Mass of Magnesium: 0.17g(±0.01 g) Mass of Magnesium oxide: 0.30g(±0.01 g)
Mass of oxygen = (Mass of Magnesium oxide — Mass of Magnesium) = (0.30 — 0.17) = 0.13g
Mass of oxygen = 0.13g
Now that we know that the mass of the oxygen involved in the reaction we can calculate the empirical formula of magnesium oxide, by doing the following procedure.
First of all divide the masses of both Magnesium and Oxygen by their specific Relative atomic mass, as shown below.
(i)Magnesium
Mass involved in the reaction=0.17g
RAM=24.31 g/mol
(ii)Oxygen
Mass involved in the reaction=0.13g
RAM=16.00 g/mol
Now in order to obtain the ratio that basically defines the empirical formula of the compound, you must divide both number calculated in the previous step by the smallest one of them, which in this case is 0.0070.
(i)Magnesium (ii)Oxygen
From the process developed above we can say that the ratio there is between magnesium atoms and oxygen atoms in magnesium oxide is of 1:1, and therefore the empirical formula is MgO, which means there is one oxygen atom for every magnesium atom.
Now to evaluate how reliable our results are we must calculate the percentage error of the practical and the total percentage of uncertainty.
Percentage error
This percentage is calculated by adding up the percentage error of the ratio between magnesium and oxygen.
a) (for magnesium) b) (for magnesium)
The total percentage error of this practical was of 15%
Total percentage uncertainty
This percentage is calculated by the addition of the percentage uncertainty of the masses of magnesium and of oxygen.
Percentage uncertainty of the mass of Magnesium
Uncertainty: ±0.01g
Mass of magnesium: 0.17g
Percentage uncertainty = 5.9%
Percentage uncertainty = 5.9%
Percentage uncertainty of the mass of Oxygen
Uncertainty: ±0.01g
Mass of oxygen: 0.13g
Percentage uncertainty = 7.7%
Percentage uncertainty = 7.7%
Total Percentage uncertainty = 7.7%+5.9%=13.6%
The total percentage uncertainty for this practical was of 13.6%.
Having already calculated the percentages we can say that the results are reliable, since both of the percentage weren’t very high.
CONCLUSION:
- The empirical formula for magnesium oxide is MgO, the ratio between oxygen atoms and magnesium atoms is of 1:1, which means there is one atom of magnesium for every atom of oxygen.
- Magnesium needs heat in order to achieve the activation energy needed to react with oxygen to form magnesium oxide.
EVALUATION:
If we look at the percentage error of the experiment and the total uncertainty percentage we can see that the first one is higher than the second one, which means that there were random errors in the development of the practical which affected the precision of our results.
The presence of the previously mentioned random errors can be easily explained by understanding the method used to develop the practical, since the oxygen was allowed to go into the crucible by taking the lid off, so when this occurred some of the newly formed magnesium oxide escaped out of the crucible and therefore some of it wasn’t registered in the mass of magnesium oxide.
To avoid the presence of the random errors I can suggest to improvements for this practical, first of all the use of better or more specialized equipment that allows us to have a more controlled way of introducing oxygen into the crucible where the magnesium is being heated. And secondly I suggest repeating the practical at least 2 times in order to calculate an average of the results so the possibility of random errors is reduced to its minimum.