IB CHEMISTRY INTERNAL ASSESSMENT
Determination of the empirical formula of copper sulphate (SL/HL)
This experiment will be used to assess you on skills: DCP and CE.
A ‘2’ will be awarded if the following aspects for each criterion have met been met completely:
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DCP
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CE
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Records data which is appropriate to the investigation i.e. any measurements which are
needed to calculate the empirical formula. Include units and uncertainties.
Record any qualitative data (e.g. observations) which you think are useful and would
help the interpretation of the results.
Under the heading “Calculations’ process your raw data correctly including correct
significant figures.
Propagate uncertainties (HL only). SL: indicate a % error considering the apparatus
used
Present your calculations in a logical manner.
Write a conclusion and explain how you have arrived at your conclusion i.e. how you
have interpreted the data you have collected.
Compare your value with the literature value.
Evaluate the procedure and materials, identifying weaknesses and limitations and state
how they have affected your result.
Suggest any improvements to avoid the errors and others that you have listed.
Aim To determine the empirical formula of copper sulphate.
Requirements
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eye protection
tripod
tongs
gauze
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crucicble + lid
balance,  0.01g
stopwatch
CuSO4.nH2O
Procedure
You will need to start with the hydrated compound and heat it until you have removed all the water and the
compound has become anhydrous.
Safety
The crucible will get very hot so let it cool a little before you handle and transport it.
Data collection and processing (DCP)
Under the heading “Measurements and observations”, design an appropriate results table which contains
all relevant data.
For the processing of the raw data, you will need to use a spreadsheet. You will need to decide on the
necessary calculations and then design a spreadsheet which will do the calculations of your raw data.
You will also need to propagate uncertainties.
IB chemistry internal assessment: formula of copper sulphate
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You will then need to make a printout of the spreadsheet and attach it to your report or insert it in your
document underneath a heading ‘Calculations”.
Evaluation and Conclusion (CE)
Conclusion
Apart from the conclusion based on the experimental results, the experimental result itself should be
compared against an expected value (maybe stated in an hypothesis) or a literature value. In either case,
a % error needs to be calculated where possible.
 If the % error is less than the uncertainty % than no further error analysis is really necessary as the
error can be attributed solely to random error. Random errors are errors which are due to the
limitations or accuracy of the measuring tools used and the taking of readings. Such errors are
predictable (as the manufacturer has stated the accuracy of the equipment) and can therefore be
calculated.
 If the % error is greater than the uncertainty % than further evaluation needs to occur as shown
below
Evaluation of procedure (2nd aspect):
Identification of systematic errors which are errors that can be identified and eliminated. Systematic
errors are due to the quality of the equipment and materials, poor experimental design and ‘incorrect’
use of the equipment. These errors cannot be calculated and are also difficult to evaluate. However,
these systematic errors can be reduced by using better equipment/materials or improved experimental
technique.
Evaluation of procedure consists of:
a. Evaluation of materials/equipment: Measuring tools improperly calibrated? Accurate enough?
Incorrect concentration of reagents? Impure reagents? Amounts of reagents used large enough?
b. Evaluation of method: Are there any flaws in the method which could have caused an error greater
than the % uncertainty? Were some variables not controlled? Were readings duplicated?
In both cases, the limitations (in interpretation of data), weaknesses and errors (=what is wrong with
procedure) of the materials/equipment and method need to be identified.
Evaluation of result
For each identified limitation, weakness or error indicate which data is incorrect, the direction of the error
(more or less)and the impact on the final result.
Improvements
For each suggested weakness, suggest improvements
This can all be done using a table as shown below
Limitation/weakness
Effect on result (=error)
IB chemistry internal assessment: formula of copper sulphate
Improvement
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