Relative formula mass

Calcium phosphate is an ionic compound with the formula Ca₃(PO₄)₂

What is the total number of atoms in the formula Ca₃(PO₄)₂?

What are the correct charges on the ions in calcium phosphate?

Calculate the relative formula mass (M_r) of Ca₃(PO₄)₂

M_r of Ca₃(PO₄)₂ =_........

Calculate the percentage by mass of calcium in calcium phosphate.

Calcium hydroxide can react with phosphoric acid to form calcium phosphate.

Complete the equation for this reaction.

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.

Diamond and graphite are both forms of the element carbon.

Diamond and graphite both have covalent bonds and giant covalent structures.

The diagram represents the structure of diamond and the structure of graphite.

Give a reason why diamond is an element.

Describe the forces of attraction in a covalent bond.

Explain why graphite conducts electricity.

Explain why diamond is hard but graphite is soft.

Another form of carbon has molecules with the formula C_x

x represents the number of carbon atoms in each molecule.

Each molecule of C_x has a mass of 1.40 × 10⁻²¹ g.

One mole of C_x contains 6.02 × 10²³ molecules.

Calculate the M_r of C_x and the value of x

[for carbon, A_r = 12]

This question is about sulfur.

The diagram represents the electronic configuration of an atom of sulfur.

Which period of the Periodic Table contains sulfur?

What is the charge on a sulfide ion?

When a mixture of sulfur and zinc is heated to a high temperature a reaction occurs, forming the compound zinc sulfide, ZnS

Give a reason why the mixture of sulfur and zinc needs heating before a reaction occurs.

Calculate the relative formula mass (M_r) of zinc sulfide.

[for Zn, A_r = 65 for S, A_r = 32]

This question is about gases.

The table gives information about five gases.

Use information from the table to answer these questions. Each gas may be used once, more than once or not at all.

Give the name of the gas that is about 79 % of the atmosphere by volume.

Give the name of the gas that is a compound.

Give the name of the least reactive gas.

Give the name of the gas that is not normally found in the atmosphere.

Give the name of the gas that affects global warming.

Calculate the M_r for carbon dioxide.

Give a reason why it is not possible to give information for air in the table.

When copper(II) carbonate is heated, the products are copper(II) oxide and carbon dioxide.

Give the name for this type of reaction.

Give the colour change that occurs during this reaction.

Give a chemical equation for this reaction.

When solutions of lead(II) nitrate and potassium chloride are mixed, a precipitate of lead(II) chloride forms.

Complete the equation for the reaction by adding the state symbols.

Give the formula of each ion in lead(II) nitrate.

lead ion

nitrate ion

Calculate the relative formula mass (M_r) of lead(II) nitrate, Pb(NO₃)₂

A student investigates the height of the precipitate formed when lead(II) nitrate solution is added to potassium chloride solution.

This is the student’s method.

Step 1&$pour=NRKM cm³ of potassium chloride solution into a boiling tube

Step 2&$~dd=OKM cm³ of lead(II) nitrate solution and allow the precipitate to settle

Step 3 measure the height of the precipitate

Repeat steps 2 and 3 until a total of 14.0 cm³ of lead(II) nitrate solution has been added.

The table shows the student’s results.

Plot the results on the grid.

Draw a circle around the anomalous result.

Draw a line of best fit through the first four points and another line of best fit through the last three points. Make sure that the lines cross.

Volume of lead(II) nitrate in cm³

Give two possible mistakes the student could have made to cause the anomalous result.

State why the first line of best fit should pass through the origin.

Use your graph to determine the volume of lead(II) nitrate solution needed to react completely with 15.0 cm³ of potassium chloride solution.

This question is about organic compounds.

Give the total number of atoms in one molecule of methanoic acid.

Determine the relative molecular mass (M_r) of methanoic acid.

Explain why methanoic acid is not a hydrocarbon.

The atoms in methanoic acid are held together by covalent bonds.

State, in terms of electrostatic attractions, what is meant by the term covalent bond.

Draw a dot‑and‑cross diagram to show the bonding in a molecule of methanoic acid.

Show only the outer electrons of each atom.

Calculate the empirical formula of the organic compound with this composition by mass.

C = 52.2% H = 13.0% O = 34.8%

This question is about polymers.

This is the structure of a monomer.

What is the name of this monomer?

Complete the equation to show the repeat unit of the polymer that forms from this monomer.

A typical molecule of the polymer has a relative molecular mass (M_r) of 2 490 000

Show that the number of monomer molecules needed to make this typical molecule is about 40 000

[for C, A_r = 12 for Cl, A_r = 35.5]

These are two methods used to dispose of the polymer.

• burying in landfill sites

• burning

Discuss the environmental problems caused by these two methods of disposal.

A different polymer molecule contains 10 600 atoms of carbon, 10 600 atoms of hydrogen and 31 800 atoms of chlorine.

Determine the empirical formula of this polymer.

This question is about ionic compounds.

The table gives the formulae of some positive and negative ions, and the formulae of some compounds containing these ions.

Complete the table by giving the missing formulae.

Give the name of the compound with the formula MgO

Calculate the relative formula mass (M_r) of Na₃N

[for Na, A_r = 23 for N, A_r = 14]

The diagram shows the arrangement of electrons in atoms of lithium and in an atom of oxygen.

Describe the changes in the electron configurations of lithium and oxygen when these atoms form lithium oxide, Li₂O

Lithium oxide has a giant ionic structure.

Explain why lithium oxide has a high melting point.

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.

This question is about alkanes and alkenes.

The alkane C₅H₁₂ has three isomers.

State what is meant by the term isomers.

Calculate the relative formula mass (M_r) of C₅H₁₂

This is the displayed formula of one of the isomers.

H H H H H

Give the name of this isomer.

Draw the displayed formulae of the other two isomers.

Isomer 1
Isomer 2

Ethane (C₂H₆) and ethene (C₂H₄) both react with bromine.

Describe the differences in the reactions of ethane and ethene with bromine.

Refer to the conditions, the products and the types of reaction involved.

A potassium permanganate crystal is placed in a beaker of water.

After several days a coloured solution forms.

Give the names of the two processes that cause the coloured solution to form.

The formula of potassium permanganate is KMnO₄

How many different types of atom are in KMnO₄?

Calculate the relative formula mass (M_r) of KMnO₄

Potassium permanganate can be used as an oxidising agent.

State what is meant by the term oxidising agent.

This question is about sodium oxide, Na₂O

The diagram shows the electronic configuration of atoms of sodium and oxygen.

Describe the changes in the electronic configuration of the atoms of sodium and oxygen to form the ions in sodium oxide.

Calculate the relative formula mass (M_r) of sodium oxide, Na₂O, using information from the Periodic Table.

Explain why solid sodium oxide does not conduct electricity.

Give a test to show that sodium oxide contains sodium ions.

When sodium oxide is heated it reacts to form sodium metal and sodium peroxide, Na₂O₂

Complete the equation for this reaction.

Crude oil is a mixture of hydrocarbons.

This passage is about the industrial separation of crude oil.

Complete the passage by adding the missing words.

Crude oil is_........ to form vapour.

The vapour is passed through a_........ column.

The refinery gases are collected at the top of the column because they have low

Bitumen is collected at the bottom of the column.

Give one use of bitumen.

One of the hydrocarbons in crude oil is an alkane with this structural formula.

Give the name of this alkane.

Calculate the relative molecular mass (M_r) of this alkane.

Catalytic cracking is used to convert long-chain alkanes into shorter-chain alkanes.

Give the name of the catalyst and the temperature used in catalytic cracking.

Catalytic cracking also produces alkenes.

Decane (C₁₀H₂₂) can undergo cracking to give C₄H₁₀ and two different alkenes.

Complete the equation for this cracking process.

Sulfur dioxide (SO₂) and hydrogen sulfide (H₂S) are both gases.

The two gases react together to form solid sulfur and water.

Complete the chemical equation for the reaction.

State why the sulfur dioxide is reduced in the reaction.

The diagram shows apparatus used to compare the speed at which particles of the two gases diffuse.

cotton wool soaked in pale yellow cotton wool soaked in sulfur dioxide solution solid hydrogen sulfide solution

The two pieces of cotton wool and rubber bungs are put in position at the same time.

A pale yellow solid soon forms.

Explain how the diagram shows that hydrogen sulfide gas diffuses more quickly than sulfur dioxide gas.

Deduce a relationship between the relative formula mass (M_r) of a gas and the speed at which a gas diffuses.

Use the A_r values to help you.

[A_r values: H = 1 S = 32 O = 16]

Sodium hydroxide dissolves in water, forming a strongly alkaline solution.

Ammonia dissolves in water, forming a slightly less alkaline solution.

Identify the ion that makes the sodium hydroxide solution alkaline.

What is a possible pH of ammonia solution?

When ammonia solution reacts with sulfuric acid, a neutralisation reaction occurs and ammonium sulfate forms.

How does the sulfuric acid act in this reaction?

The diagram shows a beaker containing some ammonia solution and a few drops of phenolphthalein indicator.

Dilute sulfuric acid is added to the beaker until it is in excess.

What are the colours of the phenolphthalein indicator before and after adding excess sulfuric acid?

Ammonium sulfate is used by gardeners as a fertiliser because it contains nitrogen.

Explain why the chemical formula of ammonium sulfate is (NH₄)₂SO₄

Refer to the charges on the ions in your answer.

Calculate the relative formula mass of ammonium sulfate, (NH₄)₂SO₄

Calculate the mass, in grams, of nitrogen in 1.0 kg of ammonium sulfate.

A student uses the reaction between zinc and dilute sulfuric acid to prepare some zinc sulfate crystals.

Complete the equation for this reaction by giving the correct state symbols.

State what would be observed during this reaction.

The student adds excess zinc to a beaker of dilute sulfuric acid.

Explain why it is necessary to add excess zinc.

Draw a diagram of the apparatus the student should use to remove the unreacted zinc and collect the zinc sulfate solution.

The student obtains a pure, dry sample of zinc sulfate crystals.

The formula of zinc sulfate crystals is ZnSO₄.7H₂O

Calculate the relative molecular mass (M_r) of zinc sulfate crystals.

The student uses 0.0200 mol of dilute sulfuric acid in her preparation.

Show that the maximum mass of zinc sulfate crystals that the student could obtain is about 6 g.

The student obtains a mass of 4.28 g of zinc sulfate crystals.

Calculate the percentage yield of the zinc sulfate crystals.

Give your answer to three significant figures.

Crude oil is a mixture of hydrocarbons.

Name the process used to separate crude oil into fractions.

Give one use of the kerosene fraction.

One of the hydrocarbons in the refinery gas fraction is an alkane with the structural formula CH₃CH₂CH₂CH₃

Give the name of this alkane.

Calculate the relative molecular mass (M_r) of this alkane.

One of the alkanes in the gasoline fraction has the displayed formula

H H H H H H H

Determine the molecular formula of this alkane.

Give the general formula for the alkanes.

Catalytic cracking is used to convert long‑chain alkanes into shorter‑chain alkanes.

Name the catalyst used in catalytic cracking.

Explain why it is necessary to convert long‑chain alkanes into shorter‑chain alkanes.

Catalytic cracking also produces alkenes.

C₁₁H₂₄ can undergo cracking to give pentane (C₅H₁₂) and two different alkenes.

Complete the equation for this cracking reaction.