Dr. Emanuele Chemistry Tutor - Topic 1 - Principles of Chemistry

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Topic 1: Principles of chemistry

Subtopic 1a: States of matter

1) The element carbon has three common isotopes. These are carbon-12, carbon-13 and carbon-14.

(a) Complete the table to show the number of protons and neutrons in each isotope of carbon. (2)

(b) Explain, in terms of electrons, why the three isotopes have the same chemical properties. (1) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(c) (i) State what is meant by the term relative atomic mass, Ar (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(ii) A sample of carbon contained 98.90% carbon-12 and 1.10% carbon-13. Use this information to calculate the relative atomic mass of carbon in the sample. Give your answer to two decimal places. (3) Relative atomic mass .................................................................................

(Total for Question 1 = 8 marks)

2) Atoms contain three different types of particle. These are electrons, neutrons and protons.

(a) Which one of the three particles has a negative charge? (1)

(b) Which one of the three particles has the smallest mass? (1)

(i) Atoms are neutral because they contain equal numbers of and (1)

(ii) Isotopes are atoms with the same number of but different numbers of in the nucleus. (2)

(d) An atom of magnesium can be represented by the symbol 24 12Mg. Use numbers to complete these statements about this atom.

(i) The atomic number of this atom is . (1)

(ii) The mass number of this atom is . (1)

(iii) The electronic configuration of this atom is . (1)

(Total for Question 2 = 8 marks)

3) This question is about the element beryllium. (a) Use words from the box to complete the sentences about beryllium. Each word may be used once, more than once or not at all. (7)

An atom of beryllium has a central ............................................................ that contains particles called ............................................................ and ............................................................ . Around these particles there are ............................................................ orbiting in ............................................................ . An atom of beryllium has no charge because it contains equal numbers of ............................................................ and ............................................................ . The particles with the lowest mass in an atom of beryllium are called ............................................................ .

(b) Beryllium forms a compound with the formula Be(OH)2

(i) How many different elements are there in Be(OH)2 ? (1) ....................................................................................................................................................................................................................................................................................

(ii) What is the total number of atoms in the formula Be(OH)2 ? (1) ....................................................................................................................................................................................................................................................................................

(Total for Question 6 = 9 marks)

Techniques used in the separation of mixtures include A crystallisation B filtration C fractional distillation D simple distillation For each separation, select the most suitable technique, A, B, C or D, used to obtain the first named substance from the mixture. Each letter may be used once, more than once or not at all.

(a) Pure water from sea water (1) ....................................................................................................................................................................................................................................................................................

(b) Ethanol from a mixture of ethanol and water (1) ....................................................................................................................................................................................................................................................................................

(c) Calcium carbonate from a mixture of calcium carbonate and water (1) ....................................................................................................................................................................................................................................................................................

(d) C uSO4 .5H2 O(s) from CuSO4 (aq) (1) ....................................................................................................................................................................................................................................................................................

(Total for Question 2 = 4 marks)

Subtopic 1b: Elements, compounds and mixtures

A student investigates the pigments found in some vegetables and fruit. She obtains some coloured vegetable and fruit extracts from carrots, tomatoes and sweet potatoes. She places a spot of each extract on chromatography paper, along with spots of the three pigments beta-carotene, chlorophyll and lycopene. Her teacher provides a solvent containing volatile, flammable organic compounds for the experiment. The diagram shows the apparatus at the start of the experiment.

Key to vegetable and fruit extracts and pigments V1 = carrots P1 = beta-carotene V2 = tomatoes P2 = chlorophyll V3 = sweet potatoes P3 = lycopene (a) (i) Explain why it is important for the solvent level to be below the spots. (1) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(ii) State two potential problems that are prevented by fitting the tank with a lid. (2)

1 ................................................................................................................................................................................................................................................................................ ....................................................................................................................................................................................................................................................................................

2 ................................................................................................................................................................................................................................................................................ ....................................................................................................................................................................................................................................................................................

(b) The diagram shows the chromatogram at the end of the experiment.

Key to vegetable and fruit extracts and pigments V1 = carrots P1 = beta-carotene V2 = tomatoes P2 = chlorophyll V3 = sweet potatoes P3 = lycopene Which three of the statements A, B, C, D and E are supported by the chromatogram? Place a cross in three boxes to indicate your choice. (3)

A Chlorophyll is not present in carrots, sweet potatoes or tomatoes.

B Beta-carotene is present in carrots but not present in tomatoes.

C Both beta-carotene and lycopene are present in sweet potatoes.

D Lycopene is present in tomatoes but not present in carrots.

E Both carrots and tomatoes contain a pigment other than beta-carotene, chlorophyll and lycopene.

(c) One of the pigments present in the vegetable extracts is not shown in the chromatogram. It appears as a very faint spot 1.3 cm above the starting line. Calculate its Rf value using the expression Rf = distance travelled by pigment distance travelled by solvent (2)

Rf = .....................................

(d) Suggest a reason why there is a spot on the starting line in the chromatogram for sweet potatoes. (1) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(Total for Question 3 = 9 marks)

A student uses the following method to prepare a sample of hydrated zinc nitrate crystals. step 1 step 2 step 3 put 25cm3 of dilute nitric acid into a beaker add zinc carbonate until it is in excess separate the dilute solution of zinc nitrate from the mixture The student then obtains crystals from the dilute solution of zinc nitrate. (a) Name the piece of apparatus used to measure the nitric acid in step 1. (1) ....................................................................................................................................................................................................................................................................................

(b) How would the student know when she has added an excess of zinc carbonate? (1) .................................................................................................................................................................................................................................................................................... .....................................................................................................................................................................................................................................................................................

(c) Name the separation method used in step 3. (1) ....................................................................................................................................................................................................................................................................................

(d) The student wants to obtain a pure, dry sample of hydrated zinc nitrate crystals from the dilute solution. One method is to leave the solution so that all the water evaporates. Describe another method, involving crystallisation, that the student could use. (4)

(Total for Question 1 = 7 marks)

(a) Substances can be classified as elements, compounds or mixtures. Each of the diagrams below represents either an element, a compound or a mixture. State which one of these is represented by each diagram.

(b) Substances can also be classified as solids, liquids or gases. Each of the diagrams below represents either a solid, a liquid or a gas. State which one of these is represented by each diagram.

Subtopic 1c: Atomic structure

1) The diagram shows the structure of an atom.

(a) Name the central part of an atom. (1) .............................................................................................................................................

(b) Name the positively charged particles in an atom. (1) .............................................................................................................................................

(c) State how the diagram shows that this atom is neutral. (1) ............................................................................................................................................. .............................................................................................................................................

(d) Give the mass number of this atom. (1) .............................................................................................................................................

(e) Give the name of the element containing this atom. Use the Periodic Table to help you. (1) .............................................................................................................................................

(Total for question = 5 marks)

2) Use the Periodic Table to help you answer this question.

(a) (i) Name the element with atomic number 14 (1) .............................................................................................................................................

(ii) Name the element with a relative atomic mass of 11 (1) .............................................................................................................................................

(iii) Name the element in Group 2 and Period 3 (1) .............................................................................................................................................

(b) (i) Determine the number of neutrons in a phosphorus atom with mass number 31 (1) .............................................................................................................................................

(ii) State the electronic configuration of an aluminium atom. (1) .............................................................................................................................................

(iii) State why neon is unreactive. (1) ............................................................................................................................................. .............................................................................................................................................

(Total for question = 6 marks

3) This question is about chemical elements. Use the Periodic Table to help you answer this question. (a) (i) Identify the element with atomic number 5 (1) ............................................................................................................................................. (ii) Give the symbol of a metallic element in Period 3 (1) .............................................................................................................................................

(iii) Identify the element whose atoms contain 14 protons. (1) .............................................................................................................................................

(iv) Identify the element whose atoms have the electronic configuration 2.5 (1) .............................................................................................................................................

(v) Give the name of the compound formed between oxygen and the element with atomic number 13 (1) .............................................................................................................................................

Subtopic 1d: Periodic Table

1) (a) Complete the following sentence. (1) The elements in the Periodic Table are arranged in order of ............................................................................................... .................................................................................................................................................................................................................................................................

(b) Name an element shown in the diagram that is: (2)

(i) a metal .................................................................................................................................................................................................................................

(ii) a halogen ..........................................................................................................................................................................................................................

(c) (i) Name two elements in the diagram that react together to form an ionic compound. (1) ................................................................................................................................... and ....................................................................................................................................

(ii) Draw a dot and cross diagram for the ions in the compound formed in (c)(i).

Show only the outer electrons. Include the charge on each ion. (3)

(d) Chlorine reacts quickly with hot iron to form iron(III) chloride. Bromine reacts less quickly with hot iron to form iron(III) bromide. Suggest how fluorine reacts with hot iron and name the compound formed. (2) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(e) When chlorine gas is bubbled through an aqueous solution of sodium bromide, a displacement reaction takes place. The ionic equation for the reaction is: Cl2 (g) + 2Br− (aq) 2Cl− (aq) + Br2 (aq).

State the colour change that you would observe in the solution during this reaction. (2)

Colour at start ...........................................................................................................................................................................................................................................

Colour at end .............................................................................................................................................................................................................................................

(Total for Question 2 = 11 marks)

2) This question is about bromine and some of its compounds.

(a) Atoms of bromine can be represented as 79Br and 81Br (i) State the number of protons, neutrons and electrons in an atom of 79Br (2) Protons .............................................................................................................................................................................................................................................................

Neutrons .........................................................................................................................................................................................................................................................

Electrons .........................................................................................................................................................................................................................................................

(ii) What name is used for atoms of bromine that have different numbers of neutrons? (1) ....................................................................................................................................................................................................................................................................................

(iii) Why do all atoms of bromine have the same chemical properties? (1) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(iv) The relative atomic mass of bromine is given in the Periodic Table as 80, but a more accurate value is 79.9 Suggest, with a reason, which of the atoms 79Br and 81Br exists in greater numbers in a sample of bromine. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... ..................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(b) Hydrogen bromide (HBr) and sodium bromide (NaBr) are compounds of bromine.

(i) Draw a dot and cross diagram to represent a hydrogen bromide molecule. Show only the outer electrons in each atom. (2) (ii) Explain how the atoms are held together in a hydrogen bromide molecule. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(iii) Explain why sodium bromide has a higher melting point than hydrogen bromide. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(c) A compound has the percentage composition 13.8% sodium, 47.9% bromine and 38.3% oxygen by mass. Calculate its empirical formula. (3)

Empirical formula = ..............................................................

(Total for Question 7 = 16 marks)

Subtopic 1e: Chemical formula equations and calculations

1) Magnesium reacts with dilute hydrochloric acid. The equation for the reaction is Mg(s) + 2HCl(aq) o MgCl2 (aq) + H2 (g)

(a) 0.0960 g of magnesium was added to 25.0 cm3 of 0.400 mol/dm3 hydrochloric acid.

(i) Calculate the amount, in moles, of magnesium used. (2) amount of magnesium = ...................................................... mol (ii) Calculate the amount, in moles, of HCl in the 25.0 cm3 of hydrochloric acid. (2)

amount of HCl = ...................................................... mol

(b) Use your answers from (a) to determine which of the reactants is in excess. Show your reasoning. (2)

The reactant in excess is .................................................................................................................................................................................................................

(Total for Question 4 = 6 marks)

2) (a) Write a chemical equation for the reaction between nitrogen monoxide, NO, and carbon monoxide to form carbon dioxide and nitrogen. (1) .............................................................................................................................................

(Total for question = 1 marks)

3) (a) Iron reacts with chlorine to form iron(III) chloride, FeCl3 (i) Use information from the Periodic Table to calculate the relative formula mass (Mr) of iron(III) chloride. (2)

Mr = ........................................................... (ii)

Complete the chemical equation for the reaction of iron with chlorine. (1)

............................... Fe + ............................... Cl2 → ............................... FeCl3

(Total for question = 3 marks)

4) (i) Complete the chemical equation for the incomplete combustion of octane. (2)

C8H18 + ................................O2 → 5CO + ................................CO2 + ................................H2O

(Total for question = 2 marks)

5) Ocimene is an organic compound that gives some plants their particular smell. The molecular formula of ocimene is C10H16

(a) Calculate the relative formula mass (Mr) of ocimene. (1) Mr = ...........................................................

(b) Using ocimene as an example, explain what is meant by the term empirical formula. (2) ............................................................................................................................................. .............................................................................................................................................

(Total for question = 3 marks)

6) A sample of magnesium contains these percentages of the three isotopes. Mg-24 = 79.00% Mg-25 = 10.00 % Mg-26 = 11.00 % Use this information to show that the relative atomic mass of magnesium is 24.32 (2)

(iv) One mole of magnesium has a mass of 24.32 g. There are 6.022 × 1023 atoms in one mole. Calculate the mass, in grams, of one atom of magnesium. Give your answer to 4 significant figures. (2)

mass = ........................................................... g

Determine the maximum amount, in moles, of magnesium oxide that can be produced from 0.50 mol of magnesium and 0.20 mol of oxygen. (1)

amount = ........................................................... mol (Total for question = 5 marks)

7) This question is about lithium carbonate.

(a) The formula of lithium carbonate is Li2CO3.

Calculate the relative formula mass (Mr ) of lithium carbonate. (1) Mr = ...........................................................

(c) Lithium carbonate decomposes when heated to produce lithium oxide and carbon dioxide. Complete the chemical equation for this reaction. (1) Li2CO3 → ............................................... + ...............................................

(Total for question = 2 marks)

8) (a) Calculate the relative formula mass (Mr) of sodium oxide, Na2O, using information from the Periodic Table. (1)

Mr = ...........................................................

(b) When sodium oxide is heated it reacts to form sodium metal and sodium peroxide, Na2O2 Complete the equation for this reaction. (1)

Na2O →

(Total for question = 2 marks)

9) (a) An organic compound has the percentage composition by mass C = 36.36% H = 6.06% F = 57.58%

(i) Show that the empirical formula of the compound is CH2F (2)

(ii) The relative molecular mass (Mr) of the compound is 66. Determine the molecular formula of the compound. (2)

molecular formula = ...........................................................

(Total for question = 4 marks)

Subtopic 1f: Ionic bonding

1) Hydrogen chloride is formed in the reaction between hydrogen and chlorine. The equation for the reaction is H2 + Cl2 o 2HCl (a) Each molecule in this equation contains the same type of bonding. Name this type of bonding. (1) ....................................................................................................................................................................................................................................................................................

(b) The bonding in a hydrogen molecule is strong. Explain why the boiling point of hydrogen is low. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(c) Explain how the two atoms in a chlorine molecule are held together. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(d) Draw a dot and cross diagram to show the bonding in a hydrogen chloride molecule. Show only the outer electrons in each atom. (2).

(e) Hydrogen chloride gas dissolves in water to form solution A. Hydrogen chloride gas dissolves in methylbenzene to form solution B. A teacher adds a piece of magnesium ribbon to each solution. Explain why she observes effervescence with solution A but not with solution B. (3) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(Total for Question 1 = 10 marks

2) Sodium chloride (NaCl) and silicon dioxide (SiO2 ) both have giant lattice structures. Sodium chloride is an ionic compound. Silicon dioxide is a covalent compound.

(a) (i) Explain why silicon dioxide has a high melting point. (2) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(ii) Suggest why the melting point of silicon dioxide is higher than the melting point of sodium chloride. (1) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(b) State why sodium chloride conducts electricity when molten. (1) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(c) Carbon dioxide is described as a simple molecular substance. State why carbon dioxide (CO2 ) is a gas at room temperature. (1) .................................................................................................................................................................................................................................................................................... ....................................................................................................................................................................................................................................................................................

(Total for Question 2 = 5 marks)

Subtopic 1g: Covalent bonding

1) This question is about nitrogen and some of its compounds. (c) Ammonia is a simple molecule with the formula NH3 (i) Complete the diagram to show the outer shell electrons in ammonia. (2)

(ii) The bonds in ammonia are covalent. Describe the forces of attraction in a covalent bond. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(iii) Explain why ammonia has a low boiling point. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(Total for question = 6 marks

2) The diagram shows the displayed formula of the organic compound methanol, CH3OH (b) The atoms in methanol are held together by covalent bonds. (i) State what is meant by the term covalent bond. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. (ii) Draw a dot-and-cross diagram to show the bonding in a molecule of methanol CH3OH. Show only the outer electrons of each atom. (2)

(Total for question = 4 marks)

3) (iii) Draw a dot-and-cross diagram to represent a molecule of C2H5Cl Show only the outer electrons of each atom. (2) (Total for question = 2 marks)

4) Draw a dot-and-cross diagram to show the bonding in a molecule of ammonia. Show outer electrons only. (2)

(Total for question = 2 marks)

5) Boron and fluorine form a covalent compound that has the molecular formula BF3 Draw a dot-and-cross diagram to show the arrangement of the outer electrons in a molecule of BF3 Use crosses to represent the outer electrons of boron.

Use dots to represent the outer electrons of fluorine. (2)

(Total for question = 2 marks)

6) Nitrogen dioxide and silicon dioxide are compounds containing covalent bonds.

(a) State what is meant by the term covalent bond. (1) ............................................................................................................................................. .............................................................................................................................................

(b) Nitrogen dioxide and silicon dioxide both contain covalent bonds.

Explain why nitrogen dioxide has a much lower melting point than silicon dioxide.

Refer to structure and bonding in your answer. (6) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(Total for question = 7 marks)

Subtopic 1f: Metallic bonding

1) This question is about the metal aluminium.

(a) Aluminium is malleable and conducts electricity.

The diagram shows the arrangement of the ions in aluminium metal.

(i) Explain why aluminium is malleable. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(ii) Explain why aluminium conducts electricity. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(Total for question = 4 marks)

2) (a) Explain why metals conduct electricity but covalent compounds do not conduct electricity. (4)

(b) Hydrogen chloride, HCl, is a covalent substance. When hydrogen chloride is added to water, a solution of dilute hydrochloric acid is formed. This solution does conduct electricity. Name the type of particle in the solution of the dilute hydrochloric acid that allows it to conduct electricity. (1) .............................................................................................................................................

(Total for question = 5 marks)

3) The wire used to connect the power supply to the electrodes is made of copper metal. The diagram shows the arrangement of the ions in a metal.

4) This is a question about metals and their compounds.

(a) State one property of metals. (1) .............................................................................................................................................

(b) Mercury is the only metal that is liquid at room temperature.

(i) Describe the difference in the movement of particles in liquid mercury and in a solid metal. (2) ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(ii) Describe, in terms of electrons, the formation of the ions in magnesium sulfide. Give the charges on the ions. (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(iii) Explain why magnesium sulfide has a very high melting point. (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(Total for question = 9 marks)

5) This question is about copper and its compounds.

(a) Copper is a metal used for electrical wiring. Explain why copper is a good conductor of electricity. (2)

............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(Total for question = 2 marks)

6) Explain, using a labelled diagram, why lead metal is malleable. (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(Total for question = 3 marks)

Subtopic 1i: Electrolysis

1) (a) The teacher then sets up a circuit in a fume cupboard using the pure, dry sample of lead(II) bromide.

(b) Explain why the lamp does not light when the lead(II) bromide is solid. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(c) The teacher heats the lead(II) bromide. When the lead(II) bromide is molten, the lamp lights and bromine forms at the positive electrode.

(i) State what observation would be made at the positive electrode. (1) ............................................................................................................................................. .............................................................................................................................................

(ii) Explain how bromide ions in the molten lead(II) bromide become bromine molecules at the positive electrode. (4) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(d) Write an ionic half-equation for the reaction that occurs at the negative electrode. Include state symbols in your equation. (2)

.............................................................................................................................................

(Total for question = 9 marks)

2) (a) This question is about copper and its compounds. (a) Copper is a metal used for electrical wiring. Explain why copper is a good conductor of electricity. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(b) This apparatus is used to investigate the electrolysis of copper(II) sulfate solution with graphite electrodes.

Copper forms at the negative electrode and oxygen forms at the positive electrode. (i) State what would be observed at each electrode. (2)

negative electrode .............................................................................................................................................

positive electrode .............................................................................................................................................

(ii) The ionic half-equation for the reaction at the negative electrode is Cu2+ + 2e– → Cu State why this is a reduction reaction. (1) ............................................................................................................................................. ............................................................................................................................................. (iii) Explain why the copper(II) sulfate solution becomes paler blue during the electrolysis. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(Total for question = 7 marks)

3) Aluminium is extracted from aluminium oxide (Al2O3) by electrolysis. (ii) Aluminium is produced at the negative electrode.

The ionic half-equation for the reaction is Al3+ + 3e− → Al

State why this is a reduction reaction. (1) ............................................................................................................................................. .............................................................................................................................................

(iii) Complete the ionic half-equation for the reaction at the positive electrode. (2) ...............................

O2− → .............................................................. +............................................................

(Total for question = 3 marks)

4) The diagram shows how hydrogen gas and chlorine gas can be prepared in the laboratory by electrolysis of a concentrated solution of sodium chloride.

(b) The ionic half-equation for the formation of chlorine at the positive electrode is 2Cl− → Cl2 + 2e− (i) State why this reaction is an oxidation reaction. (1)

(ii) Give the ionic half-equation for the formation of hydrogen at the negative electrode. (1) .............................................................................................................................................

(iii) State why it is safer to do this electrolysis in a fume cupboard. (1) ............................................................................................................................................. .............................................................................................................................................

(iv) Suggest why the volume of chlorine collected during this electrolysis is less than the volume of hydrogen collected. (1) ............................................................................................................................................. .............................................................................................................................................

The overall equation for this reaction is 2NaCl(l) → 2Na(l) + Cl2(g) (i)

Explain why sodium chloride needs to be molten rather than solid for electrolysis to occur. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................

(Total for question = 6 marks)

If you need the markscheme, including the examiners' reports for each question, and more exam and teaching materials on this topic, contact me through the contact page

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