In the reaction of potassium dichromate, potassium chloride and sulfuric acid (conc.), the oxidation state of the chromium in the product is (+)_______.

Question

Statement-I : Consider the following pairs of ions $(\text{Sc}^{3+}, \text{Ti}^{3+}), (\text{Ti}^{4+}, \text{Ni}^{2+}), (\text{Cu}^{2+}, \text{Zn}^{2+})$ and $(\text{Cr}^{3+}, \text{Mn}^{3+})$. Out of these pairs three pairs consist of ions that are both coloured :
Statement-II : Among the lanthanide ions $\text{Eu}^{2+}$, $\text{Gd}^{3+}$, $\text{Ce}^{4+}$ and $\text{Tb}^{4+}$, the ion $\text{Tb}^{4+}$ is the strongest reducing agent.
Choose the correct option.

Answer 1

The reaction of potassium dichromate, potassium chloride, and concentrated sulfuric acid produces chromyl chloride ($CrO_2Cl_2$). The balanced equation is:

$K_2Cr_2O_7 + 4KCl + 6H_2SO_4 \rightarrow 2CrO_2Cl_2 + 6H_2O + 3K_2SO_4$

In $K_2Cr_2O_7$, chromium has an oxidation state of $+6$. This oxidation state is maintained in chromyl chloride ($CrO_2Cl_2$). To verify, let the oxidation state of $Cr$ in $CrO_2Cl_2$ be $x$, with oxygen at $-2$ and chlorine at $-1$:

\[x + 2(-2) + 2(-1) = 0\]
\[x - 4 - 2 = 0\]
\[x = +6\]
This calculation confirms that chromium's oxidation state is $+6$ in $CrO_2Cl_2$, consistent with the given range (6,6). The oxidation state of chromium in the product is therefore $+6$.

In the reaction of potassium dichromate, potassium chloride and sulfuric acid (conc.), the oxidation state of the chromium in the product is (+)_______.

Correct Answer: 6

Solution and Explanation

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