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) 16
b) 32
c) 48
d) 64

Answer 1

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.

Complete answer:
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.