The addition of gypsum to cement clinker during grinding:
A. Decreases strength
B. Decreases setting time
C. Increases color
D. Increases setting time
Answer: Option D
Solution (By JKSSB Mock Tests)
Gypsum (CaSO₄·2H₂O) is added to clinker to control the rapid reaction of tricalcium aluminate with water, which would otherwise cause flash (quick) setting. Gypsum slows down the hydration of C₃A, thus increasing the setting time and allowing workability. Without gypsum, cement would set almost immediately upon mixing with water, making placement impossible.
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.
Explanation:
Down a group, atomic radius increases and inner shells shield the valence electron, reducing effective nuclear attraction, making electron removal easier.
Explanation:
Aqua regia (royal water) is a 3:1 mixture by volume of concentrated HCl and HNO₃. It generates nascent chlorine and nitrosyl chloride, which oxidize gold and platinum to soluble chloro complexes (e.g., HAuCl₄). Neither acid alone can dissolve these noble metals. Used for cleaning glassware and in etching. Must be prepared fresh and handled with extreme care.
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