Question

The specific heat of metal is $0.67$ J/g. Its equivalent mass is $20$. Its exact atomic mass is :

• A. $46$
• B. $20$
• C. $40$
• D. $22$

Answer 1

The correct option is C $40$

Dulong Petit's law states that the gram-atomic heat capacity (specific heat x atomic weight) of an element is a constant. It is the same for all solid elements, about six calories per gram atom.
Specific heat $\times$ Atomic mass $=6.4$
According to the given conditions,
$\frac{0.67}{4.18}\times$ Atomic mass $=6.4$
Atomic mass $=39.93$ g/mol (this is approximate value)
Valence $=\frac{39.93}{20.0}=2$ (it should be an integer)
Atomic mass $=20\times 2=40$ g/mol