Chemistry 3 Unit 2

Soft water is water that lathers easily with soap

• Hard water needs more soap to produce lather to wash effectively.
• This is because hard water contains dissolved compounds to react with the soap to produce scum

This is an insoluble solid which is the precipitate formed when soap reacts with calcium or magnesium ions in hard water

Because there is no soap to react with the Calcium or magnesium ions in hard water

Temporary hard water softens when boiled, permanent hard water stays hard

Hydrogen-carbonate ions

• Temporary hard water contains hydrogen-carbonate ions that decompose when heated to produce carbonate ions, water and carbon dioxide
• 2HCO3 ~> CO3 + H2O + CO2

Carbonate ions react with calcium and magnesium ions to produce precipitates of calcium carbonate and magnesium carbonate, that are deposited as scale

Hard water can increase costs because more soap is needed to wash effectively

When temporary hard water is heated it can produce scale which can reduce the efficiency of the heating system and cause blockages

• Hard water contains calcium compounds which are good for our health
• Helps the development of strong bones and teeth
• Can help reduce the risk of heart disease

Hard water can be softened by removing the calcium and magnesium ions which react with soap

• Add sodium carbonate. This reacts with the calcium and magnesium ions to form solid precipitates of calcium carbonate and magnesium carbonate which cannot react with soap
• Use ion-exchange columns containing sodium and hydrogen ions(resin). This resin carries the calcium and magnesium ions and sodium and hydrogen ions replace them as they pass through the column

High levels of dissolved salts and microbes

• Choosing an appropriate water source
• Sedimentation or filtration of the water removes any solids
• The water is then sterilised with chlorine to kill microbes

Water filters contain carbon, silver and ion-exchange resins that remove dissolved substance from the water to improve the taste

Distillation

Distillation requires a large amount if energy to boil the water; therefore it would be very expensive to do on a large scale