1.29: Calculate Reacting Masses Using Experimental Data and Chemical Equations

REACTING MASSES: Chemical equations can be used to calculate the Moles or Masses of Reactants and Products

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• Use information from the question to find the Mole of a Substance / Reactant
• Identify the ratio of the substance and reactants and find the Moles of others
• Apply Mole calculations to find answer

Example 1:

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Calculate the Mass of Magnesium Oxide that can be made by Completely Burning 6 g of Magnesium in Oxygen

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Magnesium (s)  + Oxygen (g)  →   Magnesium Oxide (s)   SYMBOL EQUATION:     2Mg     +     O2       →       2MgO RELATIVE FORMULA MASS:    Magnesium : 24             Magnesium Oxide : 40 STEP 1 - Calculate the Mol of Magnesium Used in Reaction                Moles = Mass ÷ Mr                                       Moles = 6 ÷ 24 = 0.25 STEP 2 - Find the Ratio of Magnesium to Magnesium Oxide using Chemical Equation                                         Magnesium               Magnesium Oxide                Mol                            2                                      2                Ratio                         1                                      1                Mol                          0.25                                 0.25                Mol of Magnesium Oxide = 0.25 STEP 3 - Find the Mass of Magnesium Oxide                Moles of Magnesium Oxide = 0.25                Mass = Moles x Mr                                       Mass = 0.25 x 40 = 10                                                              Mass of Magnesium Oxide Produced = 10 g

Example 2:

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Calculate the Mass, in Tonnes, of Aluminium that can be produced from 51 Tonnes of Aluminium Oxide

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Aluminium Oxide (s)  →   Aluminium (s)   +   Oxygen (g) SYMBOL EQUATION:     Al2O3     →       2Al       +       3O2 RELATIVE FORMULA MASS:  Aluminium : 27    Oxygen : 16    Aluminium Oxide : 102 1 Tonne = 106 g STEP 1 - Calculate the Mol of Aluminium Oxide Used               Mass of Aluminium Oxide in Grams = 51 x 106 = 51000000                 Moles = Mass ÷ Ar                               Moles = 51000000 ÷ 102 = 1000000 STEP 2 - Find the Ratio of Aluminium Oxide to Aluminium using Chemical Equation                                         Aluminium Oxide         Aluminium                Mol                            1                                     2                Ratio                         1                                     2                Mol                      1000000                         2000000                Mol Aluminium = 2000000 STEP 3 - Find the Mass of Aluminium                Moles of Aluminium = 2000000                Mass = Moles x Mr                          Mass = 2000000 x 27 = 54000000                Mass in Tonnes = 54000000 ÷ 106 = 54 Tonnes                                                                Mass of Aluminium Produced = 54 Tonnes