Question

Washing soaps produce scum with hard water and not much foam because hard water contains:

• A. chalk and sulphur
• B. many dissolved inorganic salts
• C. many suspended particles
• D. organic matter

Answer 1

The correct option is B many dissolved inorganic salts

Hard water contains salts of calcium and magnesium principally as bicarbonates, chlorides, and sulfates. Ferrous ion may also be present, oxidized to the ferric form. It appears as a reddish-brown stain on washed fabrics and enameled surfaces. Water hardness that is caused by calcium bicarbonates is known as temporary because boiling converts the bicarbonates to the insoluble carbonates, hardness from other salts is called permanent. Calcium and magnesium ions in hard water react with the higher fatty acids of soap to form an insoluble gelatinous curd, thereby causing a waste of the soap.