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?
$$2$$ 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.