KS3 Science

Chemistry

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Science KS3 225 questions

KS3 Science › Chemistry

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The particulate nature of matter

1.

What is the particle model of matter?

Matter is made of tiny particles that are always moving.
2.

How are particles arranged in a solid?

Particles are packed closely together in a fixed, regular arrangement.
3.

How do particles move in a solid?

They vibrate around fixed positions.
4.

How are particles arranged in a liquid?

Particles are close together but arranged irregularly.
5.

How do particles move in a liquid?

They move around and slide past each other.
6.

How are particles arranged in a gas?

Particles are far apart and spread out randomly.
7.

How do particles move in a gas?

They move quickly in all directions.
8.

Why does a solid keep a fixed shape?

The particles are held closely together and can only vibrate around fixed positions.
9.

Why can a liquid flow and take the shape of its container?

The particles can move and slide past each other.
10.

Why can a gas spread out to fill its container?

The particles are far apart and move freely in all directions.
11.

How does the distance between particles differ in solids, liquids and gases?

Particles are closest together in solids, further apart in liquids and much further apart in gases.
12.

How does the movement of particles differ in solids, liquids and gases?

Solid particles vibrate, liquid particles move around each other, and gas particles move rapidly in all directions.
13.

What happens to particles when a substance is heated?

They gain energy and move faster.
14.

What happens to particles when a substance is cooled?

They lose energy and move more slowly.
15.

What happens to the spacing between particles when a substance is heated?

The particles usually move further apart.
16.

What is gas pressure?

Gas pressure is the force caused by gas particles colliding with the walls of a container.
17.

What causes gas pressure?

Moving gas particles colliding with the walls of their container.
18.

How does increasing the temperature of a gas affect the movement of its particles?

The particles gain energy and move faster.
19.

What happens to gas pressure when particles collide more often with the walls of a container?

The gas pressure increases.
20.

What happens during melting?

A solid changes into a liquid as its particles gain energy and can move more freely.
21.

What happens during freezing?

A liquid changes into a solid as its particles lose energy and become fixed in position.
22.

What happens during evaporation?

Some particles at the surface of a liquid gain enough energy to escape as a gas.
23.

What happens during boiling?

A liquid changes into a gas throughout the liquid at its boiling point.
24.

What happens during condensation?

A gas changes into a liquid as its particles lose energy.
25.

How can changes of state be explained using the particle model?

Changes of state happen when particles gain or lose energy, changing how quickly they move and how they are arranged.

Atoms, elements and compounds

1.

What is an atom?

An atom is a tiny particle that makes up an element.
2.

What is Dalton's simple atomic model?

Dalton suggested that matter is made of tiny, solid, indivisible particles called atoms.
3.

What is an element?

An element is a substance made from only one type of atom.
4.

What is a compound?

A compound is a substance made when atoms of two or more different elements are chemically joined.
5.

What is the difference between an atom and an element?

An atom is a single particle, while an element is a substance containing only one type of atom.
6.

What is the difference between an element and a compound?

An element contains one type of atom, while a compound contains atoms of different elements chemically joined together.
7.

What is the difference between a mixture and a compound?

A mixture contains substances that are not chemically joined, while a compound contains elements that are chemically joined.
8.

What are chemical symbols used for?

Chemical symbols are short ways of representing elements.
9.

What does a chemical symbol represent?

A chemical symbol represents an element.
10.

What does a chemical formula represent?

A chemical formula shows which elements are present in a substance and the number of atoms of each element.
11.

How can the formula of a compound show which elements it contains?

The symbols show which elements are present, while the small numbers show how many atoms of each element are present.
12.

What does the formula H₂O tell you about water?

H₂O contains two hydrogen atoms and one oxygen atom.
13.

What does the formula CO₂ tell you about carbon dioxide?

CO₂ contains one carbon atom and two oxygen atoms.
14.

How are atoms arranged in a compound?

Atoms of different elements are chemically joined together in fixed ratios.
15.

What happens to atoms when a compound is formed?

The atoms become chemically joined together in a new substance.
16.

What happens to atoms during a chemical reaction?

Atoms are rearranged to form new substances.
17.

What does conservation of mass mean?

Conservation of mass means that the total mass stays the same during a chemical reaction.
18.

Why is mass conserved during a chemical reaction?

Mass is conserved because atoms are not created or destroyed during a chemical reaction.
19.

What happens to mass during a change of state?

The mass stays the same because the particles are not created or destroyed.
20.

Why does the mass stay the same when a substance changes state?

The particles are simply rearranged or change their movement and arrangement.
21.

How can a chemical reaction change the substances present without changing the total number of atoms?

The atoms are rearranged into new substances, but the total number of each type of atom stays the same.
22.

Why can atoms not simply disappear during a chemical reaction?

Chemical reactions only rearrange atoms; they do not destroy them.
23.

How can chemical formulae be used to represent substances?

Chemical formulae represent substances using chemical symbols and numbers.
24.

How can chemical equations represent chemical reactions?

Chemical equations represent chemical reactions using chemical formulae.
25.

Why must a chemical equation have the same number of each type of atom on both sides?

A chemical equation must have the same number of each type of atom on both sides because atoms are conserved.

Pure and impure substances

1.

What is a pure substance?

A pure substance contains only one substance or one type of particle.
2.

What is a mixture?

A mixture contains two or more substances that are not chemically joined.
3.

What is the difference between a pure substance and a mixture?

A pure substance contains only one substance, while a mixture contains two or more substances.
4.

What happens when a substance dissolves?

Its particles become spread throughout the solvent.
5.

What is a solution?

A solution is a mixture formed when a substance dissolves in a solvent.
6.

What is a solute?

A solute is a substance that dissolves in a solvent.
7.

What is a solvent?

A solvent is a liquid that dissolves a solute.
8.

What happens to particles when a solid dissolves in a liquid?

The solid particles separate and spread between the particles of the liquid.
9.

What is diffusion?

Diffusion is the spreading of particles from an area of higher concentration to an area of lower concentration.
10.

How can diffusion be explained using the particle model?

Diffusion happens because particles move randomly and spread out.
11.

Why do particles spread out during diffusion?

Particles move randomly, causing them to spread from areas where they are more concentrated to areas where they are less concentrated.
12.

How does temperature affect the rate of diffusion?

Increasing temperature usually increases the rate of diffusion because particles move faster.
13.

What is filtration used to separate?

Filtration is used to separate an insoluble solid from a liquid.
14.

How does filtration separate a mixture?

The mixture is passed through a filter; the liquid passes through while the insoluble solid is trapped.
15.

What is evaporation used to separate?

Evaporation can be used to separate a dissolved solid from a solution.
16.

How does evaporation separate a dissolved solid from a solution?

The solvent evaporates, leaving the dissolved solid behind.
17.

What is distillation used to separate?

Distillation is used to separate substances with different boiling points.
18.

How does distillation separate substances in a mixture?

The substance with the lower boiling point evaporates first and is then cooled to form a liquid.
19.

What is chromatography used to separate?

Chromatography is used to separate substances in a mixture, such as different dyes.
20.

How does chromatography separate substances?

Different substances travel at different speeds through the material used for chromatography.
21.

What is a chromatogram?

A chromatogram is the pattern of separated substances produced by chromatography.
22.

How can chromatography be used to identify substances?

A substance can be identified by comparing its position on a chromatogram with known substances.
23.

How can boiling points help identify a pure substance?

A pure substance has a specific boiling point, so its boiling point can be used to help identify it.
24.

How can melting points help identify a pure substance?

A pure substance has a specific melting point, so its melting point can be used to help identify it.
25.

How can physical properties be used to identify whether a substance is pure?

Melting point and boiling point can be compared with known values to help determine whether a substance is pure.

Chemical reactions

Chemical reactions, equations and reaction types

1.

What is a chemical reaction?

A chemical reaction is a process in which one or more substances change into new substances.
2.

What happens to atoms during a chemical reaction?

During a chemical reaction, atoms are rearranged to form new substances.
3.

Why are chemical reactions described as rearrangements of atoms?

The atoms present before the reaction are still present afterwards but joined together differently.
4.

What are reactants?

Reactants are the substances that are present at the start of a chemical reaction.
5.

What are products?

Products are the new substances formed during a chemical reaction.
6.

What is a chemical formula?

A chemical formula shows which elements are present in a substance and the number of atoms of each element.
7.

What is a chemical equation?

A chemical equation represents a chemical reaction using chemical formulae.
8.

How are formulae used to represent chemical reactions?

Formulae are used to show the reactants, products and proportions of substances in a chemical reaction.
9.

What does the arrow in a chemical equation mean?

The arrow means "produces" or "reacts to form".
10.

Why must chemical equations have the same number of each type of atom on both sides?

Chemical equations must have the same number of each type of atom on both sides because atoms are not created or destroyed in a chemical reaction.
11.

Write the word equation for the reaction between magnesium and oxygen.

magnesium + oxygen → magnesium oxide
12.

What is combustion?

Combustion is a reaction in which a substance burns in oxygen.
13.

What substance is needed for combustion to occur?

Oxygen is needed for combustion to occur.
14.

What happens during combustion?

During combustion, a substance reacts with oxygen and releases energy, usually as heat and light.
15.

What is the general word equation for the combustion of a fuel?

fuel + oxygen → carbon dioxide + water
16.

What is thermal decomposition?

Thermal decomposition is the breakdown of a compound into simpler substances when it is heated.
17.

What happens during thermal decomposition?

During thermal decomposition, heat causes one compound to break down into two or more substances.
18.

Write a word equation for a thermal decomposition reaction.

calcium carbonate → calcium oxide + carbon dioxide
19.

What is oxidation?

Oxidation is a reaction in which a substance reacts with oxygen.
20.

What happens when a substance is oxidised?

When a substance is oxidised, it combines with oxygen.
21.

What is a displacement reaction?

A displacement reaction is a reaction in which a more reactive element takes the place of a less reactive element in a compound.
22.

What happens during a displacement reaction?

During a displacement reaction, a more reactive element replaces a less reactive element.
23.

Which metal can displace another metal from a compound?

A metal can displace another metal from a compound if it is more reactive.
24.

How can the reactivity of metals be used to predict a displacement reaction?

If one metal is more reactive than another metal, it can displace the less reactive metal from its compound.
25.

What is the difference between a reactant and a product?

A reactant is a substance used in a reaction, while a product is a new substance formed by the reaction.

Acids, alkalis, salts and catalysts

1.

What is an acid?

An acid is a substance with a pH below 7.
2.

What is an alkali?

An alkali is a soluble substance with a pH above 7.
3.

What is neutralisation?

Neutralisation is a reaction between an acid and an alkali that produces a salt and water.
4.

How can an acid and an alkali be identified using a neutralisation reaction?

An acid and an alkali can be identified by their opposite effects on pH and their ability to react together in neutralisation.
5.

What is the pH scale used to measure?

The pH scale is used to measure how acidic or alkaline a solution is.
6.

What does a pH below 7 show?

A pH below 7 shows that a solution is acidic.
7.

What does a pH of 7 show?

A pH of 7 shows that a solution is neutral.
8.

What does a pH above 7 show?

A pH above 7 shows that a solution is alkaline.
9.

What are indicators used for?

Indicators are used to show whether a solution is acidic, neutral or alkaline.
10.

How can an indicator show whether a solution is acidic or alkaline?

An indicator changes colour depending on the pH of the solution.
11.

What happens when an acid reacts with a metal?

When an acid reacts with a metal, it produces a salt and hydrogen gas.
12.

What two types of products are formed when an acid reacts with a metal?

The two types of products are a salt and hydrogen.
13.

What gas is produced when an acid reacts with a metal?

Hydrogen gas is produced.
14.

How can hydrogen gas be tested for?

Hydrogen can be tested by bringing a lit splint close to the gas; it produces a squeaky pop if hydrogen is present.
15.

Write the general word equation for an acid reacting with a metal.

acid + metal → salt + hydrogen
16.

What is a salt?

A salt is a compound formed when the hydrogen in an acid is replaced by a metal or another positive ion.
17.

What happens when an acid reacts with an alkali?

When an acid reacts with an alkali, they neutralise each other.
18.

What two products are formed when an acid reacts with an alkali?

The two products are a salt and water.
19.

Write the general word equation for a neutralisation reaction.

acid + alkali → salt + water
20.

Why is a reaction between an acid and an alkali called neutralisation?

It is called neutralisation because the acidic and alkaline properties are reduced or cancelled out.
21.

What happens to the pH of an acidic solution when an alkali is added?

Adding an alkali to an acidic solution generally increases its pH towards 7.
22.

What happens to the pH of an alkaline solution when an acid is added?

Adding an acid to an alkaline solution generally decreases its pH towards 7.
23.

What is a catalyst?

A catalyst is a substance that increases the rate of a chemical reaction without being used up.
24.

What does a catalyst do to the rate of a chemical reaction?

A catalyst increases the rate of a chemical reaction.
25.

Is a catalyst used up during a chemical reaction?

No. A catalyst is not used up during the reaction.

Energetics

1.

What is meant by an energy change?

An energy change is the transfer of energy during a process or reaction.
2.

What happens to energy when a substance changes state?

Energy is transferred when particles change their arrangement or movement.
3.

What happens to energy when a solid melts?

Energy is taken in as the particles gain energy and move further apart.
4.

What happens to energy when a liquid boils?

Energy is taken in as particles gain energy and move further apart.
5.

What happens to energy when a gas condenses?

Energy is released as particles lose energy and come closer together.
6.

What happens to energy when a liquid freezes?

Energy is released as particles lose energy and become more closely arranged.
7.

Why do changes of state involve energy changes?

Particles need to gain or lose energy to change their arrangement or movement.
8.

What is an exothermic chemical reaction?

An exothermic reaction is a reaction that transfers energy to the surroundings.
9.

What happens to the surroundings during an exothermic reaction?

The surroundings become warmer.
10.

What is an endothermic chemical reaction?

An endothermic reaction is a reaction that takes in energy from the surroundings.
11.

What happens to the surroundings during an endothermic reaction?

The surroundings become cooler.
12.

How can a temperature change help identify an exothermic reaction?

If the temperature of the surroundings increases, the reaction is likely to be exothermic.
13.

How can a temperature change help identify an endothermic reaction?

If the temperature of the surroundings decreases, the reaction is likely to be endothermic.
14.

What happens to the temperature of the surroundings during an exothermic reaction?

The temperature of the surroundings increases.
15.

What happens to the temperature of the surroundings during an endothermic reaction?

The temperature of the surroundings decreases.
16.

What is the difference between an exothermic and an endothermic reaction?

An exothermic reaction releases energy to the surroundings, while an endothermic reaction takes in energy from the surroundings.
17.

How does an exothermic reaction transfer energy?

Energy is transferred from the reaction to the surroundings.
18.

How does an endothermic reaction transfer energy?

Energy is transferred from the surroundings to the reaction.
19.

Why can changes of state be described as involving energy changes?

Particles must gain or lose energy when their arrangement changes.
20.

What happens to particles when energy is supplied to a substance?

The particles gain energy and usually move faster.
21.

What happens to particles when energy is removed from a substance?

The particles lose energy and usually move more slowly.
22.

How is energy involved when particles change their arrangement?

Energy is transferred as particles change their movement and arrangement.
23.

How can heating cause a change of state?

Heating gives particles more energy, which can cause them to change state.
24.

How can cooling cause a change of state?

Cooling removes energy from particles, which can cause them to change state.
25.

Why are energy changes important when describing chemical reactions and changes of state?

Energy changes help explain how chemical reactions and changes of state happen.

The Periodic Table

1.

What is the Periodic Table?

The Periodic Table is a table that organises all the known elements.
2.

Why are elements arranged in the Periodic Table?

Elements are arranged to show patterns in their properties.
3.

What information does the Periodic Table provide about elements?

It provides information such as the names, symbols and positions of elements.
4.

What is a period in the Periodic Table?

A period is a horizontal row of elements.
5.

What is a group in the Periodic Table?

A group is a vertical column of elements.
6.

What is the difference between a period and a group?

A period is a horizontal row, while a group is a vertical column.
7.

Where are metals generally found in the Periodic Table?

Metals are generally found on the left and in the centre.
8.

Where are non-metals generally found in the Periodic Table?

Non-metals are generally found on the right.
9.

What are physical properties?

Physical properties are properties that can be observed or measured without making a new substance.
10.

What are chemical properties?

Chemical properties describe how a substance reacts with other substances.
11.

Why do different elements have different physical properties?

Their atoms have different structures and arrangements, giving them different properties.
12.

Why do different elements have different chemical properties?

Different elements have different atoms, so they react in different ways.
13.

What was Mendeleev's contribution to the Periodic Table?

Mendeleev developed an early version of the Periodic Table and arranged elements to show patterns in their properties.
14.

How did Mendeleev arrange the elements?

He arranged elements mainly in order of increasing atomic mass, while also considering their properties.
15.

Why did Mendeleev leave gaps in his Periodic Table?

He left gaps where he thought undiscovered elements should fit.
16.

How did Mendeleev use patterns to predict undiscovered elements?

He used patterns in the properties of known elements to predict the properties of undiscovered elements.
17.

How can the position of an element in the Periodic Table help predict its reactions?

Elements in the same group often have similar chemical properties, so position can help predict how an element will react.
18.

What are common physical properties of metals?

Metals are generally shiny, strong, good conductors of heat and electricity, and often have high melting points.
19.

What are common physical properties of non-metals?

Non-metals are generally poor conductors of heat and electricity and often have lower melting points.
20.

How do metals and non-metals differ in their chemical properties?

Metals and non-metals usually react differently and form different types of compounds.
21.

What is a metal oxide?

A metal oxide is a compound formed when a metal reacts with oxygen.
22.

What is a non-metal oxide?

A non-metal oxide is a compound formed when a non-metal reacts with oxygen.
23.

What happens to the acidity of many metal oxides when they react with water?

Many metal oxides form alkaline solutions when they react with water.
24.

What happens to the acidity of many non-metal oxides when they react with water?

Many non-metal oxides form acidic solutions when they react with water.
25.

How can the Periodic Table be used to predict patterns in the properties and reactions of elements?

The Periodic Table shows patterns in element properties, allowing scientists to predict how elements are likely to behave and react.

Materials

1.

What is the reactivity series?

The reactivity series is a list of metals arranged from most reactive to least reactive.
2.

Why are metals placed in a reactivity series?

Metals are placed in a reactivity series so their reactivities can be compared.
3.

Where is carbon placed in the reactivity series?

Carbon is placed between aluminium and zinc in the reactivity series.
4.

Which metals are more reactive than carbon?

Metals such as potassium, sodium, lithium, calcium, magnesium and aluminium are more reactive than carbon.
5.

Which metals are less reactive than carbon?

Metals such as zinc, iron, tin, lead, copper, silver and gold are less reactive than carbon.
6.

What does it mean for a metal to be more reactive than another metal?

A metal is more reactive if it reacts more easily or more vigorously than another metal.
7.

How can the reactivity series be used to compare metals?

The reactivity series shows which metals are more or less reactive than others.
8.

What is a metal oxide?

A metal oxide is a compound made from a metal and oxygen.
9.

How can carbon be used to obtain a metal from its metal oxide?

Carbon can be heated with a metal oxide to remove the oxygen, leaving the metal.
10.

Why can carbon remove some metals from their oxides?

Carbon can remove oxygen from some metal oxides because carbon is more reactive than those metals.
11.

Which metals can be obtained from their oxides using carbon?

Metals below carbon in the reactivity series, such as zinc, iron and lead, can be extracted from their oxides using carbon.
12.

Why can some metals not be obtained from their oxides using carbon?

Metals above carbon are too reactive because they hold onto oxygen more strongly than carbon does.
13.

What are ceramics?

Ceramics are materials made from substances such as clay and are usually produced by heating them.
14.

What are common properties of ceramics?

Ceramics are usually hard, strong, brittle and resistant to high temperatures.
15.

What are polymers?

Polymers are materials made from very long chains of repeating molecules.
16.

What are common properties of polymers?

Polymers are often light, flexible, waterproof and resistant to corrosion.
17.

What are composites?

Composites are materials made by combining two or more different materials.
18.

What is a composite made from?

A composite is made from a matrix material and a reinforcing material.
19.

How can the properties of a composite differ from the materials used to make it?

A composite can have different and improved properties compared with the materials used to make it.
20.

Why are ceramics useful for some applications?

Ceramics are useful because they are hard and can withstand high temperatures.
21.

Why are polymers useful for some applications?

Polymers are useful because they are often light, flexible and resistant to corrosion.
22.

Why are composites useful for some applications?

Composites are useful because they can be strong, light or specially designed for particular uses.
23.

How does the reactivity of a metal affect how it can be obtained from its ore?

The more reactive a metal is, the more difficult it is to extract from its ore.
24.

Why is carbon useful in extracting some metals?

Carbon is useful because it can remove oxygen from the oxides of less reactive metals.
25.

How do ceramics, polymers and composites differ in their properties?

Ceramics are generally hard and brittle, polymers are generally light and flexible, and composites can be designed to have useful combinations of properties.

Earth and atmosphere

1.

What are the main layers that make up the structure of the Earth?

The main layers of the Earth are the crust, mantle, outer core and inner core.
2.

What is the Earth's crust?

The crust is the thin, solid outer layer of the Earth.
3.

What is the Earth's mantle?

The mantle is the thick layer of hot, solid rock beneath the crust.
4.

What is the Earth's outer core?

The outer core is a very hot layer of mainly liquid metal surrounding the inner core.
5.

What is the Earth's inner core?

The inner core is a very hot, solid layer of mainly iron and nickel at the centre of the Earth.
6.

What is the Earth mainly made of?

The Earth is mainly made of rock and metals, including iron and nickel.
7.

What is a rock?

A rock is a naturally occurring solid material made from one or more minerals.
8.

What is the rock cycle?

The rock cycle describes how rocks are continuously changed from one type into another.
9.

How are igneous rocks formed?

Igneous rocks form when molten rock cools and solidifies.
10.

How are sedimentary rocks formed?

Sedimentary rocks form when layers of sediment are deposited, compacted and cemented together.
11.

How are metamorphic rocks formed?

Metamorphic rocks form when existing rocks are changed by heat and pressure.
12.

What is weathering?

Weathering is the breakdown of rocks at or near the Earth's surface.
13.

How can rocks be broken down into smaller pieces?

Rocks can be broken down by water, ice, temperature changes, wind, plants and chemical reactions.
14.

How can sediments become sedimentary rock?

Sediments can become sedimentary rock when they are compacted and cemented together.
15.

How can heat and pressure change existing rocks into metamorphic rocks?

Heat and pressure can change the minerals and structure of existing rocks, forming metamorphic rocks.
16.

What are Earth's natural resources?

Earth's natural resources include rocks, minerals, metals, fossil fuels, water and biological resources.
17.

Why are some of Earth's resources described as limited?

Some resources are limited because they take a very long time to form and can be used faster than they are replaced.
18.

What is recycling?

Recycling is the process of collecting and processing used materials so they can be used again.
19.

How can recycling reduce the use of Earth's limited resources?

Recycling reduces the need to extract new raw materials, helping conserve limited resources.
20.

What is the carbon cycle?

The carbon cycle describes how carbon moves between the atmosphere, living organisms, oceans and rocks.
21.

How is carbon dioxide removed from the atmosphere?

Carbon dioxide is removed from the atmosphere mainly by photosynthesis.
22.

How is carbon dioxide returned to the atmosphere?

Carbon dioxide is returned to the atmosphere by processes such as respiration, combustion and decomposition.
23.

What gases make up most of Earth's atmosphere?

The gases making up most of Earth's atmosphere are nitrogen and oxygen.
24.

How does human activity increase the amount of carbon dioxide in the atmosphere?

Human activities such as burning fossil fuels and deforestation increase the amount of carbon dioxide in the atmosphere.
25.

How can increased carbon dioxide in the atmosphere affect Earth's climate?

Increased carbon dioxide strengthens the greenhouse effect, causing global temperatures to rise and contributing to climate change.