Plaster of Paris should be stored in a moisture-proof container because:
A. It reacts with moisture to form a hard solid (gypsum)
B. It sublimes
C. It dissolves in water
D. It evaporates
Answer: Option A
Solution (By JKSSB Mock Tests)
CaSO₄·½H₂O readily absorbs moisture to set to CaSO₄·2H₂O (gypsum), becoming hard and useless for molding. So it must be kept dry. Reaction: CaSO₄·½H₂O + 1½H₂O → CaSO₄·2H₂O.
Explanation:
Temporary hardness is due to Ca(HCO₃)₂ and Mg(HCO₃)₂. Upon boiling, these decompose into insoluble CaCO₃ and Mg(OH)₂, which precipitate out and can be filtered. Thus, boiling effectively removes temporary hardness, and R correctly explains the chemical mechanism involved.
Explanation:
The mass of an atom is almost entirely concentrated in its tiny central nucleus. This is because the nucleus contains protons and neutrons, which are much heavier than the extranuclear electrons. Since electrons have negligible mass, R correctly explains why the mass is localized in the nucleus.
Explanation:
Brass: Cu + Zn. Bronze: Cu + Sn. Stainless steel: Fe + Cr + Ni. Duralumin: Al + Cu + Mg. Brass is used for musical instruments and utensils.
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