Question

$2.47g$ of $CuO$ were obtained by oxidizing $1.986g$ of copper by a mineral acid. $0.335g$ of copper was precipitated by $0.346g$ of zinc from $CuS{{O}_{4}}$ solution. Determine the equivalent weights of copper and zinc.

Answer 1

Hint: We can get the equivalent weights of copper and zinc by applying the direct formula for the equivalent weight. Remember, the equivalent weight of an element is directly proportional to its mass given. By applying this relationship also we can find out the equivalent weights of the given element.

Complete step by step solution:
Given that,
$2.47g$ of $CuO$ were obtained by oxidizing $1.986g$ of copper by a mineral acid. And, then $0.335g$ of copper was precipitated by $0.346g$ of zinc from $CuS{{O}_{4}}$ solution.
So, here we can say that:
The mass of the metal oxide i.e. $CuO$ is given as $2.47g$.
The mass of the metal present in that metal oxide is given as $1.986g$.
And the mass of the oxygen present in that oxide is not given. We know that the mass of the metal oxide will be the total sum of the mass of copper and oxygen that is present in the oxide.
So, the mass of the oxygen present in the metal oxide will be different between the mass of the metal oxide and the mass of the metal. Thus, the mass of oxygen will be $(2.47-1.986) g=0.484g$.
The equivalent weight of a metal in an oxide equals the ratio of the mass of the metal to that of mass of the oxygen present in that oxide multiplied with the mass which combines with the $8g$ of oxygen.
So, equivalent weight of copper in copper oxide will be
$=\dfrac{\text{Mass of the metal}}{\text{Mass of oxygen present in the oxide}}\times 8$
Then it will be, $\dfrac{1.986}{0.484}\times 8=32.82g$
Again, in the question it is given as,
Mass of the copper and zinc in $CuS{{O}_{4}}$ are $0.335g$ and $0.346g$respectively.
We can say that, equivalent weight is directly proportional to the mass of an element.
So, $\dfrac{\text{Equivalent weight of copper}}{\text{Equivalent weight of zinc}}=\dfrac{\text{Mass of copper}}{\text{Mass of zinc}}$
Thus, Equivalent weight of zinc will be $=\dfrac{32.82\times 0.346}{0.335}=33.89g$

Hence, the equivalent weight of copper is $32.82g$ and that of zinc is $33.89g$.

Note: It is important to note that, the equivalent mass or weight is the mass of one equivalent. So, we can conclude that the equivalent weight of an element is the mass which will combine with or displace $1.008g$ of hydrogen or $8g$ of oxygen and so on. It is directly proportional to the mass of an element.