1. Hard and Soft Water

2. Where does our drinking water come from?

3. This means the water we drink has run through and across rocks.

4. This is a map of the rock formations in UK- what does this mean for our water?

5. Depending where you live you will get different chemicals in your tap water..

6. We call the two main water types:
Hard water
Soft water

7. You need to know: The difference between hard and soft water
Which ions cause hard water
How they get there
The pros and cons of each water type
Treatments for water hardness

8. There are 2 metal ions we need to focus on that make water HARD
Calcium – Ca2+
Magnesium – Mg2+

9. REMEMBER
While other metal ions can be in water, only Ca2+ and Mg2+ cause hardness.

10. How do Ca2+ and Mg2+ get into the water?
You need to know the details for calcium
This is a ‘limestone pavement’.
Limestone is calcium carbonate- it does not dissolve in pure water, BUT it does dissolve in acid rain.

11. Acid rain on limestone causes the following reaction:
CaCO3 + H2CO Ca(HCO3)2
Carbonic
Acid (acid rain)
Calcium
Hydrogen
carbonate
Calcium
carbonate

12. So now you have calcium ions (and HCO3- ions) in the water.

13. We say this water is
HARD
Ca2+

14. These are crystals of Calcium sulphate
Look at the tiny tiny man

15. Unlike calcium carbonate (limestone), Calcium sulphate in rocks (Gypsum) is very soluble.

16. Calcium sulphate readily dissolves and puts calcium ions (and sulphate ions) in the water.

17. We say this water is
HARD
Ca2+

18. Calcium Hydrogen carbonate from limestone
Which rocks have put the calcium in your water has important consequences: OR
CaSO4
Ca(HCO3)2
Calcium Sulphate
from gypsum
Calcium Hydrogen carbonate from limestone
Ca2+ ?

19. Both make hard water (ie water with Calcium/ Magnesium ions in it) but….
One is permanent hardness
One is temporary hardness
Ca(HCO3)2
CaSO4
Ca2+

20. Why do we care about water hardness?
3 problems:
Ca2+

21. 1) SCUM

22. Calcium and magnesium ions react with soap to make calcium and magnesium stearate – or scum.
It looks horrible
It’s really hard to get off

23. 2) SOAP
Because the calcium and magnesium ions are reacting with the soap, the soap isn't doing its job ie it isn’t making bubbles.

25. Soft
Hard

26. This matters in hard water areas because everyone ends up using significantly more soap.

27. Both permanent and temporary hardness causes those 2 problems: scum and poor bubbles.

28. This 3rd problem is an issue for areas with temporary hardness, those with limestone rocks and calcium and hydrogen carbonate ions in the water.

29. 3) LIMESCALE

30. Whenever you want to heat up water which has temporary hardness, you get a problem.
The hydrogen carbonate ions (HCO3-)from the limestone are soluble- you wont see them in the water BUT
heat up these ions and they fall apart- making carbonate ions (CO3-)
These then join up with the calcium ions to make calcium carbonate- which is NOT soluble in water (remember it only dissolved in the first place due to acid rain).
This calcium carbonate precipitates out, coating the insides of boilers, kettles, pipes

31. Can you think of any reasons why this,
is a problem?

32. LIMESCALE
It reduces the efficiency of any heating element, using more energy
It can block pipes and damage equipment

33. Are there any positives?
Living in a hard water area clearly causes issues
Some people still prefer it- can you think of any reasons why?

34. Pros of hard water:
Taste- some people prefer it

35. Pros of hard water:
It’s good for your teeth and bones (Calcium ions)

36. Pros of hard water:
Heart- it can protect against heart problems

37. If these positives of living with hard water are not enough to outweigh the negatives, what can you do?

38. Well yes you could move house
What else?

39. Where do the ions in our drinking water come from?
Water runs over rocks and dissolves ions

40. Which 2 ions cause hard water?
Calcium and Magnesium

41. Which rock gives you temporary hard water?
Limestone

42. What is the chemical name for limestone?
Calcium carbonate

43. Why does this normally insoluble chemical dissolve?
Acid rain

44. What ions are produced when limestone reacts with acid rain?
Ca2+ and HCO3-

45. What happens to HCO3- ions if you heat them?
They break down to CO32- ions

46. They precipitate as CaCO3
If you have CO32- ions and Calcium ions in the same water, what happens?
They precipitate as CaCO3

47. What problem arises in heating systems and temporary hard water?
Limescale

48. Why do we care about limescale?
Reduces efficiency/ blocks pipes

49. What rock gives you permanently hard water?
Calcium Sulphate

50. What effect does boiling have on permanently hard water?
None

51. What do calcium and magnesium ions form with soap?
Scum

52. What does this mean for the amount of soap needed?
More soap for the same lather

53. What are the positives to hard water
Taste/ bones and teeth/ heart