Question

Let the mass of a metal (hypothetical) in its oxide is $75\%$ of the mass of the whole compound. Calculate its equivalent mass.

• A. $8gm$
• B. $16gm$
• C. $24gm$
• D. $32gm$

Answer 1

The correct option is C $24gm$

Taking the basis as 100 g of the compound, it has 75 g metal and 25 g oxygen in it.
$m_M=75g,m_O=25g$
The number of equivalents of both the metal and oxygen must be the same in the compound.
$(n_E{)}_{metal}=(n_E{)}_{oxide}$
$n_E=\frac{Givenmass}{Equivalentmass}=\frac{m_M}{E_M}$
$E_M=\frac{m_M}{(n_E{)}_{oxide}}$
The oxide ion which has a molar mass of 16 g/mol has a negative two charge, so its equivalent mass:
$E_O=\frac{16}{2}=8g$
$E_M=75\times \frac{8}{25}=24g$