Question

The number of moles of ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$ reduce by 1 mol of $S{{n}^{2+}}$ ions is
(A) $\dfrac{1}{3}$
(B) $3$
(C) $\dfrac{1}{6}$
(D) $6$

Answer 1

Hint: Write the balanced equation for the reduction of ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$ tin. From the equation, you can see that the oxidation state of Chromium is changed from +6 to +3, while that of the Tin is changed from +2 to +4.

Complete step by step solution:
-For solving this type of numerical, we begin by writing the balanced ionic equations for the reduction of ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$ by $S{{n}^{+2}}$.
${{K}_{2}}C{{r}_{2}}{{O}_{7}}+14{{H}^{+}}+6{{e}^{-}}\to 2C{{r}^{3+}}+7{{H}_{2}}O$
$(S{{n}^{2+}}\to S{{n}^{4+}}+2{{e}^{-}})\times 3$
-Now, we need to write the balanced net equation of the above reaction.
$3S{{n}^{2+}}+C{{r}_{2}}{{O}_{7}}^{2-}+14{{H}^{+}}\to 3S{{n}^{4+}}+2C{{r}^{3+}}+7{{H}_{2}}O$
-It is clear from the balanced net equation that one mole $C{{r}_{2}}{{O}_{7}}^{2-}$ is reduced by three moles $S{{n}^{2+}}$ .

-Now let us simplify the above equation,
1 mole of $S{{n}^{2+}}$ will reduce = $\dfrac{1}{3}$ moles of $C{{r}_{2}}{{O}_{7}}^{2-}$

Hence the correct answer is option A.$C{{r}_{2}}{{O}_{7}}^{2-}$ .

Additional information:
-Potassium dichromate is an orange-coloured, crystalline, an inorganic compound which is also a strong oxidizing agent.
-Potassium dichromate is a highly corrosive, and irritant chemical.
-Potassium dichromate causes acute toxicity as it emits toxic chromic fumes upon heating. It primarily affects the respiratory tract causing ulcerations, shortness of breath, bronchitis, pneumonia, and asthma.
-Potassium dichromate has carcinogenic properties, i.e it can cause lung cancer and the cancer of the sinonasal cavity.
-Potassium dichromate is denser than water and is soluble in water with no distinctive odour.
-Tin is a silvery-white metal that has a characteristic faint yellow hue. -Tin is a soft metal which can be cut without much force.-Tin resists corrosion from water, but acids and alkalis can attack it.
-Tin is used as a protective coat for other metals. A protective layer of tin oxide (passivation) prevents further oxidation.
-Tin acts as a catalyst in the presence of oxygen.

Note: The oxidation number of a free element is always 0, whereas the oxidation number of a monoatomic ion is equal to the charge of the ion. The sum of oxidation numbers of all the atoms in a polyatomic ion is equal to the charge of the ion.