Plaster of Paris hardens on mixing with water due to formation of:
A. CaSO₄
B. CaSO₄·½H₂O
C. CaSO₄·2H₂O
D. CaO
Answer: Option C
Solution (By JKExamLibrary)
Plaster of Paris (CaSO₄·½H₂O) reacts with water to form gypsum (CaSO₄·2H₂O) which sets into a hard solid mass with slight expansion. Reaction: CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O. This property is used for casting and setting broken bones.
Explanation:
Sodium carbonate is a salt of strong base (NaOH) and weak acid (H₂CO₃). On hydrolysis, it gives OH⁻ ions: CO₃²⁻ + H₂O ⇌ HCO₃⁻ + OH⁻, making the solution basic. pH ~11. It turns red litmus blue. It is used for softening hard water and in detergents. NaHCO₃ solution is also mildly basic. Salts of strong acid + strong base are neutral (NaCl). Salts of weak base + strong acid are acidic (NH₄Cl).
Explanation:
Froth flotation separates sulfide ores: powdered ore mixed with water and pine oil; air bubbles carry oil-wetted ore particles to surface as froth; gangue sinks. Used for ZnS, PbS.
Assertion (A): The smell of hot sizzling food reaches you several meters away, but to get the smell from cold food you have to go close. Reason (R): The kinetic energy of gas molecules is higher at higher temperatures.
A.Both A and R are true and R is the correct explanation of A.
B.A is true but R is false.
C.A is false but R is true.
D.Both A and R are true but R is NOT the correct explanation of A.
Explanation:
At higher temperatures, the rate of diffusion increases because the kinetic energy of the gas molecules (food aroma) increases. Thus, the smell of hot food diffuses faster and reaches further. Both statements are correct, and the increased kinetic energy perfectly explains the enhanced diffusion rate observed in the assertion.
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