Magnesium Oxide Lab. C.s.

Christina Svensson Emery White SCH3UE- 03 Mr. Porter 26th 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 ribbon 2. 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 lid 4. Began to heat the crucible – containing the magnesium spiral, with the lid kept on – carefully, while moving the bunsen burner around under it 5. Removed the lid – to check on the magnesium – with the tong 6. After all the oxygen seemed to be gone, we removed the lid, and heated it strongly for four minutes 7. Cleaned our work area, before measuring the mass of the room tempered crucible, lid and remaining magnesium Quantitative observations: Material/ substance Crucible + lid Crucible+ lid+ magnesium Room tempered magnesium oxide+ crucible and lid Qualitative observations:

Quantitative Observations (±0.01 g) 15.33 g 15.40 g 15.45 g

Substance

Magnesium

Magnesium Oxide

Analysis: 1. Mass of Magnesium used in the reaction: (15.40 g  0.01g )  (15.33g  0.01g )  0.07 g  0.02 g  0.07 g  28.6%

2. Amount of Moles of Magnesium:

0.07  28.6% 24.305 g mol 1  0.00288 mol  28.6%

nmg 

3. Percentage composition of Magnesium: mMg mO  mMg 0.07  28.6%  (0.05  0.02)  (0.07  0.02) 0.07  28.6%  0.12  0.04 0.07  28.6%  0.12  33%  0.583  62%  58.3%  62%

%compMg 

– – – – – – – – – – –

silver solid lustrous metallic malleable opaque solid white clumps ( in a coiled shape) opaque dull powder

4. Theoretical percentage composition of Magnesium: mMg mO+mMg 24.305g  15.999g  24.305g  0.60304  60.304%

%compMg 

5. Mass of Oxygen used in reaction:

(15.45 g  0.01g )  (15.40 g  0.01g )  0.05 g  0.02 g  0.05 g  40%

6. Amount of Moles of Oxygen:

0.05  40% 15.999 g mol 1  0.00313 mol  40%

nO 

7. Percentage composition of Oxygen: mO mMg  mO 0.05  40%  (0.07  0.02)  (0.05  0.02) 0.05  40%  0.12  0.04 0.05  40%  0.12  33%  0.417  73%  41.7%  73%

%compO 

8. Ratio of Magnesium to Oxygen in Magnesium Oxide:

O 0.00288 mol  28.6%  Mg 0.00313 mol  40%  0.920  68.6%  0.920  0.6  Mg1O0.920  0.6 ∑ Empirical formula: MgO Source 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.