Question

Equivalent weight of ${{{K}}_2}{{Cr}}{{{O}}_4}$, when it reacts with ${{AgN}}{{{O}}_3}$ to give ${{A}}{{{g}}_2}{{Cr}}{{{O}}_4}$ is:
A. infinite
B. ${{M}}$
C. $\dfrac{{{M}}}{2}$
D. $\dfrac{{{M}}}{3}$

Answer 1

Hint: Equivalent weight is calculated by dividing molecular weight by its valency. Valency depends on the total charge of the ions. It may be different in the acid-base concept. Equivalent weight is the weight of a molecule which has one equivalent of proton in acids and hydroxide in bases.

Complete step by step answer:
Before calculating the equivalent weight of ${{{K}}_2}{{Cr}}{{{O}}_4}$, let’s know about the molecular weight and equivalent weight.
Molecular weight is calculated using chemical formula. The chemical formula of potassium chromate is ${{{K}}_2}{{Cr}}{{{O}}_4}$. It is the sum of atomic weights of each element in a compound.
Now let’s calculate the molecular weight of potassium chromate. Atomic weight of potassium is $39$, chromium is $52$ and oxygen is $16$. There are two potassium atoms and four oxygen atoms. Thus we have to multiply the atomic weight of potassium with two and that of oxygen with four.
It can be calculated as $\left( {39 \times 2} \right) + 52 + \left( {16 \times 4} \right) = 194$
Molecular weight is represented by ${{M}}$.
Equivalent weight is the ratio of molecular weight to the valency where valency is the total charge of cation. Thus valency is $2$.
Thus equivalent weight is $\dfrac{{{M}}}{2}$.

Hence, the correct option is C.

Additional information:
Equivalent weight differs with the type of reaction. The equivalent weight of a substance divided by its volume in litre of solution is known as the normality of a solution.

Note: In acid-base concept, equivalent weight will be calculated using protons or hydroxide. Equivalent weight is also known as gram equivalent. The reaction which occurs when potassium chromate is reacted with silver nitrate is given below. It produces two moles of potassium nitrate and silver chromate.