AQA GCSE (9–1) Chemistry topics for Combined Science Foundation Support Workbook
Sunetra Berry
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Introduction This workbook will help you build your confidence in answering Chemistry questions for GCSE Combined Science, Foundation tier. It gives you practice in using key scientific words, writing longer answers and applying maths and practical skills.
The opening summary shows what definitions you need to learn.
Learn how to answer test questions by seeing part of the answer filled in. This will help you develop the skills you need to write longer answers, or to use maths in science.
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There are lots of Support notes to help you out. Look out for tips on how to identify key words in the question, how to give a good answer or how to do a calculation.
The amount of support gradually decreases throughout the workbook. As you build your skills you should be able to complete more of the questions yourself.
There are answers to all the questions at the back of the book. You can check your answers yourself or your teacher might tear them out and give them to you later to mark your work.
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Contents Section 1 ● Atomic structure and the periodic table Atoms, elements and compounds Mixtures Compounds, formulae and equations Scientific models of the atom Sizes of atoms Relative masses and charges of subatomic particles Isotopes Electronic structure Development of the periodic table Metals and non-metals Elements in Group 0 Elements in Group 1 Elements in Group 7
Using electrolysis to extract metals Electrolysis of a solution 4 5 6 8 9 10 12 12 13 14 15 17 18
57 58
Section 5 ● Energy changes in reactions Exothermic and endothermic reactions Reaction profiles
60 62
Section 6 ● Rates of reactions Measuring rates of reaction Collisions and reactions Effect of concentration and pressure Effect of surface area Effect of temperature Effect of a catalyst Reversible reactions Reversible reactions and equilibrium
64 65 66 67 68 69 71 72
Section 2 ● The three states of matter The three states of matter Ionic bonding Dot and cross diagrams for ionic compounds Properties of ionic compounds Covalent bonding in small molecules Dot and cross diagrams for covalent compounds Properties of small molecules Polymers Giant covalent structures Properties of giant covalent structures Graphene and fullerenes Metallic bonding Properties of metals and alloys
20 21 22 23 24 25 26 27 28 30 31 32 33
Section 3 ● Quantitative chemistry Writing formulae Balanced equations Chemical measurements Mass changes when a reactant or product is a gas Relative formula mass Concentration of solutions
Crude oil Alkanes Fractional distillation and petrochemicals Properties of hydrocarbons Combustion of fuels Cracking and alkenes
73 74 75 76 77 78
Section 8 ● Chemical analysis Pure substances, mixtures and formulations Chromatography Chromatography and Rf values Tests for common gases
79 80 80 81
Section 9 ● Chemistry of the atmosphere 34 35 36 39 40 42
Earth’s atmosphere – now and in the past Changes in oxygen and carbon dioxide Greenhouse gases Global climate change Carbon footprint Atmospheric pollutants
83 84 85 86 88 89
Section 10 ● Using resources
Section 4 ● Chemical changes Metal oxides Reactivity series Reactivity series – displacement Extraction of metals Reactions of acids and metals Neutralisation of acids and making salts Acids, metal carbonates and making salts Making soluble salts pH scale and neutralisation The process of electrolysis Electrolysis of molten ionic compounds
Section 7 ● Organic chemistry
44 44 46 47 48 49 51 52 53 54 56
What does the Earth provide for us? Safe drinking water Desalination Waste water treatment Life cycle assessment (LCA) Ways of reducing the use of resources
90 91 92 93 94 96
Periodic Table
98
Answers
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Section 1: Atomic structure and the periodic table
Atoms, elements and compounds • • • •
All substances are made of atoms; the atom is the smallest part of an element that can exist. Atoms of each element are represented by a chemical symbol. All the known elements are found on the periodic table. Compounds contain two or more elements chemically combined.
1.
Which two elements are correctly matched to their symbols? Support
Tick two boxes. copper, Cu sodium, Cl chlorine, Ch carbon, C. 2.
[2 marks]
You will be given a copy of the periodic table in the exam (see page 98). You can look up the symbols of the elements on the periodic table. You will only be asked to do this for the first 20 elements.
Look at the diagrams.
A a
B
C
D
Which diagram shows a molecule of an element? Tick one box. A
b
B
✓ C
D
[1 mark]
D
[2 marks]
D
[2 marks]
Which two diagrams show elements? Tick two boxes box. A
c
B
C
Which two diagrams show compounds? Tick two boxes box. A
B
C
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1 3.
Which one of the following statements is false? Tick one box. CO2 is a compound made of one carbon atom and two oxygen atoms. MgCl2 is made from the elements magnesium and chlorine. O2 is a compound made from two O atoms. Fe is an element.
4.
[1 mark]
Look at the following models:
A a
B
C
Which represents the element oxygen? Tick one box. A
b
B
C
[1 mark]
Which represents the compound carbon dioxide? Tick one box. A
c
B
C
[1 mark]
C
[1 mark]
Which represents gases in air? Tick one box. A
B
Mixtures filtration
crystallisation
distillation
chromatography
crystallising dish
crystals
• A mixture consists of two or more elements or compounds not chemically combined together. • Mixtures can be separated by physical processes such as filtration, crystallisation, simple distillation and chromatography. No chemical reactions are involved. • Compounds can only be separated into elements by chemical reactions.
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1.
Which of the following substances are elements, compounds or mixtures? iron oxide
magnesium
oil and water
sodium chloride
salt solution
sodium
Elements: magnesium and
[2 marks]
Compounds:
and
Mixtures: 2.
[2 marks]
and
[2 marks]
Daw a line from each mixture to the method used to separate that mixture. You need to draw four lines. Mixture
Method of separation
sand and water
chromatography
dyes
distillation
lavender oil and water
crystallisation
salt and water
filtration
[4 marks]
Compounds, formulae and equations • Compounds contain two or more elements chemically combined in fixed proportions. • The formula of a compound shows how many of each type of atom are present, using element symbols and subscripts (small numbers). • Symbol equations for chemical reactions are balanced in terms of the numbers of atoms of each element involved on both sides of the equation. • A number is added in front of a formula in an equation to balance the equation. • When a chemical reaction occurs, one or more new substances are made. Chemical reactions can be represented by word equations or equations using formulae.
1.
Write a word equation for the following reactions. a
When iron burns in air, it reacts with oxygen to make iron oxide.
iron + oxygen → iron oxide b
When magnesium burns in air, it reacts with oxygen to make magnesium oxide. +
c
[1 mark]
→
[1 mark]
When sodium is placed in a jar of chlorine, sodium chloride is made. +
→
[1 mark]
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1 2.
Give the names of the elements and the numbers of atoms of each element in the following compounds. a
MgSO4 Elements: magnesium, sulfur and oxygen
[1 mark]
Number of each element:
Mg atoms 1 ; S atoms b
; O atoms 4
[1 mark]
CaCO3 Elements:
[1 mark]
Number of each element: Ca atoms c
; C atoms
; O atoms
[1 mark]
Mg(OH)2 Elements:
[1 mark]
Support
[1 mark]
When there are brackets, everything in the brackets is multiplied by the number outside the brackets.
Number of each element: Mg atoms d
; O atoms
; H atoms
Ca(NO3)2 Elements:
[1 mark]
Number of each element: Ca atoms 3.
; N atoms
; O atoms
[1 mark]
The table shows which groups certain elements belong to. Group 1
Group 2
Group 6
Group 7
Na
Mg
O
Cl
K
Ca
S
Br
Elements from Group 1 and elements from Group 7 combine to make compounds in a fixed ratio of 1 : 1. Write the formula of the following compounds: a
sodium chloride, NaCl
[1 mark]
b
potassium chloride,
[1 mark]
c
potassium bromide,
[1 mark]
Elements from Group 2 and Group 6 combine to make compounds in a fixed ratio of 1 : 1. Write the formula of the following compounds: d
magnesium oxide,
[1 mark]
e
calcium sulfide,
[1 mark]
f
calcium oxide,
[1 mark]
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Elements from Group 2 and elements from Group 7 combine to make compounds in a fixed ratio of 1 : 2. Write the formula of the following compounds: g
magnesium chloride, MgCl 2
[1 mark]
h
calcium iodide,
[1 mark]
i
magnesium bromide,
[1 mark]
Support A ratio of 1 : 2 means there are twice as many of the Group 7 atoms as there are of the Group 2 atoms.
Elements from Group 1 and Group 6 combine to make compounds in a fixed ratio of 1:2. Write the formula of the following compounds:
4.
j
sodium sulfide, Na 2S
[1 mark]
k
potassium sulfide,
[1 mark]
l
sodium oxide,
[1 mark]
Which one of the following reactions is not balanced? Support
Tick one box. 2Mg + O2 → 2MgO
C + O2 → CO2
To make sure the equation balances, check you have the same numbers of atoms of each element on each side of the equation.
Na + Cl2 → NaCl [1 mark]
5.
Balance the following equations: a
2
Fe +
b
K+
c
Cu +
O2 → Cl2 → O2 →
2 FeO
[2 marks]
KCl
[2 marks]
Cu2O
[2 marks]
Scientific models of the atom • Before the discovery of the electron, people thought atoms could not be divided up into smaller particles. • The discovery of the electron led to the ‘plum pudding’ model of the atom. • Alpha particle scattering experiments led to the idea that the mass of an atom was concentrated at the centre (the nucleus) and that the nucleus was charged. • Work by Bohr and Chadwick led to the idea of protons and neutrons inside the nucleus and electrons orbiting the nucleus at specific distances.
+
–
–
–
+ –
+
+ – –
+
+ –
–
+ +
–
–
+
+
–
+ –
electron
Plum pudding model electron
neutron
proton
Bohr model
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1 1.
Complete the sentences to compare the plum pudding and nuclear models of the atom. Use words from the box. electrons
negative
nucleus
positive
protons
In the plum pudding model the atom is a ball of
charge. There are particles called
spread out randomly. In the nuclear model, each atom has a
in the centre. This central area has a
charge. 2.
[4 marks]
Which one of the following statements is false? Tick one box. Niels Bohr adapted the nuclear model of the atom. James Chadwick discovered protons. Electrons were discovered before the nucleus.
3.
[1 mark]
In the alpha particle scattering experiment, alpha particles were fired at thin metal foil. Alpha particles are positively charged. How did the results of the alpha particle scattering experiment show that the plum pudding model could not be correct? Tick one box. The alpha particles were not affected so there could not be any positive charge inside the atom. Some of the alpha particles changed direction so the centre of the atom must be positively charged. The alpha particles were attracted to the metal so there could not be any positive charge inside the atom. [1 mark]
4.
Compare the position of the electrons in the plum pudding model with the Bohr model.
[1 mark]
Support A compare question means give similarities or differences. You will need to mention both parts in the comparison. Good words to use in a compare answer are ‘both’, ‘however’ and ‘but’.
Sizes of atoms • Atoms are very small, having a radius of about 0.1 nm (1 × 10–10 m). • The radius of a nucleus is less than 1/10 000 of that of the atom (1 × 10–14 m).
1.
How many nanometres are there in 1 m? Tick one box. 90
9000
1 000 000
1 000 000 000
[1 mark]
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2.
Which of the measurements below is another way of writing 1 nanometre (nm)? Tick one box. 1 × 10–9 m
3.
1 × 109 m
[1 mark]
Which of the measurements below is another way of writing 1 × 10–10 m? Tick one box. 10 × 10–9 m
4.
0.1 × 10–9 m
[1 mark]
An atom has a diameter of about 2 × 10–10 m
Support A negative power of ten means a number less than 1. The more negative the power of 10, the smaller the number. 10–10 m is 10 times smaller than 10–9 m.
How many nanometres is this? Tick one box. 0.2 nm 5.
2 nm
20 nm
[1 mark]
The radius of the nucleus is about one ten-thousandth (1/10 000) of the radius of an atom. The radius of an atom is 0.1 nm. What is the approximate radius of the nucleus? Tick one box. 10–4 nm
10–5 nm
10–6 nm
[1 mark]
Relative masses and charges of subatomic particles Name of particle
Relative charge
Relative mass
Proton
+1
1
Neutron
0
1
Electron
–1
very small
• Protons and electrons have equal but opposite charges. Neutrons are neutral. • Atoms have no overall charge – the number of electrons equals the number of protons. • All atoms of the same element have the same number of protons; atoms of different elements have different numbers of protons. • The number of protons is called the atomic number. • The sum of the protons and neutrons in an atom is its mass number. • Atoms can be represented as: (Mass number) (Atomic number)
23 11
Na
• An atom can gain or lose electrons to form an ion. • Almost all the mass of the atom is in the nucleus.
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1 1.
The diagram shows the structure of an atom. C
2.
a
How many protons are there in this atom? 6
[1 mark]
b
How many electrons are there?
[1 mark]
c
How many neutrons are there?
[1 mark]
An atom of oxygen has a mass number of 16. The atomic number of oxygen is 8.
3.
a
How many neutrons are there in the nucleus of this atom?
[1 mark]
b
How many electrons are there in one atom of oxygen?
[1 mark]
Which one of the following statements is true? Tick one box. All atoms have the same numbers of protons, neutrons and electrons. All atoms have the same numbers of protons and electrons. All atoms have the same numbers of protons and neutrons.
4.
5.
[1 mark]
State one similarity and one difference between the lithium atom and the lithium ion. Similarity:
[1 mark]
Difference:
[1 mark]
Complete the table to show the number of protons, neutrons and electrons in each atom or ion. Atom or ion 14 7
N
Number of protons
Number of neutrons
Number of electrons
7
7
7
56 26
Fe
27 13
Al
13
Al3+
10
27 13
23 11
Na+
16 8
6.
O2–
[6 marks]
Complete the sentences. Use words from the box. electrons
neutrons
mass number
The nucleus of an atom contains protons and called the
atomic number . The sum of mass of these particles is
. The number of protons is called the
neutral, so the number of protons equals the number of
. The atom is .
[4 marks]
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Isotopes • Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element. • The relative atomic mass of an element is an average value that takes into account how abundant the isotopes of the element are.
1.
2.
35 17
CI
37 17
CI
two isotopes of chlorine
Give the numbers of protons and neutrons in the isotopes of carbon: a
In 136C there are 6 protons and 7 neutrons.
[2 marks]
b
In 146C there are
protons and
neutrons.
[2 marks]
c
In 126C there are
protons and
neutrons.
[2 marks]
Which two of the following statements give the correct description of isotopes? Tick two boxes. Isotopes of the same element contain the same number of protons. Isotopes of the same element contain the same number of neutrons. Isotopes of the same element have the same physical properties. Isotopes of the same element have the same chemical properties.
[2 marks]
Electronic structure • • • •
The electrons in an atom occupy the lowest available energy levels (innermost shells). The first shell (nearest the nucleus) takes two electrons. The second and third shells each take up to eight electrons. We can show the electronic structure of an atom on a diagram or with numbers – for this diagram the electronic structure is 2,8,1. • Elements in the same column of the periodic table have the same number of electrons in the outer shell. This is what gives them similar chemical properties.
1.
Each magnesium atom has 12 electrons. Complete the electronic structure of magnesium in the diagram.
[2 marks]
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1 2.
Complete the table. Support Element
Number of electrons
Electronic structure
Lithium
3
2,1
Boron Fluorine
You will be given a copy of the periodic table in the exam (see page 98). You can look up the atomic number of the elements on the periodic table.
Phosphorus 3.
[8 marks]
Draw one line to match each atom to its electronic structure. You need to draw four lines. Atom
4.
Electronic structure
C
2
Ar
2,4
He
2,8,8
O
2,6
[4 marks]
Complete the sentences about the periodic table. Elements are placed in columns called
.
Elements with the same number of electrons in the outer shell are
.
[2 marks]
Development of the periodic table • Early periodic tables: – put elements in vertical groups – arranged the elements in order of atomic weight – element in the columns did not always have similar chemical properties. • Mendeleev’s periodic table: – put elements with similar properties in the same vertical group – left gaps for elements he thought had not yet been discovered – arranged the elements in order of atomic weight but swapped some elements around so that the patterns of chemical properties fitted better. • Elements in the modern periodic table are arranged in order of atomic number. • The existence of isotopes explains why the order based on atomic weights doesn’t always work.
1.
How is the modern periodic table arranged? Tick one box. in order of atomic number
in order of atomic weight
in order of mass number
in order of neutron number
[1 mark]
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2.
Which statement for elements in the same column is true? Tick one box. They have similar chemical properties. They have similar melting points. They have the same atomic weight.
3.
a
[1 mark]
Which two of the following substances have the same chemical properties? Tick two boxes. sodium
b
chlorine
hydrogen
potassium
iron
[2 marks]
Give a reason for your answer. [1 mark]
4.
Mendeleev put 60 known elements into a table. He put elements with similar chemical properties in columns, known as groups. Some groups in this table had gaps. a
What were the gaps for? [1 mark]
b
Which statement explains why Mendeleev left gaps? Tick one box. To keep elements with similar atomic weights together. To keep elements with similar chemical properties together. To keep elements with similar physical properties together.
[1 mark]
Metals and non-metals • Metals are found to the left and bottom of the periodic table. • Non-metals are found to the top and the right of the periodic table. • Metals react to form positive ions, and non-metals react to form negative ions.
1.
State whether the following elements are metals or non-metals. Use the periodic table on page 98. a
Scandium is a
.
[1 mark]
b
Polonium is a
.
[1 mark]
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1 2.
Suggest two differences in the physical properties of scandium and polonium. Give a reason for each difference. a
Scandium will have a
melting
point and boiling point than polonium because . b
Scandium will have a
[2 marks] density than polonium
Support This question asks you to make suggestions. Your answer should link what you already know and the information you have worked out from the question.
because 3.
4.
.
[2 marks]
a
Are the elements in Groups 1 and 2 metals or non-metals?
[1 mark]
b
Are the elements in Groups 6 and 7 metals or non-metals?
[1 mark]
The atomic structure of metals and non-metals is related to their position in the periodic table. Complete the sentences. a
Group 1 elements all have They lose electrons to form
b
Group 2 elements all have They lose electrons to form
electron(s) in their outer shell. ions.
[2 marks]
electron(s) in their outer shell. ions. electrons to make positive ions.
[2 marks]
c
All metals
d
Group 6 elements all have
electron(s) in their outer shell.
[1 mark]
e
Group 7 elements all have
electron(s) in their outer shell.
[1 mark]
f
All non-metals
electrons to make negative ions.
[1 mark]
[1 mark]
Elements in Group 0 • The elements in Group 0 are called the noble gases. • They are unreactive and do not easily form molecules, as they have a stable arrangement of electrons with a full outer shell. • The boiling points of noble gases increase with increasing relative atomic mass.
1.
Complete the sentence. Elements in Group 0 are called the
.
[1 mark]
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2.
Which sentences about the elements in Group 0 are correct? Tick two boxes. They are unreactive. They form compounds with metal elements. They have no electrons in their outer shell. They are all non-metals.
3.
[2 marks]
Which of these gases are noble gases? Tick two boxes. carbon dioxide helium neon nitrogen oxygen.
4.
[2 marks]
Complete the sentences to explain why noble gases don’t form molecules. electrons in their outer shell, except for
Atoms of noble gases have helium, which has only
electrons.
This arrangement of electrons means that atoms of noble gases do not easily form 5.
with other atoms.
[3 marks]
Going down the group, how does the boiling point of the noble gases change? Tick one box. decrease
increase
stay the same
[1 mark]
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1 Elements in Group 1 • • • • • • •
The elements in Group 1 are known as the alkali metals. They are very reactive. They have similar reactions because they all have one electron in the outer shell. Alkali metals react with oxygen to make oxides. Alkali metals react with chlorine to make chlorides. Alkali metals react with water to make hydroxides – hydrogen is given off. The reactivity of the alkali metals increases as you go down the group (the reactions get more violent).
1.
Which of these metals are alkali metals? Tick two boxes. calcium iron lithium magnesium potassium.
2.
[2 marks]
Which sentence about the alkali metals is not correct? Tick one box. They have one electron in their outer shell. They are unreactive metals. The reactivity of alkali metals increases as you go down the group. They have similar chemical properties.
3.
4.
[1 mark]
Complete the following word equations for the reactions of the alkali metals. a
lithium + oxygen →
b
sodium + water →
c
potassium + chlorine →
[1 mark] +
[2 marks] [1 mark]
Use the correct state symbols from the box to complete the following chemical equation. aq
s
I
g
potassium
+
water
→
2K(s)
+
2H2O(l)
→
potassium hydroxide 2KOH(
)
+
hydrogen
+
H2(
)
[2 marks]
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5.
Which of the following alkali metals has the most vigorous reaction with water? Tick one box. lithium
6.
potassium
sodium
[1 mark]
Describe the trend in reactivity as you go down Group 1.
[1 mark] Support [1 mark]
7.
8.
Balance the following equations for the reactions of the alkali metals with water. a
Na +
b
K+
H2O → H2O →
NaOH + KOH +
H2 H2
[1 mark] [1 mark]
Potassium is an element in Group 1.
A trend in the results means they have a pattern.
Support To make sure the equation balances, check you have the same numbers of atoms of each element on each side of the equation. If only one atom or molecule is needed there is no need to place ‘1’ before it.
Describe the reaction of potassium with water. Include what you would observe.
I would observe bubbles
Support
and
are produced.
The reaction is very
.
[3 marks]
To describe a reaction you need to include the names of the products. Observe means you need to say what you would see happening.
Elements in Group 7 • • • • • •
The Group 7 elements are known as the halogens. These elements are molecules made of pairs of atoms. They have similar reactions because they all have seven electrons in the outer shell. The reactivity of elements in Group 7 decreases going down the group. A more reactive halogen displaces (takes the place of ) a less reactive halogen from a solution of its salt. The further down the group an element is, the higher its relative molecular mass, melting point and boiling point.
1.
Name two halogens. [2 marks]
2.
Bromine has the chemical symbol Br. What is the formula for a molecule of bromine? Tick one box. B
Br
B2
Br2
[1 mark]
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