1.36: Practical: Know How to Determine the Formula of a Metal Oxide by Combustion (E.g. Magnesium Oxide) or by Reduction (E.g. Copper (II) Oxide)

METAL OXIDE: When a Metal Reacts With and Gains Oxygen

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COMBUSTION OF METAL OXIDES

Diagram showing the Apparatus needed to find the Formulae of a Metal Oxide by Combustion

METHOD: Measure the mass of crucible with lid Add sample of Metal into crucible and measure mass with lid (calculate the mass of Metal by subtracting the mass of empty crucible) Strongly heat the crucible over a bunsen burner for several minutes Frequently lift the lid to allow sufficient Air into the crucible for the Metal to fully oxidise without letting Magnesium Oxide escape Continue heating until the mass of crucible remains constant (maximum mass), indicating that the reaction is complete Measure the mass of crucible and contents (calculate the mass of Metal Oxide by subtracting the mass of empty crucible)

WORKING OUT EMPIRICAL FORMULA / FORMULAE: Mass of Metal: Subtract mass of crucible from Metal and mass of empty crucible Mass of Oxygen: Subtract mass of Metal used from the mass of Magnesium Oxide STEP 1 - Divide each of the Two Masses by the Relative Atomic Masses of Elements STEP 2 - Simplify the Ratio                                     Metal            Oxygen               Mass               x                       y               Mole              x / Mr               y / Mr                                      = a                   = b                                        Ratio                a          :           b STEP 3 - Represent the Ratio into the ‘ Metal O ‘ (e.g, MgO)

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REDUCTION OF METAL OXIDES

Diagram showing the Apparatus needed to find the Formulae of a Metal Oxide by Reduction

METHOD: Measure mass of Metal Oxide Use a clamp to hold boiling tube horizontally, and place Metal Oxide at the end of the tube Heat using a bunsen burner until Metal Oxide completely changes colour, indicating that all Oxygen has been reduced Measure mass of the remaining Metal Powder

WORKING OUT EMPIRICAL FORMULA / FORMULAE: Mass of Metal: Measure mass of remaining Metal Powder Mass of Oxygen: Subtract mass of the remaining Metal Powder from the mass of Metal Oxide STEP 1 - Divide Each of the Two Masses by the Relative Atomic Masses of Elements STEP 2 - Simplify the Ratio                                     Metal            Oxygen               Mass               a                       b               Mole              a / Mr               b / Mr                                      = x                   = y                                        Ratio                x          :           y STEP 3 - Represent the Ratio into the Form ‘ xO ‘ (e.g, MgO)