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Question 8

Convert into mole.

(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide.

Answer

Mass (in grams) = no. of moles x molecular mass (g/mol)

(a) Molar mass of O2 = 2 x 16 = 32 g/mol
      
Mass = no. of mole x molar mass
      12 = n x 32
      n = 12/3 = 3/8
      n = 0.375 mole 



(b) Given mass = 20 g
      Molar mass of H2O = 2 x 1 + 1 x 16
                                      = 2 + 16 = 18 g/mol
      Mass = no. of mole x molar mass
      20 = n x 18
      n = 20/18 = 10/9
      n = 1.11 mole

(c) Given mass = 22g
      Molar mass of CO2 = 1 x 12 + 2 X 16
                                      = 12 + 32 = 44 g/mol
      Mass = no. of moles x molar mass
      22 = n x 44
      n = 22/44 = ½
      n = 0.5. mole

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