Question

One mole of acidified $\,{K_2}C{r_2}{O_7}\,$ ​ on reaction with excess of $KI$ will liberate moles of ${I_2}$
A.$3$
B.$1$
C.$7$
D.$2$

Answer 1

Potassium dichromate is a very strong oxidizing agent. It reacts with iodide within the presence of acid to supply Chromium sulphate, Potassium sulphate, iodine, and water. Potassium dichromate is employed as an oxidising agent in chemistry, and is milder than the permanganate of potash. It will be wont to oxidize alcohols. It converts primary alcohols into aldehydes and, under more forcing conditions, into carboxylic acids.

Complete step by step answer:
When one mole of acidified potassium dichromate ($\,{K_2}C{r_2}{O_7}\,$) reacts with excess of $KI$ solution, the balanced chemical reaction will be as follows:
$\,C{r_2}{O_7}^{2 - } + 14{H^ + } + 6{I^ - } \to 2C{r^{3 + }} + 3{I_2} + 7{H_2}O\;\,$
From the reaction, we observe the following:
This is a redox reaction as-
Chromium will get reduced from $+ 6 \to + 3$ oxidation state
Iodine will be oxidized from $- 1 \to 0$ oxidation state.
A redox reaction is defined as a chemical reaction in which electrons are transferred between two reactants participating in it. This transfer of electrons will be identified by observing the changes in the oxidation states of the reacting species. Electron-accepting species are the ones that tend to undergo a reduction in redox reactions and are called oxidizing agents. An electron-donating species which tends to hand over electrons can be called as a reducing agent. These species usually tend to undergo oxidation.
$3$moles of ${I_2}$​ is evolved, when excess of $KI$ react with one mole of acidified potassium dichromate $\,{K_2}C{r_2}{O_7}\,$
So the correct answer is A.

Note: Permanganate tends to relinquish carboxylic acids . Within the presence of dichromate, Secondary alcohols are usually converted into ketones. For example, methanone is also prepared by oxidation of menthol with acidified dichromate. Tertiary alcohols can’t be oxidized.
-In a solution the colour change observed are often wont to test for distinguishing aldehydes from ketones. Aldehydes often reduce dichromate from the $+ 6 \to + 3$ oxidation number, changing colour from orange to green. This colour change arises because the aldehyde is also oxidized to the corresponding acid.