The addition of gypsum to cement clinker is done to:
A. Change the color of cement.
B. Increase the strength of cement.
C. Make it waterproof.
D. Slow down the initial setting time.
Answer: Option D
Solution (By JKSSB Mock Tests)
Gypsum (CaSO₄·2H₂O) is added to cement clinker (about 3-5%) to retard the setting time. Without gypsum, cement would set almost immediately upon adding water (flash set) due to the rapid reaction of tricalcium aluminate. Gypsum allows sufficient time for mixing and placing.
Explanation:
Finely divided nickel catalyzes the addition of hydrogen to liquid oils to form solid fats (vanaspati ghee). Platinum/palladium also work but are expensive. Iron is used in Haber process; V₂O₅ in Contact process.
Explanation:
Petroleum is a mixture of hydrocarbons with close boiling points. Fractional distillation uses a fractionating column to separate them efficiently based on repeated condensation–vaporization cycles. Simple distillation cannot separate liquids with boiling point difference less than 25 K effectively. Filtration and sublimation are not applicable.
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