NCERT Question 8 - Chapter 3 Class 9 - Atoms And Molecules

Convert into mole.

(a) 12 g of oxygen gas

(b) 20 g of water

(c) 22 g of carbon dioxide.

Answer

We know that,

Number of moles of a substance = Given mass of the substance / Molar mass of the substance

(a) 12 g of oxygen gas

Given mass of O ₂ = m = 12g

Molar Mass of O ₂ = M = 32g

We know that,

Number of moles of a substance = Given mass of the substance / Molar mass of the substance

= m/M

= 12g / 32g

= 6 /16  moles

                                     = ⅜ moles

(b) 20 g of water

Given mass of H ₂ O = m = 20g

Molar Mass of H ₂ O = M = 18g

We know that,

Number of moles of a substance = Given mass of the substance / Molar mass of the substance

= m/M

= 20g/18g

= 10/9  moles

(c) 22 g of carbon dioxide

Given mass of CO ₂ = m = 22g

Molar Mass of CO ₂ = M = 44g

We know that,

Number of moles of a substance = Given mass of the substance / Molar mass of the substance

= m/M

= 22g/44g

= 1/2  moles

                                     = 0.5 moles