Question

One gram atom of an element contains 6.023 × 10²³ atoms. 

1. Find the number of atoms in 8 g oxygen. 

2. Which is heavier, 1 oxygen atom or 10 hydrogen atoms? 

3. Define mole and Avogadro number.

Answer 1

1. 16 g oxygen contains 6.022 × 10²³ atoms 

∴ 8 g oxygen contains \(\frac{6.022\times10^{23}}{2}\) = 3.011 × 10²³  

2. 

1 oxygen atom is heavier.

Mass of 1 oxygen atom = \(\frac{1\times16}{6.022\times10^{23}}\) = 2.66 × 10²³g

Mass of 10 hydrogen atom = \(\frac{10\times1.008}{6.022\times10^{23}}\) = 1.67 × 10²³g

3. One mole is the amount of a substance that contains as many particles or entities as there are atoms in exactly 12 g (or 0.012 kg) of the ¹²C isotope. 

Avogadro number – It is the number of discrete particles present in 1 mole of any substance. (Avogadro number, N_A = 6.022 × 10²³)