The same balance was used to weigh the equipment. This ensured that the uncertainty was the same and that the measurements were accurate.
Equipment
- Roll of magnesium
- Crucible
- Crucible lid
- Pipe clay triangle
- Tripod stand
- Electronic balance
- Bunsen burner
- Tongs
Method
Weigh the empty crucible and lid together. Record the results in a table.
Place magnesium coil into crucible and cover with lid. Place on electronic balance and record results in table.
Set up the equipment as shown in figure 1, leaving some space between the lid and crucible for oxygen to enter, and heat the crucible strongly.
Heat continuously until all the magnesium has burned.
Remove crucible from het using tongs and place on tile to cool.
When cool weigh the crucible and its content again. Record the results in table.
Repeat as necessary.
Results
Observation
After heating the magnesium strongly for few minutes it began to melt and glowed with a bright light. Lifting the lid caused the magnesium to glow even more brightly and white smoke escaped from the crucible. Magnesium turned to a grayish – white powder and no longer glowed with a bright light.
Mass of magnesium = 31.23 – 31.15 = 0.08g
Mass of magnesium oxide = 31.27 – 31.15 = 0.12g
Mass of oxygen combined with magnesium = 0.12 – 0.08 = 0.04g
Analysis
Empirical formula
Empirical formula is MgO.
Error analysis
Percent age uncertainty = error in balance *100
Mass of substance
= 0.01/ 0.08 *100
=12.5%
Conclusion and evaluation
The formula for the metal oxide, magnesium oxide was MgO. This is the formula used universally for magnesium oxide. The ratio or oxygen to magnesium was equal. My answer was rounded down to the nearest whole number as ratios must be in whole numbers, however my hypothesis was proved correct through the results of the experiment. The given formula for magnesium oxide is MgO as the valancy electrons cancel out when reacted to form this.
The design of the experiment stated the variables and how to control them. This gave a clear guideline that I was able to follow so as to achieve these results. The data is accurate as uncertainties were taken into account and the experiment was repeated thrice to ensure accuracy.
The experiment contained a few weaknesses such as the magnesium was burned in air not pure oxygen. This meant it may have also reacted with the nitrogen in air in these conditions to give magnesium nitride. Therefore although the results obtained were MgO, there may be several impurities that assisted in the formation of this formula. the high temperatures may have caused the crucible to react. This would have affected the products formed. Lifting the lid may have lead to some of the products escaping and the product weighing less, therefore the ratio of magnesium to oxygen would be incorrect. Weighing the magnesium oxide while it was still hot would have caused an error as the products would have expanded and they would be heavier than they actually are.
Other factors contributed to the precision of the results obtained. Scraping the magnesium ensured that pure magnesium was used and no other products were formed. Repetition of the experiment enabled a more accurate result to be achieved.
Improvements
The magnesium should be burnt in pure oxygen. This would reduce the formation of products other than magnesium oxide and would give more accurate results.
A stronger crucible should be used so that it doesn’t react during the high temperatures reached when the experiment is going on.
Pure magnesium should be used to prevent the formation of products other than magnesium.