Looking for classes? Ksquare Career Institute, Bengaluru →
Which of the statements is not true?
A
$K_2Cr_2O_7$ solution becomes yellow on increasing the pH beyond 7
B
On passing $H_2S$ through acidified $K_2Cr_2O_7$ solution, a milky colour is observed
C
$Na_2Cr_2O_7$ is preferred over $K_2Cr_2O_7$ in volumetric analysis
D
$K_2Cr_2O_7$ solution in acidic medium is orange
Detailed Solution
In alkaline medium orange dichromate changes to yellow chromate: $Cr_2O_7^{2-} + 2OH^- \rightarrow 2CrO_4^{2-} + H_2O$.
Acidified dichromate oxidises $H_2S$ to sulphur, which gives a milky appearance.
$Na_2Cr_2O_7$ is hygroscopic, so it cannot be weighed accurately. $K_2Cr_2O_7$ is not, and is used as a primary standard in volumetric analysis.
So the statement that $Na_2Cr_2O_7$ is preferred is not true.
Acidified dichromate oxidises $H_2S$ to sulphur, which gives a milky appearance.
$Na_2Cr_2O_7$ is hygroscopic, so it cannot be weighed accurately. $K_2Cr_2O_7$ is not, and is used as a primary standard in volumetric analysis.
So the statement that $Na_2Cr_2O_7$ is preferred is not true.