Potable water

Humans use many different resources.

Water is an important natural resource.

What is meant by ‘potable water’?

Tick () one box.

Waste water needs treatment before the water is put back into rivers and the sea.

The first stage of waste water treatment is to pass the waste water through metal grids.

Why is the waste water passed through metal grids?

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Clothes can be made from different materials.

Some clothes are made from wool and some clothes are made from poly(propene).

One sheep produces 4.5 kg of wool.

50 g of wool is needed to make a hat.

Calculate the number of hats that can be made from the wool of one sheep.

1 kg = 1000 g

Table 4 gives information about poly(propene) and wool.

Explain the advantages of using poly(propene) and of using wool for clothing.

After being used, clothes can be:

• given to other people to wear

• used to make insulation blocks for buildings.

Complete the sentences.

Choose answers from the box.

When clothes are given to other people to wear,

When clothes are used to make insulation blocks for buildings,

Poly(propene) is made from an alkene.

Alkenes are produced by cracking alkanes.

A high temperature is used for cracking alkanes.

Which two of the following can also be used to crack alkanes?

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Which chemical is used to test for alkenes?

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Tap water must be safe to drink.

What name is given to water that is safe to drink?

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Water is sterilised to make the water safe to drink.

Which two of the following are used to sterilise drinking water?

Tick () two boxes.

A student investigated the mass of dissolved solids in samples of river water,

sea water and tap water.

This is the method used.

1. Weigh an evaporating basin.

2. Measure 100 cm³ of river water.

3. Pour the river water into the evaporating basin.

4. Heat the evaporating basin until all the water has evaporated.

5. Weigh the evaporating basin and dissolved solids.

6. Calculate the mass of dissolved solids in the water.

7. Repeat steps 1 to 6 with sea water and then with tap water.

Which is the most suitable equipment to measure 100 cm³ of water?

Tick () one box.

Table 3 shows the results.

Calculate value X in Table 3.

Identify the variables used in the investigation.

Draw one line from each variable to the example of the variable.

Table 4 shows the mass of different types of ions dissolved

in 1 dm³ of sea water.

Complete Figure 3.

You should:

complete the scale for the y-axis

plot the data from Table 4 as a bar chart.

The Earth’s natural resources are used to manufacture useful products.

One useful product is potable water.

Potable water can be produced from sea water by distillation.

Give one disadvantage of using distillation to produce potable water.

Describe one other method to produce potable water from sea water.

A student investigated the mass of dissolved solids in a 100 cm³ sample of

sea water.

This is the method used.

1. Weigh an evaporating basin.

2. Measure 100 cm³ of sea water.

3. Pour the sea water into the evaporating basin.

4. Heat the evaporating basin.

5. Weigh the evaporating basin and contents.

6. Calculate the mass of dissolved solids in the sea water.

Explain how repeating steps 4 and 5 would improve this method.

The total mass of dissolved solids in a 100 cm³ sample of sea water is 3.50 g.

The percentage of sodium chloride in the dissolved solids is 77.8%.

Calculate the mass of sodium chloride dissolved in the 100 cm³ sample of sea water.

Biological methods are used to extract metal compounds from metal ores.

One method of producing copper from low-grade copper ores is by using bacteria.

The bacteria produce leachate solutions that contain copper compounds.

Give two methods that can be used to extract copper from these leachate solutions.

Phytomining uses plants to absorb metal compounds from low-grade ores.

Describe how the metal compounds are obtained from the plants.

Nickel is produced by phytomining.

One hectare of plants produces 215 kg of nickel.

Determine the area required to produce 750 kg of nickel.

Give your answer in m².

Some types of water contain dissolved substances.

A student investigated the mass of dissolved solids in distilled water and in sea water. Figure 5 shows the apparatus.

This is the method used.

1. Weigh an evaporating basin.

2. Add a sample of distilled water to the evaporating basin.

3. Weigh the evaporating basin and the water sample.

4. Heat the water sample.

5. Weigh the evaporating basin and contents.

6. Repeat steps 1 to 5 two more times.

7. Repeat steps 1 to 6 with sea water.

Give one safety precaution the student should take.

The method used did not give valid results. Which two improvements could the student make to give valid results? Tick (✓) two boxes.

A different student used a method which gave valid results. Table 2 shows the results.

The student concludes that distilled water is pure. Suggest one reason why.

Tap water is potable. One step in producing potable water is sterilisation.

Why is potable water sterilised?

Tick (✓) one box.

Chlorine is used to sterilise water. The reaction between chlorine and water is reversible. Complete the sentence.

Equilibrium is reached when the forward and reverse reactions

The test for chlorine uses damp litmus paper. Complete the sentence. Choose the answer from the box.

When damp litmus paper is put into chlorine gas

There is evidence that adding fluoride ions to drinking water reduces tooth decay.

Figure 6 shows the percentage of people showing tooth decay.

Compare the effects of adding fluoride ions to drinking water on tooth decay in people between the ages of 25 and 74. Use data from Figure 6.

Student A says that water companies should add fluoride ions to all drinking water. Student B disagrees. Suggest one reason why Student B may think that fluoride ions should not be added to all drinking water.

Some types of water contain dissolved substances.

A student investigated the mass of dissolved solids in distilled water and in sea water. Figure 1 shows the apparatus.

This is the method used.

1. Weigh an evaporating basin.

2. Add 20 cm³ of distilled water to the evaporating basin.

3. Weigh the evaporating basin and the water sample.

4. Heat the water sample for 2 minutes.

5. Weigh the evaporating basin and contents.

6. Repeat steps 1 to 5 two more times.

7. Repeat steps 1 to 6 with sea water.

The method used by the student did not give valid results. Describe one improvement the student could make to obtain valid results.

A different student used a method which gave valid results.

Table 2 shows the results.

Calculate the value X for the mass of dissolved solids in sea water in Test 2.

The student concludes that distilled water is pure. Describe a test to confirm that distilled water is pure.

Tap water is potable.

A stage in the production of potable water is sterilising. A gas is used to sterilise water. The equation for the reaction is:

What is meant by the symbol ?

The reaction is at equilibrium. The reaction is exothermic. What happens to the equilibrium position when the temperature is increased? Tick (✓) one box.

Describe a test to identify the gas used to sterilise water.

Another stage in the production of potable water is filtering. Explain why potable water contains dissolved solids after filtering.

Water that is safe to drink is called potable water.

Compare how easily potable water can be obtained from:

• waste water (sewage)

• ground water (fresh water).

A scientist produced potable water from 150 cm³ of salty water.

Which process can be used to produce potable water from salty water?

Tick (✓) one box.

The salty water contains sodium chloride.

The scientist collected 2.40 g of sodium chloride from 150 cm³ of salty water.

Calculate the concentration of sodium chloride in grams per dm³

Water that is safe to drink is called potable water. Compare how easily potable water can be obtained from:

• waste water (sewage)

• ground water (fresh water).

A scientist produced potable water from 150 cm³ of salty water.

Which process can be used to produce potable water from salty water? Tick (✓) one box.

The salty water contains sodium chloride. The scientist collected 2.40 g of sodium chloride from 150 cm³ of salty water. Calculate the concentration of sodium chloride in grams per dm³

Fresh water contains low levels of dissolved salts.

Water reacts with anhydrous copper sulfate in a reversible reaction.

The word equation for the reaction is: water + anhydrous copper sulfate hydrated copper sulfate

How does the equation show that the reaction is reversible?

Complete the sentences. Choose answers from the box.

Figure 1 shows anhydrous copper sulfate in a sealed container.

Suggest one reason why anhydrous copper sulfate is kept in a sealed container.

Sodium chloride dissolves in water to form sodium chloride solution.

Draw one line from each substance to the description of the substance. Substance Description of substance

Name the process used to obtain solid sodium chloride from sodium chloride solution.

Two processes used to obtain potable water from fresh water are:

• filtering

• sterilising.

Give one reason why each process is used.

Which type of water is the easiest to obtain potable water from? Tick (✓) one box.

Which of the following is the first stage of waste water treatment? Tick (✓) one box.

The methods used to produce potable water depend upon available sources of water.

Suggest how copper sulfate can be used as a test for the presence of water.

The boiling point is used to check the purity of a sample of water.

In chemistry, what is meant by a ‘pure substance’?

The boiling point of a 250 g sample of water was 100.60 °C.

The boiling point of pure water in a data book is 100.00 °C.

Each 1% of impurity increases the boiling point of water by 0.12 °C.

Calculate the mass of the impurity in the sample of water.

Explain how distillation is used to obtain potable water from salty water.

Obtaining potable water from salty water is more expensive than obtaining potable water from ground water.

Explain why.

Refer to the processes used in both methods in your answer.

A student investigated the mass of dissolved solids in water samples. Figure 4 shows the apparatus used.

This is the method used.

1. Record the mass of a dry evaporating basin.

2. Pour 25 cm³ of the water sample into the evaporating basin.

3. Place the evaporating basin on the beaker for 10 minutes.

4. Record the mass of the evaporating basin and contents.

What is used to find the mass of the evaporating basin? Tick (✓) one box.

One error is that droplets of water collect on the bottom of the evaporating basin.

Suggest how this error affects the mass of the evaporating basin and contents.

How can this error be corrected?

Another error in the method is that not all the water was removed from the water sample. How can this error be corrected? Tick (✓) one box.

The water in the water sample turns into steam. What is the name of this process?

Another student did the experiment correctly with three water samples A, B and C. Table 2 shows the results.

The range is the difference between the largest value and the smallest value. Which water sample has the greatest range of results? Tick (✓) one box.

Calculate the mean mass X for water sample A. Use Table 2.

What is the dependent variable in this experiment? Tick (✓) one box.

A different water sample contains 3.6 g of dissolved solids in 150 cm³ Calculate the mass of dissolved solids in 25 cm³ of this sample.

A student investigated the mass of dissolved solids in four water samples A, B, C and D. Figure 4 shows the apparatus used.

This is the method used.

1. Record the mass of a dry evaporating basin.

2. Pour 25 cm³ of water sample A into the evaporating basin.

3. Place the evaporating basin on the beaker for 10 minutes.

4. Record the mass of the evaporating basin and contents.

5. Repeat steps 1 to 4 with water sample A three more times.

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

What type of variable is the mass of dissolved solids? Tick (✓) one box.

The method produced an error in the mass recorded in step 4. Suggest what caused the error. How could the error be avoided?

Another student carried out the investigation correctly.

Table 1 shows the results.

Calculate value X in Table 1.

Which water sample has the greatest range of masses of dissolved solids? Give the reason for your answer.

Water companies measure the volume of water used by households in

25 cm³ of a different water sample contained 0.016 g of dissolved solids. Calculate the mass of dissolved solid in 1 m³ of this water sample.

Give your answer in standard form.

Mass (in standard form) = g

Water that is safe to drink contains dissolved substances.

What do we call water that is safe to drink?

Tick (✓) one box.

Describe a test for pure water.

Give the result of the test if the water is pure.

Describe a method to determine the mass of dissolved solids in a 100 cm³ sample of river water.

A sample of river water contains 125 mg per dm³ of dissolved solids.

Calculate the mass of dissolved solids in grams in 250 cm³ of this sample of river water.

Give your answer to 2 significant figures.

A water company allows a maximum of 500 mg per dm³ of sulfate ions in drinking water.

A sample of drinking water contains 44 mg per dm³ of sulfate ions.

Calculate the percentage (%) of the maximum allowed mass of sulfate ions in the sample of drinking water.

Water that is safe to drink contains dissolved substances.

What do we call water that is safe to drink? Tick (✓) one box.

Describe a test for pure water. Give the result of the test if the water is pure.

Describe a method to determine the mass of dissolved solids in a 100 cm³ sample of river water.

A sample of river water contains 125 mg per dm³ of dissolved solids. Calculate the mass of dissolved solids in grams in 250 cm³ of this sample of river water. Give your answer to 2 significant figures.

A water company allows a maximum of 500 mg per dm³ of sulfate ions in drinking water. A sample of drinking water contains 44 mg per dm³ of sulfate ions. Calculate the percentage (%) of the maximum allowed mass of sulfate ions in the sample of drinking water.

A student tested a sea water sample for dissolved solids.

Figure 6 shows the apparatus.

What is apparatus X on Figure 6 ?

Tick one box.

The student did the test four times. The student calculated the mass of solid on apparatus X after heating.

Table 3 shows the student’s results.

Calculate the mean mass of solid.

Do not include the anomalous result in your calculation.

Give your answer to 2 significant figures.

The student distilled a sample of sea water in the apparatus shown in Figure 7

What change of state is happening at the surface of the sea water in Figure 7 ?

Describe how the water in the test tube in Figure 7 is different from the sea water.

Why does producing drinking water from sea water using distillation cost a lot of money?

River water is filtered then sterilised to make drinking water.

Why are these two processes done?

A student investigated the mass of dissolved solids in 5 cm³ samples of water. Figure 3 shows the apparatus.

Table 2 shows the student’s results.

Calculate mass X in Table 2

5 cm³ is a small volume of water for each experiment. Give one advantage and one disadvantage of using a larger volume.

Potable water is not pure water. Describe the difference between potable water and pure water.

Potable water is obtained from both groundwater and from sea water. Describe how groundwater and sea water are treated to produce potable water.

The percentage by mass of dissolved solids in a 6.50 g sample is 2.2% Calculate the mass of the dissolved solids.