# Question #5dec3

May 17, 2017

The equivalent mass of ${\text{K"_2"Cr"_2"O}}_{7}$ is 49.03 g.

#### Explanation:

The equivalent mass of a substance is the mass that will supply or react with one mole of electrons in a redox reaction.

The half-reaction for the dichromate ion is

$\text{Cr"_2"O"_7^"2-" + "14H"^"+" + "6e"^"-" → "2Cr"^"3+" + 7"H"_2"O}$

1 mol of $\text{Cr"_2"O"_7^"2-}$ reacts with 6 mol of electrons, so

1 mol of ${\text{K"_2"Cr"_2"O}}_{7}$ reacts with 6 mol of electrons

$\text{Equivalent mass of K"_2"Cr"_2"O"_7 = "molar mass"/6 = "294.18 g"/6 = "49.03 g}$