Potable water

A student investigated the mass of dissolved solids in sea water.

This is the method used.

1. Weigh an empty evaporating basin.

2. Measure 10.0 cm³ of sea water sample A into the evaporating basin using a burette.

3. Heat the evaporating basin until all the water seems to have evaporated.

4. Weigh the evaporating basin and contents.

5. Calculate the mass of dissolved solids in the sample.

6. Repeat steps 1 to 5 with sea water samples B, C and D.

Why did the student use a burette rather than a measuring cylinder to measure

What was the dependent variable in this investigation?

Describe how the student could make sure all of the water had evaporated in step 3.

How did the student calculate the mass of dissolved solids in each sea water sample?

Table 3 shows the results.

Calculate the mean concentration of dissolved solids in 10.0 cm³ samples of sea water A, B, C and D.

Use Table 3 and the equation:

Suggest why sea water samples A, B, C and D contain different masses of dissolved solids.

A student investigated the mass of dissolved solids in sea water.

This is the method used.

1. Weigh an empty evaporating basin.

2. Measure 10.0 cm³ of sea water sample A into the evaporating basin using a burette.

3. Heat the evaporating basin until all the water seems to have evaporated.

4. Weigh the evaporating basin and contents.

5. Calculate the mass of dissolved solids in the sample.

6. Repeat steps 1 to 5 with sea water samples B, C and D.

Why did the student use a burette rather than a measuring cylinder to measure

What was the dependent variable in this investigation?

Describe how the student could make sure all of the water had evaporated in step 3.

How did the student calculate the mass of dissolved solids in each sea water sample?

Table 1 shows the results.

Calculate the mean concentration of dissolved solids in 10.0 cm³ samples of sea water A, B, C and D.

Use Table 1 and the equation:

Suggest why sea water samples A, B, C and D contain different masses of dissolved solids.

This question is about water.

Hydrogen gas reacts with oxygen gas to produce water.

Water is decomposed into hydrogen gas and oxygen gas using electricity.

Which two words describe the reaction between hydrogen gas and oxygen gas?

Tick (✓) two boxes.

Water molecules break down into hydrogen ions and hydroxide ions.

The equation for the reaction is:

Which sentence describes this reaction at equilibrium?

Tick (✓) one box.

Water collected from rivers is used in the home for drinking and flushing toilets.

Water used in the home must be potable.

Potable water is safe to drink.

Waste water produced after use in the home is called sewage.

Figure 3 shows how water is collected from rivers and returned to rivers after use.

Explain what happens to water in Process A and in Process B in Figure 3.

Do not refer to use of water in the home.

This question is about water.

Sewage is waste water. Sewage contains organic matter.

Describe how sewage is treated to remove organic matter.

Sea water and ground water are treated to make them potable. Table 5 shows information about the composition and treatment of sea water and of ground water.

Sea water is desalinated during Process 1. Which pair of concentrations could represent X in Table 5 ? Tick (✓) one box.

Explain why the concentrations of sodium ions and of chloride ions in the ground water in Table 5 are unchanged by Process 1.

Explain why the ground water in Table 5 requires Process 2 before the water is safe to drink.

After treatment the ground water in Table 5 is sold by a company as pure water. The ground water in Table 5 is not chemically pure because the water contains sodium ions and chloride ions.

Suggest what the company means by ‘pure’.

Chlorine is also used to treat some ground water. Describe the test for chlorine gas. Give the result of the test.

This question is about water.

A student investigated the concentration of salt in sea water.

This is the method used.

1. Filter the sea water to remove sand.

2. Measure the mass of an empty evaporating dish.

3. Measure 50 cm³ of sea water into the evaporating dish.

4. Heat the evaporating dish and sea water.

5. Evaporate the sea water to dryness.

6. Measure the mass of the evaporating dish and salt.

What equipment should the student use to measure:

• the mass of the evaporating dish

• the volume of sea water?

Mass of evaporating dish

Volume of sea water

Table 2 shows the student’s results.

The student used 50 cm³ of sea water.

Calculate the mass of salt in 1000 cm³ of this sea water.

The salt must be completely dry.

Which two extra steps are needed to show that the salt is completely dry?

Tick (✓) two boxes.

Two students, Y and Z, distil sea water to collect water.

Figure 1 shows the apparatus used by each student to collect the water.

Students Y and Z boil the same volume of sea water for the same period of time.

Explain why student Y collects a smaller volume of water than student Z.

Water obtained by distillation does not need to be sterilised and is safe to drink.

Suggest why.

Fresh water needs to be sterilised before it is safe to drink.

How is fresh water sterilised?

Tick (✓) two boxes.

A student tests the pH of fresh water using universal indicator solution.

When added to the fresh water, the colour of the universal indicator solution is green.

What is the pH of this fresh water?

This question is about water.

In the UK, potable (drinking) water is produced from different sources of fresh water.

Explain how potable water is produced from fresh water.

A different country has:

• very little rainfall

• a long coastline

• plentiful energy supplies.

Suggest one process this country could use to obtain most of its potable water.

Waste water is not fit to drink.

Treatment of waste water produces two substances:

• liquid effluent

• solid sewage sludge.

Draw one line from each substance to the way the substance is processed.

Substance Process

Table 6 shows information about the disposal of processed solid sewage sludge in the UK in 1992 and in 2010.

Calculate the percentage of processed solid sewage sludge that was burned in 2010.

Give your answer to 3 significant figures.

Use Table 6.

Suggest one reason why the total mass of processed solid sewage sludge increased between 1992 and 2010.

Between 1992 and 2010 the proportion of processed solid sewage sludge used as fertiliser increased.

Suggest two reasons why.

This question is about water.

In the UK, potable (drinking) water is produced from different sources of fresh water. Explain how potable water is produced from fresh water.

A different country has:

• very little rainfall

• a long coastline

• plentiful energy supplies.

Suggest one process this country could use to obtain most of its potable water.

Waste water is not fit to drink. Treatment of waste water produces two substances:

• liquid effluent

• solid sewage sludge.

Draw one line from each substance to the way the substance is processed.

Substance Process

Table 1 shows information about the disposal of processed solid sewage sludge in the UK in 1992 and in 2010.

Calculate the percentage of processed solid sewage sludge that was burned in 2010. Give your answer to 3 significant figures. Use Table 1.

Suggest one reason why the total mass of processed solid sewage sludge increased between 1992 and 2010.

Between 1992 and 2010 the proportion of processed solid sewage sludge used as fertiliser increased. Suggest two reasons why.

This question is about drinking water.

There are two main steps in producing drinking water from fresh water.

Draw one line from each step to the reason for the step.

Which two substances are used to sterilise fresh water?

Tick (✓) two boxes.

A large amount of aluminium sulfate was accidentally added to the drinking water supply at a water treatment works.

Scientists tested a sample of the drinking water to show that it contained dissolved solids.

Which two methods show the presence of dissolved solids in the sample of drinking water?

Tick (✓) two boxes.

Scientists tested two water samples from the drinking water supply.

The scientists tested one sample for aluminium ions and the other sample for sulfate ions.

Draw one line from each ion to the compound needed to identify the ion.

How could pure water be produced from drinking water that contained dissolved solids?

Tick (✓) one box.

A large amount of aluminium sulfate was accidentally added to the drinking water supply at a water treatment works.

Describe a test to show that the drinking water contained aluminium ions.

Give the result of the test.

Describe a test to show that the drinking water contained sulfate ions.

Give the result of the test.

Plan an investigation to find the total mass of dissolved solids in a 100 cm³ sample of the drinking water.

Your investigation should produce valid results.