C3.2 Water Hardness

Question 1

Why is rainwater naturally acidic?

Answer 1

Rainwater contains carbonic acid formed where water and carbon dioxide react

Question 2

What is hard water?

Answer 2

Hard water forms when naturally acidic rainwater falls on rocks and minerals and dissolves compounds into the water
usually magnesium and calcium compounds

Question 3

What’s the formula to create soluble calcium hydrogencarbonate?

Answer 3

carbonic acid + calcium carbonate → calcium hydrogencarbonate

Question 4

Which ions make water hard? ;)

Answer 4

Calcium and magnesium ions make water hard when they are present

Question 5

Which hardness of water forms a lather with soap easily?

Answer 5

Soft water

Question 6

How is scum formed?

Answer 6

Scum forms when the dissolved calcium and magnesium ions react with soap and so more soap is needed when using hard water

Question 7

In what regions is water harder?

Answer 7

The midlands / south east

Lincoln, London, Bristol, Southhampton, Brighton

Question 8

Where is water softer?

Answer 8

The north west

Leeds, Manchester, Birmingham
YORKSHIRE, doncaster

Question 9

How can you measure the hardness of water?

Answer 9

You can use TITRATION with a soap solution

The greater the amount of soap solution to form a permanent lather, the harder the water

Question 10

How can you soften temporary hardness?

Answer 10

By boiling the water

Question 11

Why does boiling remove temporary hardness?

Answer 11

Temporary hard water contains dissolved hydrogen carbonate ions.
When boiled, these decompose and form carbonate ions that react with the dissolved magnesium and calcium ions
This forms an insoluble precipitate that can be removed and the hardness is removed

Question 12

What are the benefits of hard water?

Answer 12

• Improved / acquired taste (YORKSHIRE TEA)
• Calcium ions are good for development of bones and teeth
• Can help reduce risk of heart disease

Question 13

What are the drawbacks of Hard water?

Answer 13

• More soap is needed to produce lather, more costs
• The scum produced is unsightly and ruins sexy bath time
• The insoluble precipitate causes limescale that ruins kettles, pipes, etc

Question 14

How can you soften hard water?

Answer 14

By removing the calcium and magnesium ions

Question 15

What are the two methods of softening hard water?

Answer 15

• Adding sodium carbonate

- Ion exchange columns

Question 16

How can you soften hard water by adding sodium carbonate?

Answer 16

Sodium carbonate = washing soda
The insoluble sodium carbonate reacts with the calcium ions to create insoluble precipitates

These precipitates form limescale :(

Question 17

How can you soften water using ion exchange columns?

Answer 17

Bead ion exchange resins are packed into an ion exchange column
The beads have sodium ions attached, these are swapped for calcium and magnesium ions as the water passes through
The water now doesn’t contain calciium or magnesium ions

It can become saturated with magnesium and calcium ions and so it needs to be regenerated by adding sodium chloride

Convenient + cost effective

Question 18

How are ion exchange columns used commercially?

Answer 18

Dishwashers

Question 19

In what ways is water purified?

Answer 19

• Adding fluoride
• Filtered (improve quality + taste)
• Distilled ( sea water to drinking water)

Question 20

How is drinking water of sufficient quality produced?

Answer 20

• Supplied from an appropriate source
• Filtered
• Chlorinated

Question 21

Where are appropriate sources of water?

Answer 21

Lakes, Rivers, Aquifers, Reservoirs

Question 22

What is an aquifer?

Answer 22

An aquifer is an underground layer of permeable rock, gravel or sand that is soaked with water

Question 23

After filtration, what occurs to water in a sedimentation tank?

Answer 23

Aluminium sulphate is added in order to clump together the tiny particles that were too fine for the filtration
The mixture is then passed through another fine filter system

Question 24

How can you remove microbes from water?

eg disease causing microbes such as Typhoid and cholera

Answer 24

Chlorine kills microbes in the water

Question 25

What are the benefits of adding fluoride to the water supply?

Answer 25

Improved dental health by reducing tooth decay

Question 26

Why would people not want fluoride added to the water supply?

Answer 26

• It has been linked to tooth staining and bone disease

- Doesn’t allow people to have the choice of if they want it or not (unethical)

Question 27

What do filter cartridges in a commercial / at home filtering device contain?

Answer 27

• Silver to kill bacteria
• Carbon to absorb impurities (eg chlorine)
• Ion exchange resins to soften water

Question 28

How can salt water be made safe to drink?

Answer 28

DISTILLATION

Salt water is boiled, the condensation is cooled and collected

(salt is removed)

Question 29

What are the disadvantages of distillation?

Answer 29

• Expensive due to needing a lot of energy
• Uses fossil fuels
• Carbon dioxide contributes to global warming

Question 30

Why is distillation common in the middle east?

Answer 30

There is little rainfall but the countries are wealthy due to oil supplies

Question 31

How can you test the purity of water?

Answer 31

Measuring its boiling point ( 100 = pure)
Evaporating it ( No salt etc left = pure)