2.7 - Water

Question 1

How to test between hard and soft water

Answer 1

• place water in a boiling tube
• add soap solution and shake to see if a lather forms within 30 seconds
• if no lather forms keep shaking
• soft water needs a little soap to form lather whereas hard water needs a lot

Question 2

Advantages of living in a hard water area

Answer 2

• strengthens teeth and bones

- reduces heart disease

Question 3

Disadvantages of living in a hard water area

Answer 3

• limescale

- blocks pipes

Question 4

Describe the stages in purifying water

Answer 4

• sedimentation where the larger solid particles settle at the bottom
• filtration where the water is extracted from the reservoir and is filtered to remove smaller particles
• chlorination where the bacteria is not removed through filtration so chlorine is added to the water to kill bacteria

Question 5

Uses of water

Answer 5

• for factories in cooling machinery
• hygiene
• farms to grow food
• drinking water

Question 6

How can we decrease water use?

Answer 6

• use washing machines and dish washers only when full
• have showers
• repair dripping taps
• use waste water for washing cars
• don’t let water to run excessively

Question 7

Describe desalination

Answer 7

• process that removes minerals from salt water

- boiling is used but there has to be a nearby sea and it is costly

Question 8

Explain chromotography

Answer 8

• to separate pigments in ink
• spots of colours are placed on pencil line
• dish of water (solvent) is raised until the paper comes into contact with the water surface
• the chromotogram develops
• most soluble substance travels the furthest

Question 9

Explain gas chromotography

Answer 9

Can give the amount of substance present

-use this method to identify the amount of pollutant in the air or illegal drug in blood

Question 10

How does temperature affect solubility

Answer 10

The higher the temp, the more solute will dissolve until a saturated solution forms (solution that cannot dissolve anymore solute into it)

Question 11

Describe sedimentation

Answer 11

Where the larger solid particles will settle to the bottom

Question 12

Describe filtration

Answer 12

Where the water is extracted from the reservoir, and is filtered to remove smaller particles

Question 13

Describe chlorination

Answer 13

Where because the bacteria is not removed through filtration, chlorine is added to the water to kill the bactiera

Question 14

Explain distillation with ethanol

Answer 14

• separates water and miscible liquids
• ethanol boils at 78C and water and ethanol are miscible
• in a mixture of ethanol and water, the ethanol would boil and evaporate first( lower boiling point) leaving water behind
• would condense on the cold wall of the condenser

Question 15

Why is some water hard?

Answer 15

From rainwater passing along limestone, calcium ions will collect in the water. Ions such as magnesium ions will also collect in the water which makes the water hard

Question 16

How to use soap to tell of water is hard or soft

Answer 16

Soap in hard water does not readily lather but scum is formed

Question 17

Advantages and disadvantages of hard water

Answer 17

Ad: - strengthens teeth

• reduces risk of heart disease
• some people prefer the taste

Dos: -more soap is needed

• limescale can make them less efficient at boiling water
• hot water pipes can be blocked up with limescale

Question 18

dis of desalination

Answer 18

• uses lots of energy
• expensive
• plants produce greenhouse gases

Question 19

Describe an experiment to see if hard or soft water forms

Answer 19

• place 10cm of water in boiling tube
• add 0.5cm of soap solution and shake for 10 seconds to see if a lather forms that lasts 30 seconds
• if no lather forms add more soap
• record the volume needed to form a soap

Question 20

Difference between hard and soft water

Answer 20

Soft- no Ca or Mg ions present

Hard- Ca or Mg ions present

Question 21

Experiment to see if water is permanently hard or temporarily

Answer 21

• boil samples

- if the water is still difficult to lather then it is permanently hard

Question 22

What compound does temporary hard water have that permanently doesnt

Answer 22

Hydrogencarbonate

Question 23

How to remove permanent hardness by washing soda

Answer 23

1. Add sodium carbonate (washing soda) which produces calcium carbonate so the calcium ions are removed as solid CaCo3 making thw water softer

Question 24

How does an ion exchange column remove hardness in water?

Answer 24

-when the hard water is passed along negatively charged particles in the container, the positive ions of magnesium and calcium are attracted and are held there and are replaced with sodium ions, so the water leaves the container soft

Question 25

Disadvantages of ion exchange column

Answer 25

• bacteria contamination
• iron fouling
• chlorine contamination

Question 26

Ad and dis of boiling, washing soda, ion exchane

Answer 26

Boiling: ad- no expensive equip needed, dis- forms limescale
Washing soda- can do both hardness types but produces scum
Ion exchange- works for both hardness but needs to recharge