Question

1. How many molecules of barium hydroxide, Ba(OH)2 are there in 21.9 grams of

Answer 1

Answer: $7.7\times 10^{22}$ molecules of $Ba(OH)_2$

Explanation:

According to avogadro's law, 1 mole of every substance occupies 22.4 L at STP and contains avogadro's number $6.023\times 10^{23}$ of particles.

To calculate the moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text {Molar mass}}=\frac{21.9g}{171g/mol}=0.128moles$

1 mole of $Ba(OH)_2$ contains =  $6.023\times 10^{23}$ molecules

0.128 mole of $Ba(OH)_2$ contains =  $\frac{6.023\times 10^{23}}{1}\times 0.128=7.71\times 10^{22}$ molecules

Thus there are $7.7\times 10^{22}$ molecules of $Ba(OH)_2$