Question

One mole of oxygen gas at STP is equal to :

(i) 6.022 × 10²³ molecules of oxygen

(ii) 6.022 × 10²³ atoms of oxygen

(iii) 16 g of oxygen

(iv) 32 g of oxygen

Answer 1

(i) 6.022 × 10²³ molecules of oxygen

(iv) 32 g of oxygen

Explanation:

One mole of oxygen gas at STP is equal to 6.022 × 1023 molecules of oxygen.

The number of moles is given by the following formula,

Moles = ${\displaystyle \frac{\text{Mass}}{\text{Molar mass}}}$  ......(1)

The number of moles of $$\mathrm{O}{\phantom{A}}_2$$ is calculated by using equation (1) as follow.

Moles of O₂ = ${\displaystyle \frac{16g}{\frac{32g}{mol}}}$ = 0.5 mol

The number of molecules can be calculated as, number of moles = ${\displaystyle \frac{\text{Number of molecules}}{\text{Avogadro's number}}}$  ......(2)

On substituting the values in the above equation:

0.5 mil = ${\displaystyle \frac{\text{Number of molecules}}{6.022\times {10}^{23}}}$

Number of molecules = 0.5 × 6.022 × 10²³

The number of moles is given by the following formula,

Moles = ${\displaystyle \frac{\text{Mass}}{\text{Molar mass}}}$  ......(1)

The number of moles of $$\mathrm{O}{\phantom{A}}_2$$ is calculated by using equation (1) as follows,

Moles of $$\mathrm{O}{\phantom{A}}_2$$ = ${\displaystyle \frac{32g}{\frac{32g}{mol}}}$ = 1 mol

The number of molecules can be calculated as, number of moles = ${\displaystyle \frac{\text{Number of molecules}}{\text{Avogadro's number}}}$  ......(2)

On substituting the values in the above equation:

1 mol = ${\displaystyle \frac{\text{Number of molecules}}{6.022\times {10}^{23}}}$

Number of molecules = 1 × 6.022 × 10²³