Q1Engineering Chemistry

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PART - A

Q.1 Define the term hardness of water.

Answer 1

Hardness in water fundamentally prevents the easy formation of lather with standard soap solutions. Chemically, standard soap is fundamentally the water-soluble sodium or potassium salt of long-chain high-molecular-weight fatty acids (like sodium stearate, $C_{17} H_{35} C O O N a$ ).

When soap is systematically added to "hard" water, the highly reactive dissolved $C a^{2 +}$ and $M g^{2 +}$ ions instantaneously violently react directly with the soluble soap molecules. This aggressive chemical displacement strictly forms a highly insoluble, totally inactive, sticky white precipitate universally known as 'scum' (calcium or magnesium stearate).

2 C_{17} H_{35} C O O N a (S o a p) + C a^{2 +} \to (C_{17} H_{35} C O O)_{2} C a ↓ (I n so l u b l e S c u m) + 2 N a^{+}

Q1Engineering Chemistry

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