Question

Chromium is obtained by heating chromium(III) oxide with carbon. Calculate the mass percent of chromium in the oxide, and then use this value to calculate the quantity of Cr₂O₃ required to produce 620. kg of chromium metal.

Answer 1

The formula of chromium(III) oxide is Cr₂O₃

Molar mass of Cr₂O₃ is = (2xAt.mass of Cr ) + ( 3xAt.mass of O )

                                      = ( 2x 52) + (3x16)

                                      = 152 g/mol

Molar mass of Cr in Cr₂O₃ is = 2xAt.mass of Cr

                                              = 2x52

                                             = 104 g/mol

Mass percentage of chromium is = [( mass of Chromium / mass of chromium oxide) x100 ]

                                                    = (104 / 152) x100

                                                    = 68.4 %

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The balanced reaction is Cr₂O₃ + 3C 2Cr + 3CO

According to the above balanced equation ,

1 mole of Cr₂O₃ produces 2 moles of Cr

                             OR

152 g of Cr₂O₃ produces 2x52 g of Cr

                               OR

152 kg of Cr₂O₃ produces 2x52 kg of Cr

M kg of Cr₂O₃ produces 620 kg of Cr

M = (152 x 620 ) / (2x52)

   = 906.1 kg of Cr₂O₃

Therefore the mass of Cr₂O₃ required is 906.1 kg