Pure substances

Substances can exist in different states of matter.

The states of matter are solid, liquid and gas.

A substance has a melting point of – 7 °C and a boiling point of 59 °C.

A student purified a sample of water by distillation.

Figure 1 shows the apparatus.

Name the processes occurring at A, B, and C in Figure 1.

Choose answers from the box.

A

B

C

The student wanted to collect as much pure water as possible from the sample.

Some water was lost as steam from the end of the delivery tube.

Suggest one improvement to the apparatus to change more of the steam to water.

The water collected in the test tube is pure water.

Which statement is true for pure water?

Tick () one box.

Pure water boils at exactly 100 °C.

Pure water contains only one type of atom.

Pure water has a range of pH values.

Which two of the following are pure substances in chemistry?

Tick () two boxes.

Air

Carbon dioxide

Crude oil

Oxygen

Salt solution

This question is about atoms.

Complete Figure 9 to represent this atom of lithium.

You should draw and label the sub-atomic particles.

Scientific models of the atom have included: the Dalton atom

the plum pudding model

the nuclear atom.

Explain why the model of the atom has changed over time.

You should refer to these three models.

An atom has a radius of 0.348 nm.

Calculate the radius of the atom in metres.

Give your answer in standard form.

In chemistry, a pure substance is a single element or compound.

Describe how measurements taken during a change of state can show if a substance is pure.

Different substances change state at different temperatures.

Table 1 shows the melting points and boiling points of three substances.

What is the state of sodium at 90 °C?

Tick (✓) one box.

Gas

Liquid

Solid

Complete the sentence.

Choose the answer from the box.

Sodium chloride is a liquid at ___________________ °C.

A student investigated the boiling point of different concentrations of sodium chloride solutions.

Figure 3 shows the apparatus.

This is the method used.

1. Add 100 cm³ of water to a beaker.

2. Add 10 g of sodium chloride to the water.

3. Heat the beaker until the solution boils.

4. Record the boiling point of the solution.

5. Repeat steps 1 to 4 with different masses of sodium chloride.

Figure 4 shows the results.

Determine the difference between the boiling point of the solution using:

and

Use Figure 4.

Boiling point using 15 g of sodium chloride ________________ °C

Boiling point using 30 g of sodium chloride ________________ °C

Describe the pattern of the results in Figure 4.

Include data from Figure 4 in your answer.

The student heated water at its boiling point until all the liquid water changed to water vapour.

mass of water = 0.20 kg specific latent heat of vaporisation of water = 2 260 000 J/kg

Calculate the energy required to change the liquid water into water vapour.

Use the equation:

energy for the change of state = mass × specific latent heat of vaporisation

Choose the unit from the box.

Boiling water can be used to cook food.

Food can be cooked in a pressure cooker.

Figure 5 shows a pressure cooker.

What will happen to the water particles as the temperature of the water increases?

Tick (✓) one box.

The kinetic energy of the particles will decrease.

The particles will hit each other less often.

The particles will move faster.

The pressure inside the pressure cooker changes during heating.

Table 2 shows the boiling point of the water in the pressure cooker at different pressures.

What happens to the boiling point of the water as the pressure in the pressure cooker increases?

Use Table 2.

Figure 6 shows a saucepan.

The boiling point of water in a saucepan is 100 °C.

Explain one advantage of using a pressure cooker instead of a saucepan to cook food.

This question is about solids and liquids.

Describe two ways the arrangement of particles in a solid is different from the arrangement of particles in a liquid.

You should answer in terms of the particle model.

Liquid water can freeze to form solid ice.

Grit is spread on roads to reduce the formation of ice.

Grit contains a mixture of salt and sand.

Explain why less ice is formed when salt is spread on roads.

Figure 10 shows the mass of ice melted by 1 kg of grit at different temperatures.

Draw a line of best fit on Figure 10.

Predict the mass of ice that 1 kg of grit would melt at −20 °C

Use Figure 10.

Describe the effect of changing temperature on the mass of ice that 1 kg of grit can melt.

Use Figure 10.

Grit is spread on roads when low temperatures are expected.

Some roads are built with temperature sensors in the surface.

The sensors indicate when to spread grit on the roads.

Suggest one advantage of having temperature sensors in roads rather than relying on weather forecasts.

This question is about solids and liquids.

Describe two ways the arrangement of particles in a solid is different from the arrangement of particles in a liquid.

You should answer in terms of the particle model.

Liquid water can freeze to form solid ice.

Grit is spread on roads to reduce the formation of ice.

Grit contains a mixture of salt and sand.

Explain why less ice is formed when salt is spread on roads.

Figure 1 shows the mass of ice melted by 1 kg of grit at different temperatures.

Draw a line of best fit on Figure 1.

Predict the mass of ice that 1 kg of grit would melt at −20 °C

Use Figure 1.

Describe the effect of changing temperature on the mass of ice that 1 kg of grit can melt.

Use Figure 1.

Grit is spread on roads when low temperatures are expected.

Some roads are built with temperature sensors in the surface.

The sensors indicate when to spread grit on the roads.

Suggest one advantage of having temperature sensors in roads rather than relying on weather forecasts.

Water is cycled through the environment.

Rain provides fresh water.

Fresh water in the ground contains small amounts of dissolved substances.

Suggest one source of these dissolved substances.

Figure 5 shows the total monthly rainfall from November 2017 to October 2018 in the UK.

Give two conclusions you can make from the data shown in Figure 5.

Determine the percentage increase in rainfall in the month of January 2018 compared to the month of November 2017.

Suggest one reason why scientists cannot accurately predict the total rainfall in the UK for November 2020.

A student produced distilled water from fresh water.

Figure 6 shows the apparatus used.

The student stated that the thermometer measured the boiling point of water.

The reading on the thermometer was 102 ºC

Describe how the apparatus can be changed to obtain the correct value for the boiling point of water.

Give one reason why the change is needed to obtain the correct value.

The student collected less distilled water than expected from a sample of fresh water.

Suggest one change to the apparatus to increase the volume of distilled water collected from the fresh water sample.

Give one reason why this suggestion would increase the volume of distilled water collected.

Sea water in some parts of the world is used to produce potable water.

Distillation can be used to desalinate sea water.

Explain one disadvantage of using distillation to obtain potable water.

Name one other method used for desalination.

Do not refer to distillation in your answer.