Question

# 2.8 g of iron displaced 3.2 g of copper from a solution of copper sulphate. If the equivalent mass of iron is 28, the equivalent mass of copper will be:a) 16b) 32c) 48d) 64

Hint:For finding the equivalent weight we should know the molar masses and amount of one metal displaced by another. Equivalent weight is also known as gram equivalent.

We know that equivalent weight is the mass of one equivalent, that is the mass of a given substance which will combine with or displace a fixed quantity of another substance.
And in the question it is given that 2.8g of iron (Fe) displaces 3.2g of copper (Cu) from a solution of copper sulphate ($CuS{{O}_{4}}$).
Then for finding the equivalent mass of copper:
Let,
W = mass displaced, E = equivalent mass.
Then we know that equivalent amount displaced and occupied will be equal:

$\dfrac{{{W}_{Cu}}}{{{E}_{Cu}}}=\dfrac{{{W}_{Fe}}}{{{E}_{Fe}}}$
By putting all the given data in above equation:

$\dfrac{3.2}{{{E}_{Cu}}}=\dfrac{2.8}{28}$
By solving the above equation:
$\dfrac{3.2}{{{E}_{Cu}}}$= 0.1,
Then,
${{E}_{Cu}}$(Equivalent mass of the copper (Cu) = (3.2 / 0.1)
${{E}_{Cu}}$= 32 g/eq.
So, the equivalent weight of copper (Cu) is 32.

Then the correct answer is option “B”.

Note: We can say that equivalent weight is more complicated. The equivalent weight doesn’t have any unique value for a given compound. Example:$KMn{{O}_{4}}$ has more than one value of equivalent weight. A reaction in which the species is involved must be specified in order to get a value of equivalent weight for a species.