1. Hard water

2. LI – to know the causes, effects and cures for hard water
Hard water is hard to lather and forms a scum with soap
It is caused by the presence of dissolved calcium or magnesium compounds
Detergents are not affected by hard water
There are 2 types of hardness; temporary and permanent
Hardness is tested for using soap solution
The greater volume of soap needed the harder the water

3. Temporary hardness
Temporary hard water is formed by rain water reacting with the limestone.
Rain water is slightly acidic due to the presence of dissolved carbon dioxide
Rain water is a weak solution of Carbonic acid, H2CO3
Calcium + Water + Carbon = Calcium
carbonate dioxide hydrogen carbonate
CaCO3(s) + H2O (l) + CO2(g) = Ca(HCO3)2(aq)

4. Features of hard water areas
Stalactites and stalagmites are found in limestone regions. These are formed by the decomposition of the calcium hydrogen carbonate inside the limestone caves

5. Temporary hardness Temporary hardness can be removed by boiling
Calcium hydrogen carbonate decomposes on heating
Ca(HCO3)2 = CaCO3 + H2O + CO2
Limescale is formed when temporary hard water decomposes

6. Permanent Hardness
Permanent hard water is caused by Calcium or magnesium sulphate
Calcium sulphate and magnesium sulphate is slightly soluble and dissolve when rain water runs over the rocks like granite
Permanent hard water is not softened by boiling

7. Q: Explain why water in limestone regions is hard when limestone is insoluble.
Rain water contains dissolved carbon dioxide which makes it acidic (carbonic acid). The acidic rain water reacts with the calcium carbonate (limestone) and forms soluble calcium hydrogen carbonate.
CaCO3(s) + H2O(l) + CO2(g) = Ca(HCO3)2(aq)

8. Hard water can be good and can be a nuisance
Good points
Tastes better
Contains calcium which is good for teeth & bones
Good for tanning leather
Bad points
Wastes soap
Leaves a fur inside kettles so harder to boil
Leaves limescale inside pipes

9. Curing Hardness Boiling – removes temporary hardness only
Adding washing soda (sodium carbonate) –removes both types of hardness
Ion exchange –changes the calcium ions for sodium ions

10. Equations for curing hardness - Higher
Boiling:
Ca(HCO3)2 = CaCO3 + H2O + CO2
Washing soda (sodium carbonate)
Na2CO3 + CaSO4 = Na2SO4 + CaCO3
Ion Exchange
Ca 2+ swapped for 2Na+

11. Exam questions - Higher
Q: Explain in terms of ions how washing soda softens water
A: The calcium ions from the hard water reacts with the carbonate ions from the washing soda to form insoluble calcium carbonate

12. Exam questions - Higher
Q: Explain in terms of ions how an ion exchanger softens water
A: The calcium ions from the hard water are swapped for sodium ions from the exchanger
The water no longer contains calcium ions and therefore is no longer hard