Name: Law of Multiple Proportions
Uploaded: 2019-07-19
Duration: 6 min 43 s
Description: The Law of multiple proportions is applicable only when two elements combine to form two or more compounds. Watch this video to know how this law is applicable.

Question

State Dulong Petit's law. Describe how the atomic mass of an element is determined by the use of the law. A certain metal oxide contains

60 %

of oxygen. The specific heat of the metal is

0.401

. Calculate the exact atomic mass, equivalent mass and valency of the metal.

Accepted Answer

The French Scientists Dulong and Petit studied the relationship between specific heat and the atomic mass of elements. 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 :

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

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.

Consider,

$100 g of metal oxide % of oxygen = 60 % of metal = 100 - 60 = 40 Mass of oxygen = 60 g Mass of metal = 40 g Equivalent mass of metal = \frac{Mass of element \times 8}{Mass of oxygen in oxide} = \frac{40 \times 8}{60} = 5.33 By Dulong Petti' s law, Atomic mass \times Specifi heat ≃ 6.4 Atomic mass ≃ \frac{6.4}{Specifi heat} ≃ \frac{6.4}{0.401} = 15.96 Now, Valency = \frac{Atomic mass}{Equivalent mass} = \frac{15.96}{5.33} = 2.99 = 3 .$

State Dulong Petit's law. Describe how the atomic mass of an element is determined by the use of the law. A certain metal oxide contains $60 %$ of oxygen. The specific heat of the metal is $0.401$ . Calculate the exact atomic mass, equivalent mass and valency of the metal.

Important Questions on Basic Concepts Atoms & Molecules

Learn and Prepare for any exam you want !

State Dulong Petit's law. Describe how the atomic mass of an element is determined by the use of the law. A certain metal oxide contains 60% of oxygen. The specific heat of the metal is 0.401. Calculate the exact atomic mass, equivalent mass and valency of the metal.

Important Questions on Basic Concepts Atoms & Molecules

Learn and Prepare for any exam you want !

State Dulong Petit's law. Describe how the atomic mass of an element is determined by the use of the law. A certain metal oxide contains $60 %$ of oxygen. The specific heat of the metal is $0.401$ . Calculate the exact atomic mass, equivalent mass and valency of the metal.