Discovering the formula of MgO

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Zara Alam

Report 6: Reaction between Magnesium and Oxygen


The aim of our experiment was to observe the effect of burning pure Magnesium (Mg) in oxygen (O2) and to confirm the chemical formula of magnesium oxide by comparing the masses of pure solid magnesium (prior to any reaction) and magnesium oxide solid after a reaction between magnesium and oxygen from the air when heated from a Bunsen burner in a crucible. Using molar masses of both magnesium and oxygen, an expected percent composition, by mass, was found and compared to our experimental results. 

Theory: Magnesium oxide is easily made by burning magnesium ribbon which oxidizes in a bright white light, resulting in a powder.

2 Mg(s) + O2 (g)  2 MgO (s)                      ΔH = −1204 kJ

Theoretical work:

% composition of oxygen in Mg2O= 16.00/ ((24.01*2) +16) =25.0%

% composition of oxygen in MgO=16.00/ (24.01+16) =40.0%

% composition of oxygen in MgO2=16.00/(24.01(16.00*2))=57.1%

Prediction: Weight of material would increase when magnesium burns.


(i)Independent variable: Mass of Magnesium ribbon

(ii)Dependent variable: Mass of Magnesium Oxide

The independent variable will be the mass of magnesium ribbon, this is because the mass of the product i.e. Magnesium Oxide, depends on how much Magnesium is added. The dependent variable will be the mass of Magnesium Oxide, this is a measured variable as the mass of oxygen can be calculated and will enable us to determine the formula for Magnesium Oxide.

Controlled variables:

  1. Container used
  2. Surface area of Magnesium
  3. Concentration of oxygen in the container
  4. Temperature of flame

Controlling variables:

  1. A crucible with a lid is used and is filled with a layer of filter paper, in order to allow combustion in a closed environment, preventing the loss of Magnesium oxide powder.
  2. Magnesium ‘ribbon’ will be used in all cases.
  3. The experiment is performed in the same laboratory on the same day i.e., the atmospheric conditions and oxygen concentration will be the same.
  4. The same Bunsen burner was used every time, with the air hole completely open.
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Apparatus and chemicals:

  1. Crucible with lid                
  2. Bunsen burner
  3. Tripod                              
  4. Tongs
  5. Balance                            
  6. Pipe clay triangle
  7. Beaker
  8. Magnesium ribbon


  • Inhalation of magnesium oxide fumes can cause  therefore ensure that the room is well ventilated.
  •  The bright flame of MgO is very hard to extinguish and it emits a harmful intensity of UV light therefore do not look ...

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