In this chemical reaction, how many grams of al2o3 will be produced if 375 grams of al react completely? express your answer to three significant figures.

≈ 708 ( to 3 s.f.)

Working Out:

First we have to establish a balanced chemical equation that defines the reaction

       4 Al     +    3 O₂    →    2 Al₂O₃

Now, mole =  mass ÷ molar mass

∴ If the mass of Al in the reaction = 375 g

              then the # of moles of Al =  375 g  ÷  27 g/mol

                                                        =  13.889 mol

Also, the mole ratio between Al and Al₂O₃  is  2 : 1  (4 : 2).

As such if moles of Al = 13.889 mol

then #  of moles of Al₂O₃ =  13.889 mol ÷ 2

                                         = 6.944 mol

Since mass = mole × molar mass

Then mass of Al₂O₃ = 6.944 mol × ((27 × 2) + (16 × 3)) g/mol

                                 = 6.944 mol × 102  g/mol

                                 = 708.288 g

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