1. Ch-10 Hard and Soft Water
Science 7th grade

3. Introduction .
What is Water Hardness?
Video:

4. Topic .
Groundwater dissolves rocks and minerals releasing calcium, magnesium, and other ions that cause water to be hard. These dissolved ions give hard water its characteristics.

5. Hard Water What do you think the term “hard water” means?
Note: Water where you live might be hard or soft – this depends on the rocks the water meets on its way to you…

6. Hard Water
Hardness refers to the presence of calcium and magnesium ions in water (and sometimes iron).
Ions come from dissolved rock the water has passed through.
Affects properties of tap water

7. Hard Water Minerals in hard water interact with soap.
Interferes with soap’s ability to lather.

8. Hardness levels vary in different geographic regions.
Topic .
Hardness levels vary in different geographic regions.

9. Topic .
So, what’s the big deal?
Why is hardness bad?

10. Module Objectives
It costs you
MONEY !!

11. Calcium and iron deposits can build up in appliances and on faucets:
Washing machine
Dish washer
Steam iron
Shortens their life span and adds to landfill problem!
Hard Water causes damage to the hair.

12. Hardness minerals precipitate out of the water and form energy robbing scale.

13. Wastage of Energy

15. Positive effects of Hard water
Most people agree that it tastes better.
It is thought to reduce the number of heart illnesses.
It provides useful calcium ions for the healthy growth of bones and teeth.
The formation of lime scale in pipes (see below) causes the inside of the pipe to be covered with insoluble bicarbonates. This layer prevents the hot water from coming in contact with the surface of the pipe.
This prevents corrosion of metal and also from dissolving of harmful metals in water.

16. Lab activity: Testing for Hard Water
Three samples of water
Hard water
Tap water (?)
Distilled water
Your job is to find out which sample is which!

17. 1 beaker
3 test tubes
Marker
Eyedropper
Label test tubes with marker and tape:
A B C

18. Place 10ml of water in each corresponding test tube
Observe your 3 samples
Can you tell by observing and touching which one is hardest?
Water hardness affects a soap’s ability to lather: the harder the water the fewer soap suds will form.
How can this fact help you determine which sample is the hardest?

19. Lab activity: Testing for Hard Water
Three samples of water
Hard water
Tap water (?)
Distilled water
Your job is to find out which sample is which!

20. Soft Water Water with very low concentrations of minerals.
Soap lathers easily and is sometimes difficult to rinse off.

21. Distilled Water
Water that has been purified through evaporation and condensation so remove minerals such as calcium.
Is distilled water soft water?

23. Types of Hard Water Water is hard both temporarily and permanently…
Temporary hardness if caused by hydrogencarbonate ions (HCO3-) in Ca(HCO3)2
Permanent hardness is caused by, amongst other things, dissolved calcium sulfate

24. Ca(HCO3)2(aq)  CaCO3(s) + H2O(l) + CO2(g)
Temporary Hardness
Temporary hardness is removed by boiling – the Ca(HCO3)2 decomposes forming calcium carbonate which is insoluble (“limescale”)
Ca(HCO3)2(aq)  CaCO3(s) + H2O(l) + CO2(g)

25. Temporary & Permanent Hardness
Temporary and permanent hardness can be softened by adding washing soda (Na2CO3)
The carbonate ions react with the calcium ions and magnesium ions making an insoluble precipitate of calcium carbonate and magnesium carbonate
As the calcium ions and magnesium ions are no longer dissolved in the water they cannot make it hard
Ca+2(aq) + CO3-2(aq)  CaCO3(s)

26. Temporary & Permanent Hardness
Temporary and permanent hardness can be softened by running the water through an ion exchange column which contain sodium ions or hydrogen ions which exchange them for calcium ions and magnesium ions
Na2Resin(s) + Ca+2(aq)  CaResin(s) + 2Na+(aq)
*Resin is a large insoluble resin molecule

27. How Water Softeners Work
Hard water, loaded with Calcium, Magnesium, and many other ions, enters the water softener and contacts millions of special resin beads which hold billions of sodium ions. The Calcium, Magnesium, and other ions trade places with the Sodium ions, creating softened water.

28. How Water Softeners Work SOFTENING CYCLE
Capacity to soften water now ending
Water Softener
Hard water enters
Many gallons later
Regeneration with salt brine now required
Sodium charged ion exchange resin
Softened water containing sodium ions
Partially exhausted, but still delivering 100% soft water

29. How Water Softeners Work REGENERATION CYCLE
Waste water containing hardness in exchange for sodium
Softener still discharging waste water
Excess salt brine also removed
Regeneration complete
Ready for ion exchange softening
Salt brine, most economical source of sodium
15 to 20 minutes later
Regeneration almost completed

30. Typical Water Softener

31. Water Softeners Remove Other Contaminants
Nearly any positively charged cation can be captured by a typical water softener using standard cation exchange resin, i.e. Iron, Manganese, Lead, Aluminum, Barium, Cadmium, Copper, Potassium, Radium, Silver, Strontium, Uranium (depending on valence).
This is not a comprehensive list, and specific water chemistry may affect removal rates.

33. Ever heard of Heavy Water ??

34. Heavy Water
Heavy water is water that contains heavy hydrogen or deuterium.
Deuterium differs from the hydrogen usually found in water, Protium, in that each atom of deuterium contains a proton and a neutron.
Heavy water may be deuterium oxide, D2O or it may be deuterium protium oxide, DHO.
Heavy water occurs naturally, although it is much less common than regular water.
Approximately one water molecule per twenty million water molecules are heavy water.

43. Conclusion Why is distilled water the softest?
Which water sample is most likely to contribute to water pollution? Explain