S - Block Elements MCQ Questions & Answers in Inorganic Chemistry | Chemistry
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251.
By adding gypsum to cement
A
setting time of cement becomes less
B
setting time of cement increases
C
colour of cement becomes light
D
shining surface is obtained
Answer :
setting time of cement increases
The purpose of adding gypsum is only to slow down the process of setting of the cement so that it gets sufficiently hardened.
252.
The molecular formula of a commercial resin used for exchanging ions in water softening is $${C_8}{H_7}SO_3^ - N{a^ + }$$ $$\left( {Mol.\,wt.\,206} \right).$$ What would be the maximum uptake of $$C{a^{2 + }}$$ ions by the resin when expressed in mole per gram resin?
A
$$\frac{2}{{309}}$$
B
$$\frac{1}{{412}}$$
C
$$\frac{1}{{103}}$$
D
$$\frac{1}{{206}}$$
Answer :
$$\frac{1}{{412}}$$
$$2$$ mole of water softner require $$1$$ mole of $$C{a^{2 + }}$$ ion $$1$$
So, $$1$$ mole of water softner require $$\frac{1}{2}$$ mole of $$C{a^{2 + }}$$ ion
Thus, $$\frac{1}{{2 \times 206}} = \frac{1}{{412}}{\text{moI/g}}$$ will be maximum uptake
253.
The correct order of increasing thermal stability of $${K_2}C{O_3},MgC{O_3},CaC{O_3}$$ and $$BeC{O_3}$$ is
A
$$BeC{O_3} < MgC{O_3} < {K_2}C{O_3} < CaC{O_3}$$
B
$$BeC{O_3} < MgC{O_3} < CaC{O_3} < {K_2}C{O_3}$$
C
$$MgC{O_3} < BeC{O_3} < CaC{O_3} < {K_2}C{O_3}$$
D
$${K_2}C{O_3} < MgC{O_3} < CaC{O_3} < BeC{O_3}$$
Thermal stability of carbonates increases in a group as we move from top to bottom and decreases in a period as we move from left to right, so the correct order of thermal stability of given carbonates is $$BeC{O_3} < MgC{O_3} < CaC{O_3} < {K_2}C{O_3}$$
$$Be, Mg$$ and $$Ca$$ are present in second group and $$K$$ is present in first group.