Question

The equivalent weight of ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$ in acidic medium is expressed in terms of its molecular weight (M) as –
(A) M/3
(B) M/4
(C) M/6
(D) M/7

Answer 1

Hint: Equivalent weight is related to molecular weight by the equation –
Equivalent weight = molecular weight / chemical equivalent.
We will get the answer in terms of molecular weight by substituting the chemical equivalent.

Complete step by step solution:
- Let us first understand the concepts of molecular weight and equivalent weight.
- Molecular weight is the mass of one molecule of a particular compound. The molecular weight of a particular molecule can be found using its chemical formula. The sum of atomic weights of the atoms in the molecule gives you the molecular weight.
- The equivalent weight can be defined as the ratio of molecular weight to the chemical equivalent. The chemical equivalent can be calculated by finding the number of electrons that participate in the chemical reaction.
- Molecular weight is related to equivalent weight by the formula –
Equivalent weight = molecular weight / chemical equivalent
- This equation can be used to find the equivalent weight from the molecular weight of the substance.
- We have to find the equivalent weight of ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$ in acidic medium. ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$ in acidic medium gives the following ions-
${{K}_{2}}C{{r}_{2}}{{O}_{7}}+14{{H}^{+}}+6{{e}^{-}}\to 2{{K}^{+}}+2C{{r}^{3+}}+7{{H}_{2}}O$
- Hence, we can conclude that the chemical equivalent is 6. This is because there are 6 electrons participating in the chemical reaction.
- We have to find the equivalent weight in terms of molecular weight. So let us take the molecular weight of ${{K}_{2}}C{{r}_{2}}{{O}_{7}}$ to be M.
- Let us now substitute the molecular weight and chemical equivalent in the equation.
Equivalent weight = M / 6.
- Hence, the answer is option (C) M/6.

Note: Molecular weight should not be confused with molar mass. Molar mass and molecular weight are two different concepts. Molar mass is the mass of one mole of a given compound. Whereas, molecular weight is the mass of one molecule of a particular compound.