Christina Svensson Emery White SCH3UE- 03 Mr. Porter th 26 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: – Cruci ucible ble an and li lid – Crucible to tong – Elec Electr tron onic ic bala balanc ncee – Retort stand – Ring clamp – Wire gauze – Clay tr triangle – Bunsen burner – Magnesi esium ri ribbon Procedure: 1. Obtained Obtained and got out equipment equipment ready before obtaini obtaining ng the magnesi magnesium um ribbon ribbon 2. Measured Measured the mass mass of the the crucible crucible and the the lid- after cleaning cleaning and drying drying it. it. 3. Placed the the magnesium magnesium spiral spiral into into the crucible crucible and measured measured the the mass of the the crucible, crucible, magnesium spiral and the crucible lid 4. Began to heat heat the crucible crucible – containing containing the the magnesium magnesium spiral, spiral, with with the lid lid kept on – carefully, while moving the bunsen burner around under it 5. Removed the lid lid – to check on the magnesi magnesium um – with with the tong 6. After all all the oxygen oxygen seemed seemed to be gone, we removed removed the the lid, and heated heated it strong strongly ly for four minutes 7. Cleaned our our work area, area, before before measuring measuring the mass mass of the room room tempered tempered crucible, crucible, lid 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 Mass of Magne Magnesiu sium m used used in the react reaction ion:: (15.40 g 0.01 g) (15.33 g 0.01 g)
0.07 g 0.02 g
0.07 g 28.6%
2. Amount Amount of Moles Moles of Magnes Magnesium ium:: nmg
0.07 0.07 28.6 28.6% % 24.305 gmol mol 1 0.0028 0.00288 8 mol 28.6% 28.6%
3. Percent Percentage age comp composi ositio tion n of Magne Magnesiu sium: m: %compMg
mMg mO mMg
0.07 0.07 28.6 28.6% % (0.0 (0.05 5 0.0 0.02) (0.0 (0.07 7 0.02 0.02)) 0.07 0.07 28.6 28.6% % 0.12 0.12 0.04 0.04 0.07 0.07 28.6 28.6% %
0.12 0.12 33% 33% 0.583 3 62% 62% 0.58
58.3 58.3% % 62% 62%
silver solid lustrous metallic malleable opaque solid whit whitee clum clumps ps ( in in a coile coiled d sha shape) pe) opaque dull powder
4. Theoretical Theoretical percentage percentage composition composition of Magnesium: Magnesium: %compMg
5.
mMg mO+mMg 24.305g 15.999 15.999g g 24.305 24.305g g
0.60304
60.304%
Mass of Oxygen used in reaction: (15.45 g 0.01 g) (15.40 g 0.01 g)
0.05 g 0.02 g
0.05 g 40%
6. Amoun Amountt of Mole Moless of Oxyge Oxygen: n:
nO
0.05 0.05 40% 40% 15.999 gmol mol 1 0.0031 0.00313 3 mol mol 40% 40%
7. Percent Percentage age compos compositi ition on of Oxygen: Oxygen: %compO
mO mMg mO
0.05 .05 40% 40% (0.0 (0.07 7 0.02) .02) (0.0 (0.05 5 0.0 0.02) 0.0 0.05 40% 40% 0.12 0.12 0.04 0.04 0.0 0.05 40% 40%
0.12 .12 33% 33% 0.417 7 73% 73% 0.41
41.7 41.7% % 73% 73%
8. Ratio Ratio of Magne Magnesiu sium m to Oxygen Oxygen in Magnes Magnesium ium Oxide Oxide::
O Mg
0.00288 mol 28.6% 0.00313 mol 40%
0.92 0.920 0 68.6% 68.6%
0.92 0.920 0 0.6 0.6
Mg1O 0.920 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 not all oxygen, other substances might have mixed with our compound, co mpound, which might lead to a misleading result. The third source of error – an error we did not experience ourselves o urselves – 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 wou ld 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 han ds will change the mass of crucible as a s 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.
