Atomic mass is the mass of an atom as measured in atomic mass units. Although standards for calculating the mass of atoms were used in the past, currently scientists use the atomic mass unit. It is the average relative mass of an atom of the element as compared to the mass of C-12 isotope taken as 12 atomic mass units. In fact, atomic mass tells how may times an atom is heavier than 12th part of C-12 isotope.

Atomic mass = $\frac{Average\ mass\ of\ an\ atom\ of\ element}{\frac{1}{12} \times mass\ of\ C-12\ atom}$

Atomic mass = Atomicity $\times$ Atomic mass

Atomic mass is used in virtually all chemical reactions. Chemist often writes atomic masses as ordinary figures when used in simple calculations and equations.

## Atomic Mass Formula Problems

Some of the solved problems based on Atomic Mass Formula is given below.

Question 1: A certain divalent metal salt solution is Electrolyzed in series with a silver coulometer. The weight of silver and the metal deposited are respectively 0.52 gram and 0.27 gram. Given that the equivalent mass of silver is 108, what is the atomic mass of the metal?
Solution:
Some amount of current deposits = some number of g-equivalent of meals.

0.52g of Ag = 0.27g of metal

108g of Ag = $\frac{0.27}{0.52}$ $\times$ 108

= 56g of metal

Thus, the equivalent weight of metal = 56

Since,

Equivalent mass $\times$ Valency = atomic mass

56 $\times$ 2 = 112

Hence, the atomic mass of the metal is 112.

Question 2: An element (X) having equivalent mass E forms a general oxide XmOn. What is the atomic mass of that element?
Solution:
The compound XmOn has n $\times$ 16 parts of oxygen combining with m $\times$ Atomic mass of X

Therefore, 8 parts of oxygen combines with X = $\frac{m \times Atomic\ mass}{n \times 16}$ $\times$ 8

E = $\frac{m \times Atomic\ mass}{n \times 2}$

(or) Atomic mass = $\frac{2E \times n}{m}$

Hence, the atomic mass of the given element is $\frac{2En}{m}$.