Ncert Exercises & Solutions

Calculate the number of atoms in 39.4 g gold. The molar mass of gold is 197 g $m o l e^{- 1} .$

Hint: The no. of atoms depends on the no. of moles of the substance.

Step 1: Find the no. of molecules in 1 mole.

We know that,

Molar mass = Mass of Avogadro's number of atoms (Molecules) = Mass of 6.023

\times 10^{23}

atoms

Step 2: Find the no. of molecules in the given mass.

Given, the molar mass of gold = 197 g/mol
Now,

∴

197 g of gold contains=6.023

\times 10^{23}

atoms

∴

1 g of gold contain

= \frac{6.023 \times 10^{23}}{197}

atoms

∴

39.4 g of gold contains

= \frac{6.023 \times 10^{23} \times 39.4}{197} \Rightarrow 1.20 \times 10^{23}

atoms