Question

calculate the number of molecules contained 0.7kg in oxygen under normal conditions

Answer 1

Given : weight of oxygen gas is 0.7 kg under normal conditions.

To find : The number of molecules of oxygen gas in 0.7 kg mass of oxygen gas.

Solution : first we should find out number of moles in 0.7 kg of oxygen gas.

no of moles = weight in gram/molecular weight of oxygen gas

= (0.7 × 1000)g/(32g/mol)

= 700/32 = 21.875 moles

no of molecules = no of moles × Avogadro's number

= 21.875 × 6.023 × 10²³

= 131.753125 × 10²³

= 1.31753125 × 10^25 ≈ 1.32 × 10^25

Therefore number of molecules is 1.32 × 10^25