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Formula of Magnesium Oxide

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Introduction

Chemistry Practical Assessment: Finding the formula of Magnesium Oxide (Skill 3) Results: Table showing measurements before experiment: Mass of crucible (g) Mass of lid (g) Mass of magnesium (g) Mass of crucible and magnesium (g) 1st try 14.21 11.91 0.9 15.11 2nd try 14.23 11.91 0.9 15.13 3rd try 14.21 11.92 0.8 15.11 Average 14.21 11.91 0.9 15.11 Table showing measurements after experiment: Mass of crucible (g) Mass of lid (g) Mass of contents (g) Mass of crucible and contents (g) 1st try 14.21 11.91 0.07 15.18 2nd try 14.23 11.91 0.06 15.19 3rd try 14.21 11.92 0.05 15.16 Average 14.21 11.91 0.06 15.18 Mass of products and reactants: ? mass of crucible: 14.21g ? mass of crucible and magnesium before heating: 15.11g ? mass of crucible and magnesium after heating: 15.18g ? mass of magnesium before heating: 0.90g ? ...read more.

Middle

Instead of one mole of magnesium combing with one mole of oxygen, nine moles of magnesium combined with one mole of oxygen. This might be due to the fact that there were some mistakes in my experiment, for example, magnesium might not have reacted completely. Sources of error: � While lifting the lid from time to time, the contents inside the crucible might have escaped, so the calculations would be wrong and the mass of the product would be incorrect. � The oxidation reaction of magnesium might not be complete, this will affect the mass of the contents and products. � Sanding the magnesium stripe might be inconsistent which will result in error in the results due to the fact that there are other substances on the magnesium stripe, this will affect the oxidation reaction. � Magnesium in the crucible might also have reacted with other gases in the air, which affects the mass of the products as magnesium didn't only react with oxygen. ...read more.

Conclusion

Table showing actual results: Object Mass (g) Mass of crucible 14.63 Mass of crucible and magnesium 14.87 Mass of crucible and magnesium oxide 15.03 Mass of magnesium used 0.24 Mass of oxygen which has reacted with magnesium 0.16 From the table above, the mass of the crucible and magnesium differ from mines, but it is not of great importance as we used different crucibles and lengths of magnesium. Both our masses of crucible and the contents (magnesium oxide) are the same, with only a difference of 0.15g. However my mass of oxygen which has reacted with magnesium is a lot less than the actual one, by 0.09g. For my empirical, instead of being MgO, it is Mg9O. This shows that nine mole of magnesium combined with one mole of oxygen instead of one mole of magnesium combining with one mole of oxygen. This might be because there are some human errors and mistakes in the experiment. As you can see from my results, the mass of the contents increased after the oxidation reaction. ...read more.

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Response to the question

The essay is presented in a clear and concise format which is impressive. Clear subheadings, and easy to read concise information presented in bullet point form are used. The candidate does not show much thinking around the procedure through the ...

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Response to the question

The essay is presented in a clear and concise format which is impressive. Clear subheadings, and easy to read concise information presented in bullet point form are used. The candidate does not show much thinking around the procedure through the initial method, and seems to stick to a strict correct check-box type method which works well in this instance but will not reach the highest marks by not showing the highest levels of reasoning. They could have for example explained further the changes in the metal observed, and accounted for anything that may have confounded the experiment results beforehand. Overall a very correct and well presented essay which just misses out on the higher levels of thinking required to gain top marks.

Level of analysis

The mass decimal places are not consistent throughout the tables which will lose marks on some exam boards. For example in the first table 0.9 should be presented as 0.90. Aside from this, most decimal points are consistent. Improvements and mistakes observed are accurate, but the candidate could have improved their mark by calculating percentage error.

Quality of writing

In some places the grammar is not completely correct. For example where the students says ' magnesium might not have reacted completely,' which should have included 'the' beforehand to improve the clarity of the sentence. Spelling, punctuation and grammar are otherwise fine. No sources are referenced which are used in the essay.


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Reviewed by skatealexia 27/06/2012

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