Calculate the mass of (a) 0.1 mole of KNO3 (b) 1 x 10 23 (c) 112 cm3 molecule of methane of hydrogen at STP

(a) The molar mass of KNO₃  is 101 g/mol. Thus

 1 mole of KNO₃ = 101 g

Therefore 0.1 mole of  KNO₃ = 0.1×1​01 g = 10.1 g

(b) The molar mass of methane (CH₄) is 16 g. As there are 6.022×10²³ molecules in 1 mole of methane, therefore

 6.023×1023 molecules of methane = 16 g of methane

 1 molecule of methane = (16 / 6.022 × 10²³ ) g of methane

 10²³ molecules of methane = (16×10²³ ) / 6.022×10²³ g of methane

 = 2.657 g
(c) 112 cm³ of hydrogen, H₂ at STP.
1 mole of hydrogen at STP occupy 22.4 L or 22400 cm³ volume and mass 2 g.

Mass of 22400 cm³ of hydrogen = 2 g

Mass of 112 cm³ of hydrogen = (2/22400) × 112 = 0.01008 g