Plaster of Paris is obtained by heating gypsum at:
A. 473 K
B. 573 K
C. 373 K
D. 673 K
Answer: Option C
Solution (By JKSSB Mock Tests)
Plaster of Paris (CaSO₄·½H₂O) is formed by heating gypsum (CaSO₄·2H₂O) at 373 K (100°C). This causes it to lose 1.5 molecules of water per formula unit. If heated significantly above 473 K, it loses all water and forms dead burnt plaster (anhydrous CaSO₄), which cannot set with water.
Explanation:
Ozone (O₃) has a coordinate bond (dative bond). One oxygen atom donates a lone pair to another oxygen atom. The Lewis structure shows O=O⁺–O⁻ or resonance. NaCl is ionic; H₂O has polar covalent bonds; NH₃ has ordinary covalent bonds (though it can donate a lone pair to form coordinate bond in NH₄⁺).
Explanation:
CNG (methane) has a higher H/C ratio, so combustion produces less CO₂ per unit energy compared to petrol/diesel. It also burns completely without generating smoke or particulate matter, and contains no sulfur, thus no SO₂. It reduces NOx and unburned hydrocarbons. It is used in vehicles and is safer in spills because it is lighter than air and disperses quickly.
Explanation:
Permanent hardness (due to CaSO₄ etc.) can be removed by adding Na₂CO₃, which precipitates CaCO₃. Boiling only removes temporary hardness. Ion exchange and calgon also work.
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