Chapter U4.75, Problem 1TAI

Interpretation Introduction

Interpretation:

The use of mass in counting the number of small objects needs to be explained.

Concept introduction:

Mass is the amount of matter present in a substance. It is proportional to the quantity of the substance which is not changed by any external parameters like temperature, pressure, etc.

Answer to Problem 1TAI

Mass is one useful unit to count larger number of small objects for example atoms of any element. Counting atoms one by one is not possible, but this problem can be addressed by using mass.

Explanation of Solution

If $6.023\times {10}^{23}$ number of S atoms needs to be counted, and it can be easily done by taking the mass of the atoms. Mass of $6.023\times {10}^{23}$ number of S atoms is the gram atomic mass which is 32 g.

Similarly, if the number of N atoms in 63 g HNO₃ needs to be determined,then counting the N atoms is not possible. Only one simple calculation can help to find out the number of N atoms in 63 g HNO₃. Molar mass of nitric acid is 63 g/mol. So there will be $6.023\times {10}^{23}$ number of N atoms.

In the same way, if one requires $6.023\times {10}^{23}$ number of N atoms,one can just weigh 14 g of N, as molar mass of N is 14 g/mol.