Hard & soft water

The video explains the concept of water hardness, distinguishing between soft and hard water. Hardness is caused by calcium ions from soluble salts in rocks. Rainwater is soft because it lacks these salts. Temporary hardness, caused by calcium carbonate, can be removed by boiling, while permanent hardness, from calcium sulfate, cannot. Soap forms scum in hard water due to calcium ions, but detergents do not have this issue. The video concludes with a summary of these concepts.

What is the primary cause of water hardness?

• Presence of sodium ions

• Presence of calcium ions

• Presence of magnesium ions

• Presence of potassium ions

Why is rainwater considered soft?

• It contains calcium ions

• It flows through rocks

• It contains dissolved salts

• It evaporates from the sea leaving salts behind

What happens when rainwater reacts with limestone?

• It forms calcium sulfate

• It forms calcium hydrogen carbonate

• It forms calcium chloride

• It forms calcium nitrate

How can temporary hardness be removed?

• By freezing the water

• By adding more calcium

• By boiling the water

• By adding soap

Why do detergents not form scum in hard water?

• They are made from natural fats

• Their calcium salts are soluble

• They contain calcium ions

• They do not react with water