Question

Assertion :Potassium chromate solution in acetic acid precipitates only $B{a}^{2+}$ as $BaCr{O}_4$ in group V. Reason: $SrCr{O}_4$ and $CaCr{O}_4$ are not precipitated with potassium chromate solution in acetic acid.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is incorrect but Reason is correct
• D. Both Assertion and Reason are correct

Answer 1

The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

Potassium chromate solution gives a yellow precipitate of barium chromate when the solution containing $B{a}^{2+}$ in acetic acid is treated with it.
$B{a}^{2+}+C{H}_{3}COOH\to (C{H}_{3}COO{)}_{2}Ba+H^{+}+C{O}_2$
$(C{H}_{3}COO{)}_{2}Ba+K_{2}Cr{O}_4\to BaCr{O}_4\downarrow (\text{yellow ppt})+C{H}_{3}COOK$
$SrCr{O}_4$ and $CaCr{O}_4$ are not precipitated with potassium chromate solution in acetic acid because $K_{sp}$ value of $SrCr{O}_4$ and $CaCr{O}_4$ are much higher than $BaCr{O}_4$. Addition of acetic acid lowers the concentration of $Cr{O}_4^{2-}$. Hence $BaCr{O}_4$ is precipitated only because of its low $K_{sp}$ value.