JEE PYQ: S Block Elements Question 7
Question 7 - 2021 (18 Mar Shift 1)
Given below are two statements:
Assertion A: During the boiling of water having temporary hardness, $\text{Mg(HCO}_3)_2$ is converted to $\text{MgCO}_3$.
Reason R: The solubility product of $\text{Mg(OH)}_2$ is greater than that of $\text{MgCO}_3$.
In the light of the above statements, choose the most appropriate answer from the options given below:
(a) Both A and R are true but R is not the correct explanation of A (b) A is true but R is false (c) Both A and R are true and R is the correct explanation of A (d) A is false and R is also false
Show Answer
Answer: (d)
Solution
For temporary hardness, $\text{Mg(HCO}_3)_2 \xrightarrow{\text{heating}} \text{Mg(OH)}_2 \downarrow + 2\text{CO}_2 \uparrow$. Assertion is false because $\text{Mg(HCO}_3)_2$ converts to $\text{Mg(OH)}_2$, not $\text{MgCO}3$. $K{sp}$ of $\text{MgCO}3 = 3.5 \times 10^{-8}$ and $K{sp}$ of $\text{Mg(OH)}2 = 1.8 \times 10^{-11}$. So $K{sp}$ of $\text{MgCO}_3$ is greater than $\text{Mg(OH)}_2$, hence R is also false.
BETA
