C3.2 Water Hardness Flashcards Preview

Chemistry > C3.2 Water Hardness > Flashcards

Flashcards in C3.2 Water Hardness Deck (31):
1

Why is rainwater naturally acidic?

Rainwater contains carbonic acid formed where water and carbon dioxide react

2

What is hard water?

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

3

What's the formula to create soluble calcium hydrogencarbonate?

carbonic acid + calcium carbonate → calcium hydrogencarbonate

4

Which ions make water hard? ;)

Calcium and magnesium ions make water hard when they are present

5

Which hardness of water forms a lather with soap easily?

Soft water

6

How is scum formed?

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

7

In what regions is water harder?

The midlands / south east

Lincoln, London, Bristol, Southhampton, Brighton

8

Where is water softer?

The north west

Leeds, Manchester, Birmingham
YORKSHIRE, doncaster

9

How can you measure the hardness of water?

You can use TITRATION with a soap solution
The greater the amount of soap solution to form a permanent lather, the harder the water

10

How can you soften temporary hardness?

By boiling the water

11

Why does boiling remove temporary hardness?

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

12

What are the benefits of hard water?

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

13

What are the drawbacks of Hard water?

- 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

14

How can you soften hard water?

By removing the calcium and magnesium ions

15

What are the two methods of softening hard water?

- Adding sodium carbonate
- Ion exchange columns

16

How can you soften hard water by adding sodium carbonate?

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

These precipitates form limescale :(

17

How can you soften water using ion exchange columns?

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

18

How are ion exchange columns used commercially?

Dishwashers

19

In what ways is water purified?

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

20

How is drinking water of sufficient quality produced?

- Supplied from an appropriate source
- Filtered
- Chlorinated

21

Where are appropriate sources of water?

Lakes, Rivers, Aquifers, Reservoirs

22

What is an aquifer?

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

23

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

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

24

How can you remove microbes from water?

eg disease causing microbes such as Typhoid and cholera

Chlorine kills microbes in the water

25

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

Improved dental health by reducing tooth decay

26

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

-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)

27

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

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

28

How can salt water be made safe to drink?

DISTILLATION

Salt water is boiled, the condensation is cooled and collected

(salt is removed)

29

What are the disadvantages of distillation?

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

30

Why is distillation common in the middle east?

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

31

How can you test the purity of water?

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