NCERT Questions

Class 9
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.

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

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