtain a pure dry sample of lead(II) nitrate crystals.

A student is provided with a bottle containing a colourless solution X.

Solution X is thought to be dilute sulfuric acid of concentration 0.10 mol/dm³.

The student does some experiments on samples of solution X to try to show that it is dilute sulfuric acid.

The student adds a few drops of litmus to a sample of solution X.

The litmus turns red.

The student knows that the products of the electrolysis of dilute sulfuric acid are hydrogen and oxygen.

She carries out the electrolysis using this apparatus.

Suggest why the student does not use zinc electrodes in her experiment.

State what is observed at both the anode and the cathode during the electrolysis.

Which of these tests shows that the gas formed at the cathode is hydrogen?

Describe a test to show that solution X contains sulfate ions.

The student then does a titration to see if the concentration of the dilute sulfuric acid is 0.10 mol/dm³.

She measures 25.0 cm³ of potassium hydroxide solution into a conical flask, and then adds a few drops of indicator solution.

Name the piece of apparatus the student should use to measure 25.0 cm³ of the potassium hydroxide solution.

The concentration of potassium hydroxide in the solution is 0.125 mol/dm³.

Calculate the amount, in mol, of KOH in 25.0 cm³ of this solution.

The equation for the reaction in the titration is

Calculate the volume, in cm³, of 0.10 mol/dm³ sulfuric acid needed to neutralise 25.0 cm³ of the potassium hydroxide solution.

Carbon dioxide changes directly from a solid to a gas without becoming a liquid.

Give the name of the change of state from solid to gas.

Describe the test for carbon dioxide gas.

Carbon dioxide is a simple molecular covalent substance.

Explain why carbon dioxide turns from a solid to a gas at a very low temperature.

Diamond and graphite are both giant covalent substances made up of carbon atoms.

● diamonds are used in cutting tools

● graphite is used in pencils to make marks on paper

Explain, with reference to structure and bonding, why each substance is suitable for its particular use.

This question is about Group 1 metals and their reactions.

When lithium is added to water, bubbles of hydrogen gas are observed.

Give two other observations that could be made.

Give the test for hydrogen gas.

Give one observation that would be different if potassium is used instead of lithium.

The diagram represents an atom of lithium and an atom of potassium.

Explain why potassium is more reactive than lithium.

The equation for the reaction between lithium and water is

A mass of 0.500 g of lithium reacts with an excess of water.

Calculate the volume, in cm³, of hydrogen gas produced at rtp.

[molar volume of a gas at rtp = 24 000 cm³]

Give your answer to three significant figures.

In a reaction between lithium and water, 150 cm³ of lithium hydroxide solution is formed.

The lithium hydroxide solution is then completely neutralised by 24.85 cm³ of 0.100 mol/dm³ sulfuric acid.

The equation for the neutralisation is

Calculate the concentration, in mol/dm³, of the lithium hydroxide solution.

concentration =_........ mol/dm

Oxygen can be prepared from hydrogen peroxide using a catalyst.

Which is a correct statement about oxygen?

Explain how a catalyst increases the rate of a reaction.

The equation for the preparation of oxygen from hydrogen peroxide is

This equation can also be written using displayed formulae to show all the covalent bonds in the molecules.

The table gives the bond energies for these bonds.

Use the values in the table to calculate the enthalpy change, Δ H, for the reaction.

Include a sign in your answer.

Complete the energy level diagram to show the position of the products and the enthalpy change, Δ H, for the reaction.

This question is about gases in the atmosphere.

The box gives the names of some gases in the atmosphere.

Use gases from the box to answer the questions.

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

Identify the two noble gases.

Identify the gas that is a compound.

Identify the most abundant gas in the atmosphere.

Identify the greenhouse gas.

Describe the test for oxygen.