Christina SvenssonEmery WhiteSCH3UE- 03

Mr. Porter26th January 2009

Magnesium Oxide – Simplest Formula and Percentage Composition

Purpose:To prepare a sample of magnesium oxide and determine the simplest formula and percentage composition for the compound

Apparatus/ Materials:- Crucible and lid- Crucible tong- Electronic balance- Retort stand- Ring clamp- Wire gauze- Clay triangle- Bunsen burner- Magnesium ribbon

Procedure:1. Obtained and got out equipment ready before obtaining the magnesium ribbon2. Measured the mass of the crucible and the lid- after cleaning and drying it.3. Placed the magnesium spiral into the crucible and measured the mass of the crucible,

magnesium spiral and the crucible lid4. Began to heat the crucible – containing the magnesium spiral, with the lid kept on –

carefully, while moving the bunsen burner around under it5. Removed the lid – to check on the magnesium – with the tong6. After all the oxygen seemed to be gone, we removed the lid, and heated it strongly for

four minutes7. Cleaned our work area, before measuring the mass of the room tempered crucible, lid and

remaining magnesium

Quantitative observations:

Material/ substanceQuantitative Observations(±0.01 g)

Crucible + lid 15.33 g

Crucible+ lid+ magnesium 15.40 gRoom tempered magnesium oxide+ crucible and lid

15.45 g

Qualitative observations:Magnesium Strip Lustrous, long, thin, solid, bendable, flexible,

silver, opaqueMagnesium after removing lid of crucible Black with white, textured speckles all over

the surface, still solid and in spiral shapeMagnesium after 30 minutes of heating Slightly more wilted spiral, gray with white,

textured, elevated specklesMagnesium after removing and poking it Brittle, breaks easily and turns to grey powder

Analysis:1. Mass of Magnesium used in the reaction:

2. Amount of Moles of Magnesium:

3. Percentage composition of Magnesium:

4. Theoretical percentage composition of Magnesium:

5. Mass of Oxygen used in reaction:

6. Amount of Moles of Oxygen:

7. Percentage composition of Oxygen:

8. Ratio of Magnesium to Oxygen in Magnesium Oxide:

∑ Empirical formula: MgOSource of Error:

In this experiment we experienced two types of error, while seeing other experience the third. Our first source of error was lifting the lid of systematically- to check if the magnesium and the oxygen were done reacting. This might have caused mistakes in the calculations, making the oxidation go slower by supplying the MgO with more oxygen as we kept lifting of the lid.

Since we kept taking the lid of to check on the MgO, the air must have mixed with our compound, making our final product contained and impure. Since the air is not all oxygen, other substances might have mixed with our compound, which might lead to a misleading result.

The third source of error – an error we did not experience ourselves – was the smoke coming out of the crucible. We were extra careful heating it up, knowing that gas might be lost in the smoke, hence; lead to the wrong answer. Another error is the temperature of the crucible while measuring the mass: if it is too hot, the high temperature will lead to an increase in mass, making the result incorrect and imprecise. We waited until the crucible was room tempered before we massed it to get the most accurate number possible.

Another source of error – which would considered a minor error in this experiment – is touching the crucible with our bare hands; the crucible and cover should always be held by the tong, because the oil from hands will change the mass of crucible as oil adheres to porcelain.

Discussion:In this experiment we prepared a sample of magnesium oxide, and used the results – after oxidising the magnesium – to determine the simplest formula for Magnesium Oxide: MgO. We also calculated the percentage composition of both magnesium and oxygen. The percentage composition of magnesium was theoretically calculated to be 60.304 %, but the actual value (the results from our lab) was 58.3 % ± 62 %, indicates a 2.004 % error in our results. Even with these inaccurate results, we were able to determine the simplest formula of magnesium oxide, through calculating the ratio between the elements. MgO is the correct formula for magnesium, is we calculated.

Conclusion: In this experiment we managed to calculate the empirical formula of magnesium oxide, using our ratio and percentage composition. Even with an imprecise percentage composition of magnesium – there was an error of 2.004 % - we were able to succeed in completing the purpose of this lab: To prepare a sample of magnesium oxide and determine the simplest formula and percentage composition for the compound.