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KS3 revision booklet chemistry
Use this booklet to help you revise the chemistry you have studied in Key Stage 3. There are quizzes you can use to test yourself, and diagrams to remind you of key ideas. Why not make a list of questions to test your friends with, or try and make a mind map of some of the key ideas? Remember- a little and often is the best way to revise!
Contents Atoms and elements Atoms and elements quiz Compounds and mixtures Compounds and mixtures quiz Chemical reactions Chemical reactions quiz Rock cycle Rock cycle quiz
Atoms and elements Elements
An element is a simple substance that cannot be split into anything simpler by chemical reactions. Atoms are the smallest particles of an element that can exist. Atoms of one element are all the same, and are different from atoms of all the other elements. There are over 100 different elements. All the elements are shown in the Periodic Table. Each element has a chemical symbol, which is usually one or two letters. A symbol is written with the first letter as a capital, and the second letter is small. carbon
C
oxygen
O
nitrogen
N
hydrogen
H
gold
Au
silver
Ag
copper
Cu
aluminium
Al
Metals and non-metals
The properties of a substance are the words that we use to describe it, or measurements that we can make on it. Metals and non-metals have different properties. Metals
Non-metals
good conductors of heat and electricity
poor conductors of heat and electricity
shiny
dull
solids with a high melting point (except for mercury)
most are solids or gases
found on the left-hand side of the Periodic Table
found on the right-hand side of the Periodic Table
three metals are magnetic
no non-metals are magnetic
metals can burn to form alkaline oxides
non-metals can burn to form acidic oxides
flexible
brittle
Compounds
Elements can join together to make compounds. The name of the compound tells you the elements that are in it. Compounds made from two elements always have a name which ends in ‘-ide’. These elements join together …
… to make these compounds
carbon, oxygen
carbon dioxide
sodium, chlorine
sodium chloride
magnesium, oxygen
magnesium oxide
A chemical formula tells you the name and number of atoms in a compound. The smallest particle of many compounds is called a molecule. Molecules are made up of atoms. Some elements are also made of molecules. For example, a molecule of oxygen contains two oxygen atoms joined together. The formula is O2. Elements
Compounds
Mixtures
atoms of helium (He)
molecules of carbon dioxide (CO2)
a mixture of helium and oxygen
molecules of oxygen (O2)
molecules of water (H2O)
a mixture of carbon dioxide and oxygen
a lump of carbon (C)
a lump of sodium chloride (NaCl)
a lump of bronze (an alloy of copper and tin)
1.
ATOMS AND ELEMENTS QUIZ Which of these things is an element? A salt B water C oxygen D air
2
The number of chemical elements in the world is: A 4. B about 100. C about 1000. D over a million.
3
The element that makes up most of the mass of your body is: A oxygen. B carbon. C calcium. D hydrogen.
4
Chemical elements: A are always solids. B are either solids or liquids. C are always gases. D can be solids, liquids or gases.
5
Which of these metals is not a pure element? A gold B copper C silver D bronze
6
The smallest part of an element is called: A an atom. B a molecule. C a compound. D an ion.
7
An element is something that: A can be split up by a chemical reaction. B cannot be split up by a chemical reaction. C is made up of different kinds of atom. D is a mixture of atoms and molecules.
8
The correct way to write the chemical symbol for calcium is A CA B Ca C ca D Ca
Compounds and mixtures Elements are simple substances which cannot be split up in chemical reactions. Atoms are the smallest particles of an element that can exist. Atoms of an element are all the same. Each element has its own chemical symbol. For example, the chemical symbol for oxygen is O. Some elements have their atoms joined to each other in small groups called molecules. Oxygen is an example.
A molecule of oxygen consists of two oxygen atoms joined together.
Compounds
Elements can join together to make compounds. A compound contains two or more elements joined together. The name of the compound tells you the elements that are in it. Compounds made from two elements always have a name which ends in ‘-ide’. Many compounds exist as atoms attached to each other in small groups – molecules.
A molecule of water.
The chemical formula tells you the numbers of atoms of each element in a compound. Each element in the chemical formula is shown by its chemical symbol. For example:
A compound always contains the same elements in the same ratio. The properties of a compound are different from the elements that make it up. For example, hydrogen is an explosive gas and oxygen will relight a glowing splint but water is a liquid which will put fires out.
Chemical reactions
Compounds can react chemically by mixing them with other chemicals, or by using heat or electricity. You can tell that a chemical reaction has occurred if there is a colour change or when a gas is given off. Most chemical reactions also involve an energy change. This is usually in the form of heat, but can also involve light being given off, for example, in burning (combustion). In a chemical reaction a new substance is always formed. Most chemical reactions are not easily reversed (they are irreversible). Some chemical reactions take place just by mixing. When you make a solid by mixing two liquids, the solid is called a precipitate. Other chemical reactions need energy to start them off. This energy can be in the form of heat, light or electricity. When you use energy to split up compounds they are decomposed. We can write word equations to show a chemical reaction. The chemicals that you start with are called the reactants. The chemicals at the end are called the products. For example: magnesium + oxygen reactants
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magnesium oxide product
Physical changes
In a physical change no new substance is formed. Melting, evaporating, condensing and freezing are all examples of physical changes. For example:
Mixtures
Elements and compounds can also be mixed together. A mixture is easier to separate than the elements in a compound. Soil, river water and sea water are examples of mixtures that occur naturally. Elements and compounds melt and boil at a fixed temperature. Mixtures do not have definite melting points and boiling points. Air is a mixture of gases – most of the air is nitrogen and oxygen. The gases in the air can be separated by fractional distillation.
Compounds and mixtures quiz
1
An atom is: A the smallest particle that can exist. B a group of particles that are all the same. C the smallest particle of a compound that exists under normal conditions. D the smallest particle of an element that exists under normal conditions.
2
A molecule is: A the smallest particle that can exist. B the smallest particle of an element that can exist. C two or more atoms chemically joined together. D the same as an atom.
3
The number of types of atom in a compound is: A only one. B one or two. C two or more. D three or more.
4
How many different elements are there in the compound with the formula NH3? A one B two C three D four
5
Which of these things does not show that a reaction has occurred? A The mixture gets hotter. B The substance changes from a liquid to a solid. C The mixture changes colour. D Bubbles of gas form in the mixture.
6
The substances that you get at the end of a chemical reaction are called: A reactants. B chemicals. C products. D gases.
7
Which of these changes is a chemical reaction? A Melting some margarine in a pan. B Boiling a kettle of water. C Frying an egg. D Cooling a drink by putting an ice cube in it.
8
Complete this word equation: sodium carbonate + copper sulphate ® sodium sulphate + ____________ A copper sulphate B copper oxide C sodium carbonate D copper carbonate
Reactions of metals and metal compounds
The properties of a substance are the words that we use to describe it, or measurements that we can make on it. Metals and non-metals have different properties. Metals …
Non-metals …
are good conductors of heat and electricity
are poor conductors of heat and electricity (except for carbon in the form of graphite which conducts electricity)
are shiny
are dull
are solids, often with high melting points (except for mercury)
are mostly solids or gases
are found on the left-hand side of the Periodic Table
are found on the right-hand side of the Periodic Table
are sometimes magnetic – three metals are magnetic (iron, cobalt and nickel)
are never magnetic
form basic oxides
form acidic oxides
are rigid when thick and bendy when thin
are brittle
can be hammered into shape
cannot be hammered into shape – the solid ones break
Using metals
Metals and non-metals have different uses because of their different properties.
Aluminium is used for power lines because it is light and it is a good conductor of electricity.
Iron and steel are used for bridges because they are strong and cheap.
Gold is used for jewellery because it does not corrode and looks nice.
Metals and acids
Many metals react with acids. Some unreactive metals will only react very slowly with strong acids, some will not react at all. Some metals are more reactive and explode when added to acid. When a metal reacts with an acid, hydrogen gas is given off. The reaction also produces a compound called a salt. There are three main types of salt: Chlorides are made when hydrochloric acid is used. Sulphates are made when sulphuric acid is used. Nitrates are made when nitric acid is used.
The general equation is: acid + metal
salt + hydrogen
For example: hydrochloric acid + zinc
zinc chloride + hydrogen
We can test for hydrogen by putting a burning splint into a test tube of gas. If hydrogen is present, it will explode with a squeaky ‘pop’.
Bases
Bases are compounds which react with acids. All metal oxides, metal hydroxides and metal carbonates are bases. Bases which dissolve in water are called alkalis (e.g. sodium hydroxide).
Metal oxides and hydroxides and acids
A metal oxide or a metal hydroxide reacts with an acid to form water and a salt. This reaction is called neutralisation. The general equation is: acid + metal oxide (or hydroxide)
salt + water
For example: hydrochloric acid + potassium hydroxide sulphuric acid + copper oxide
potassium chloride + water
copper sulphate + water
We can check to see if neutralisation has occurred using universal indicator. The pH of the solution gets closer to neutral (pH7).
Patterns of reactivity Metals may react with substances around them in the environment such as air, water and acids. Some metals react very easily or quickly, such as Potassium or Sodium. They are reactive. Other metals do not react very easily and are described as unreactive. The most reactive metals are found on the left-hand side of the Periodic Table. Less reactive metals are found in the centre of the Periodic Table. Some gases are more reactive than others. In the air, oxygen is the most reactive gas. Nitrogen is not very reactive. When metals react with the oxygen in the air they form oxides. metal + oxygen
metal oxide
The metals that react quickly with air also tend to react with water. When metals react with water they form hydrogen gas and a metal hydroxide. metal + water
metal hydroxide + hydrogen
The metals that react with water also react very quickly with acids. Some metals that don’t react with water do react with acids. When metals react with acids, they produce hydrogen and a salt. metal + acid
salt + hydrogen
The name of the salt formed depends on the name of the acid: • • •
sulphuric acid makes sulphates nitric acid makes nitrates hydrochloric acid makes chlorides.
Reactivity Series
Metals can be arranged in a Reactivity Series. The most reactive metals are placed at the top of the table. More reactive metals can displace less reactive metals from their compounds. In a displacement reaction, the more reactive metal will form a compound, and the less reactive metal is left on its own as the pure element. For example, iron is more reactive than copper, so it will displace copper from a compound. iron + copper chloride
iron chloride + copper
Zinc is more reactive than iron, so iron will not displace zinc from a compound. iron + zinc chloride
no reaction
You can use displacement reactions to work out the position of a metal in the Reactivity Series. For instance, zinc will displace lead from a compound, so we know that zinc is more reactive than lead. The Reactivity Series can also be used to predict whether reactions will occur. The reactivity of metals can be linked to their uses. Metals used for construction need to have a low reactivity, otherwise they will corrode away. Some metals, such as aluminium, have a natural protective oxide layer. Others, such as iron, have to be protected from corrosion, e.g. by painting. Many low reactivity metals have been known for hundreds or thousands of years. They can be extracted by heating their compounds in a fire. More reactive metals are extracted by electrolysis. This means that they have only been discovered in the last two hundred years, since the invention of the electric battery.
1
CHEMICAL REACTIONS QUIZ When some acid is put onto a piece of metal: A there is always a reaction which burns a hole in the metal. B there is never a reaction. C some metals will react with the acid and produce bubbles of gas. D there is always a reaction, which produces a powder.
2
Which of the following is the correct way to test for hydrogen gas? A Bubble the gas through limewater. B Bubble the gas through universal indicator solution. C Put a glowing splint into a tube of the gas (the splint will burn brightly). D Put a burning splint into a tube of the gas (the gas will explode with a squeaky pop).
3
If an acid reacts with a metal, the products are: A a salt and water. B a salt and hydrogen gas. C only hydrogen gas. D a salt, water and carbon dioxide.
4
Which of the following is not needed to make a prediction about the products of a reaction between a metal and an acid? A general information about the reactions between metals and acids B information about the properties of the metal C the name of the metal used D the name of the acid used When some acid is put onto a piece of rock: A it always reacts and gives off a gas. B it reacts if the rock contains a carbonate. C it always reacts explosively and shatters the rock. D it won’t react. The best test for carbon dioxide uses: A universal indicator solution. B a burning splint. C litmus paper. D limewater.
5
6
7
When an acid reacts with a metal carbonate, the products are: A the metal and carbon dioxide. B a salt and water. C carbon dioxide, water and a salt. D the metal, a salt and water.
8
Which of these is not a sign that a reaction has taken place? A The substance catches fire. B The substance has changed from a solid to a liquid. C A gas is given off. D There is an explosion.
The rock cycle
The Earth is continually changing. Rocks are weathered and eroded and new rocks are being formed. The processes which make rocks, weather them and change them are linked together in the rock cycle.
Sedimentary rocks
Rock fragments, formed as a result of weathering and erosion, are transported by rivers, and the fragments get worn down. Small rock fragments are called grains. When the water slows down, some of the grains are deposited at the bottom of rivers, lakes or seas, and form sediment. Layers of sediment collect on the sea bed, and the bottom layers get squashed. The grains of sediment are forced closer together (compacted) and the water is squeezed out from between the grains. Minerals in the sediment ‘glue’ the grains of rock together (cementation). Eventually, sedimentary rock is formed. The composition of sedimentary rocks varies and depends on the way they were formed. For example, there are different types of limestone – chalk is formed from the shells of microscopic animals, coquina is formed from larger shell fragments and oolite is formed from sediments deposited when sea water evaporated.
If any animals or plants get trapped in the sediment, they may form fossils.
Igneous rocks
Molten rock is called magma. If the molten rock flows out of volcanoes it is called lava. Igneous rocks are formed when magma cools down. Lava cools down quite quickly, and forms igneous rocks with small crystals (like basalt). Magma underground cools down much more slowly and forms rocks, like granite, with bigger crystals.
Metamorphic rocks
Sedimentary or igneous rocks can be changed by heat or pressure into new kinds of rock, called metamorphic rocks. Metamorphic rocks have different properties from the sedimentary or igneous rocks they were made from.
1. The word metamorphic means: A deposited. B crushed. C changed. D sedimentary.
ROCK CYCLE QUIZ
2
Which of the following statements is true? A Marble is formed from limestone. B Marble is not a metamorphic rock. C Slate is formed from granite. D Gneiss is formed from marble.
3
Which statement describes some of the ways in which metamorphic rocks are different from sedimentary rocks? A Metamorphic rocks do not contain crystals and are very porous. B Metamorphic rocks are softer, more porous and have large grains. C Metamorphic rocks may be harder, less porous and have crystals which may be lined up. D Metamorphic rocks are softer, less porous and may contain clear fossils.
4
Metamorphic rocks are formed by the effects of: A the high pressure and low temperature inside the Earth. B the high pressure and high temperature inside the Earth. C the low pressure and high temperature inside the Earth. D the low pressure and low temperature inside the Earth.
