Question

${\text{4}}\,{\text{g}}$ of copper was dissolved in concentrated nitric acid. The copper nitrate solution on strong heating gave ${\text{5}}\,{\text{g}}$ of its oxide. The equivalent weight of copper is:
(A) 23
(B) 32
(C) 12
(D) 20

Answer 1

The weight of the substance given either molecular weight also called molar mass or equivalent weight.The molecular weight is the average mass or weight of the molecule given. The unit of molecular weight is gram per mole.The equivalent weight of the substance is the mass of the substance that combines with eight grams of oxygen or one gram of the hydrogen atom.The unit of the equivalent weight is gram per equivalent.

Complete step-by-step solution: The chemical formula of the copper oxide is ${\text{CuO}}$.
Here, it is given that ${\text{4}}\,{\text{g}}$ of copper on reaction with nitric acid first gives copper nitrate solution. This copper nitrate solution on heating gives off ${\text{5}}\,{\text{g}}$ copper oxide.
As ${\text{4}}\,{\text{g}}$ of copper converted into ${\text{5}}\,{\text{g}}$ copper oxide indicates there is $1\,{\text{g}}$ of oxygen is there.
As equivalent weight is nothing but the weight of substance combines with eight grams of the oxygen, determine the equivalent weight of the copper as follows:
Here, consider x as the equivalent weight of the copper.
${\text{4}}\,{\text{g}}\,{\text{of}}\,{\text{copper}}\,{\text{ = }}\,1\,{\text{g}}\,{\text{of}}\,{\text{oxygen}}$
$\,8\,{\text{g}}\,{\text{of}}\,{\text{oxygen}}\,{\text{ = }}\,{\text{x}}\,{\text{g}}\,{\text{of}}\,{\text{copper}}\,$
${\text{x}}\,{\text{g}}\,{\text{of}}\,{\text{copper}}\, = \dfrac{{8\,{\text{g}}\,{\text{of}}\,{\text{oxygen}} \times {\text{4}}\,{\text{g}}\,{\text{of}}\,{\text{copper}}}}{{\,\,1\,{\text{g}}\,{\text{of}}\,{\text{oxygen}}}}$
${\text{x}}\,{\text{g}}\,{\text{of}}\,{\text{copper}}\, = 32\,{\text{g}}\,{\text{of}}\,{\text{copper}}$
Thus, the equivalent weight of the copper is $32\,{\text{g per equivalent}}$.

Option(B) 32 is the correct answer to the given question.

Note: The equivalent weight of the substance is also calculated using the formula as follows:
${\text{equivalent weight = }}\dfrac{{{\text{molecular}}\,{\text{weight}}}}{{{\text{acidity}}\,{\text{or}}\,{\text{basicity}}\,{\text{of}}\,{\text{substance}}}}$
Here, the term acidity is used in the case of the basic substances, and acidity is used in the case of the acidic substances.Here, the chemical formula of the copper oxide is ${\text{CuO}}$and copper nitrate is ${\text{Cu}}{\left( {{\text{N}}{{\text{O}}_3}} \right)_2}$.