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# Redox titration of copper evaluation

Extracts from this document...

Introduction

Redox Titration of Sodium Thiosulphate against Copper (II) Sulphate My results from this titration can be seen in the table below: Rough 1st 2nd 3rd Final Reading/cm3 29.30 25.25 30.40 28.80 Initial reading/ cm3 05.05 0.80 6.20 4.55 Titre/ cm3 24.25 24.45 24.20 24.25 The concordant results I will be using in my calculation are the titres from my 2nd and 3rd titration as there are within 0.01 cm3 of one another. To calculate the average titre I will use the following method: Average Titre = (24.20 + 25.25) ...read more.

Middle

This is because in each step of the reaction there are 2 moles of each. This will mean that the number of moles of Cu2+ will be the same as the number of moles of S2O32-: n = c x v n of S2O32- = 0.102827763 x 24.225 1000 = 2.491002571 x 10-3 mol n of Cu2+ = 2.491002571 x 10-3 mol Now that I have the number of moles of Cu2+ I can calculate the concentration of it: c = n v c of Cu2+ = 2.491002571 x 10-3 (25/1000) ...read more.

Conclusion

percentage error I need to work out the percentage of the concentration that could be incorrect: Percentage Error = Total uncertainty x Concentration 100 = 0.582759211 x 0.099640102 mol dm-3 100 = � 5.806618723 x 10-4 Now that I have the percentage error I can show the possible errors that there could be in the calculation of the concentration of Cu2+: Highest possible c of Cu2+ = 0.100220763 mol dm-3 Lowest possible c of Cu2+ = 0.09905944 mol dm-3 However I will represent the final concentration I have calculated of the Cu2+as: 0.099640102 � 5.806618723 x 10-4 mol dm-3 0.0996 � 5.81 mol dm -3 (3sf) ...read more.

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3 star(s)

### Response to the question

Overall a good example of calculations needed for experiments. The candidate titles this essay as an 'evaluation,' but rather than an evaluation being present, there is just a set of calculations. For an evaluation the candidate should have included possible ...

### Response to the question

Overall a good example of calculations needed for experiments. The candidate titles this essay as an 'evaluation,' but rather than an evaluation being present, there is just a set of calculations. For an evaluation the candidate should have included possible errors that might have gone wrong with the experiment and how this could have been improved. The candidate should have displayed the method used so that they could have shown where they got this information from about possible errors in a concise format. To do this sort of evaluation displays a higher understanding of every aspect of the practical and these are important skills to develop for the chemistry industry.

### Level of analysis

The decimal places the candidate uses is consistent in the table which means that the candidate could make accurate calculations from them. They also repeated the titrations four times and started off with a trial meaning their results have a greater chance of being reliable. The number of decimal places presented in the end result should ideally be consistent with the number of decimal places used in the table, and in this instance it is not. The candidate does calculate percentage errors which is good to know the margin of possible error in the experiment and how this may affect it, but they do not explain the significance of the results.

### Quality of writing

The candidates spelling, grammar and punctuation are all fine, they highlight their final answers in bold which will also make the answers clear and easier to mark.

Reviewed by skatealexia 08/07/2012

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