Question

State and explain Dulong and Petit's law. Define atomic mass. The specific heat of an element is

0.057

0.057. Its equivalent mass is

37.8

. What is it's exact atomic mass ?

Accepted Answer

Dulong and Petit's law states that the product of the relative atomic mass of an element and its specific heat is approximately equal to $6.4$ for all solid elements at ordinary temperature (except carbon-silicon, boron & beryllium). This product is called atomic heat. Mathematically, it can be stated that :

Relative atomic mass x Specific heat $≃$ $6.4$ .

The specific heat is usually expressed in calories per degree per gram of the element. If however, the specific heat is expressed in joule, then relative atomic mass X specific heat $≃$ $26.8$ .

Dulong and Pet's law can be applied to determine the approximate relative atomic mass of an element. In order to find out the correct relative atomic mass of an element, the following steps are adopted.

The approximate relative atomic mass of the element is calculated from the known specific heat of the element with the help of Dulong and Petit's law.

The approximate relative atomic mass = $\frac{6.4}{Specific heat}$ .

The equivalent mass of the element is determined from the experiment.

The approximate relative atomic mass is divided by the equivalent mass to get an approximate valency.

Relative atomic mass (approx) = Equivalent mass x Valency (approx)

The approximate valency is converted to the nearest whole number.

The correct relative atomic mass of the element is calculated from the product of equivalent mass and the valency (whole number).

Relative atomic mass = Equivalent mass x Valency.

The approximate atomic mass of the metal = $\frac{64}{0.057} = 112.28$

The approximate valency of the metal = $\frac{Approx . atomic mass of element}{Equivalent mass of the element} = \frac{112.28}{37.8} = 2.97 and converted to the nearest whole number valency 3 . Now the exact atomic mass of the element = Equivalent mass \times Valency = 37.8 \times 3 = 113.4 .$

The atomic mass or the relative atomic mass of an element is a number that expresses how many times the mass of one atom of the clement is heavier than the mass of one atom of hydrogen.

The atomic mass of an element = $\frac{Mass of 1 atom of the element}{Mass of 1 atom of hydrogen}$ .

Odisha Board Solutions for Chapter: Basic Concepts Atoms & Molecules, Exercise 2: QUESTIONS

Odisha Board Chemistry Solutions for Exercise - Odisha Board Solutions for Chapter: Basic Concepts Atoms & Molecules, Exercise 2: QUESTIONS

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