6.3 X10 6.3 X10
Mg O
- 1
Magnesium oxide is made up of a ratio by mass of approximately 1:1 Magnesium to Oxygen, giving up an empirical formula of MgO.
Before adding water Magnesium oxide had a white appearance resembling bird droppings. This changed it to grey color like a cigarette ash.
Percentage Error = (moles of Oxygen- moles of Mg) x100%
Moles of oxygen
= (6.3 X10- 6.7 X10) x100%
6.3 X10
= 0.6%
Conclusion and evaluation:
The empirical formula obtained experimentally from the lab defers from the theoretical empirical formula, proving that the results of the experiment do not support the theoretical assumptions about the formula for magnesium oxide. To determine experimental mole ratio, first the average number moles of each element was found. The average beginning amount of magnesium, 0.18g, was divided by 24.31g Mg to get the average number of moles of magnesium in the reaction. Then the average amount of oxygen, 0.10g, was divided by 16g O to get the average moles of oxygen in the reaction. From these numbers the experimental mole ratio was calculated as 1.1:1(Refer to Results for complete calculations). The theoretical empirical formula for Magnesium Oxide was Mg2.4O while the experimental empirical formula was MgO.
Because the theoretical mole ratio differed from the experimental mole ratio, there is a mole ratio percent error. To find the mole ratio percent error, the Oxide as 2 magnesium atoms per 2 oxygen atoms. This theoretical ratio is 2:2which equals 1:1.
From the Experimental empirical formula, the experimental percent composition was determined to be 65.2% magnesium in the magnesium oxide and 34.5%oxygen in the magnesium oxide. These numbers differ from the theoretical percent composition, as the theoretical percent composition was 60.3% magnesium and 39.7%oxgyen. The percent error in the experimental percent compositions for both magnesium and oxygen were calculated using the theoretical percent compositions for magnesium and oxygen, and the experimental percent compositions for these elements, and then plugging these numbers into the percent error formula. The percent error for magnesium was 8.6%, with the percent error of the oxygen being 13.1 %.( Refer to percent error under results for complete calculations)
There are many possible reasons for the difference of the theoretical empirical formula and the experimental empirical formula. The difference between the empirical formulas lies in the number recorded throughout the lab, including mass of empty crucible and lid, the initial mass of the magnesium, final mass of magnesium oxide, the difference in weight, or mass of oxygen combined with magnesium in the combustion reaction. A variety of factors influenced these numbers possibly causing a measured mass to be, in fact, incorrect.
One variable is the contaminants left in the crucible from the previous trials. If not thoroughly washed and cleaned, the crucible could have a small amount contaminant in it that would make virtually all of the mass measurements incorrect. Another variable is the heat of the flame used to heat the crucible. Whether the magnesium is burned at a lower temperature for a longer period of time, or a higher temperature for a shorter period of time, may affect the oxidation of the magnesium, which in turn would affect the final mass of the magnesium oxide and therefore the calculated mass of the combined oxygen. Also, although the crucible was taken off the flame only when the magnesium inside looked fully oxidized, and therefore altered the ratio of magnesium to oxygen in the resulting magnesium oxide, because of the amount of magnesium which was not chemically combined with oxygen.
Improvements may be made to the lab to lessen the margin for error. The shape of the metal could be standardized to lessen the possibility for leftover unoxidized magnesium. If the magnesium was in smaller particles, the greater surface area might allow a more complete oxidation process since there would be more surface area for the oxygen to chemically react with. Also a way to ensure complete oxidation of the magnesium would be beneficial. Although stirring the magnesium oxide to check for any unoxidized magnesium would probably remove some magnesium oxide on the stirring instrument, maybe the crucible could simply be left on the flame for an additional period of time to lessen the chance for unoxidized magnesium.