C3 Hard Water

C3 Hard Water

1. Water that easily forms a rich thick lather with soap is soft water.

2. Hard water is harder to form a lather when mixing soap and water. Instead you get scum which is caused by dissolved calcium ions and magnesium ions. To get a decent lather you need to use more soap.

   • Most hard water is hard because it contains lots of calcium ions and magnesium ions. Rain falling on some types of rock (eg. limestone or chalk) can dissolve compounds like magnesium sulphate and calcium sulphate.
   • Forming hard water: Limestone contains mainly calcium carbonate which is insoluble in water. As rain fall through air, carbon dioxide dissolves in it. Dissolved carbon dioxide makes rainwater acidic. Calcium carbonate reacts with weakly acidic solution so calcium hydrogencarbonate is formed. Calcium ions have entered the water, making it hard.
     • Dissolved ions are carried into reservoirs and onto the domestic water supply.

3. Hard water wastes soap because more soap is needed.

4. How scum/limescale is formed:

   • Insoluble solid can be formed when one type of hard water is heated. E.g. washing machines and this can lead to pipes blocking up.
   • This scale can build up in kettles which makes the heating up of the kettle less efficient. Scale is poor conductor of energy so it takes longer for kettle to boil and uses more energy.

5. There are advantages of drinking hard water which includes that calcium ions are good for healthy teeth and bones. But also studies have shown that it decreases the risk of heart disease.

6. Softening water has benefits including using less water to produce a lather. It is also used in industrial processes because hard water forms scale in boilers.

   • But people are still encouraged to drink hard water for the health benefits.

7. Hard water that can be removed by boiling is temporary hard water. It is temporary hard water because it is caused by hydrogencarbonate atoms.

   • When hard water is boiled the calcium hydrogencarbonate decomposes, then the carbonate ions react with calcium or magnesium ions to form calcium carbonate which is insoluble.
     • Removing hardness through heating would waste energy and therefore it is expensive.

8. Permanent hardness is caused by dissolved calcium sulfate.

   • Can add sodium carbonate. The added carbonate ions reacts with the calcium and magnesium ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate. Calcium and magnesium ions are no longer dissolved in the water so can't make it hard.
   • Can remove calcium and magnesium ions through an ion exchange column. Column usually contains a resin packed with sodium ions and the hard water is passed through it. Sodium ions from resin are exchanged for calcium and magnesium ions. Resin can be recharged with sodium ions by washing it with a salt solution (sodium chloride). This is why water softeners always have to be topped up with salt.