Assessed Practical (Skill P)

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George Noble 12JK

AS – Assessed Practical (Skill P)

The aim of this experiment is to find out which reaction is correct for the thermal decomposition of copper carbonate out of the following two equations.

2CuCO3(s) ➔ Cu2O(s) + 2CO2(g) + ½O2(g)

CuCO3(s) ➔ CuO(s) + CO2(g)

Avagadro’s constant states that one mole of gas under standard conditions will fill 24dm3 under standard conditions so it is possible to find the amount of gas evolved by measuring the volume. From this it is also possible to find which version of the reaction has taken place.

How much copper carbonate should be used?

The first equation will produce more gas so that is the maximum amount to be taken into account when deciding how much copper carbonate needs to be used. If one mole of copper carbonate is used then one mole of CO2 and 0.25 moles of O2 will be evolved. This will occupy 30dm3 in total. One mole of copper carbonate has a mass of 123.664g.

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Because most gas syringes are 100cm3 the amount of gas evolved needs to be less than this. To make the experiment such that 60cm3 will be evolved the mass of copper carbonate needs to be divided by 500. Having 60cm3 gas evolved will leave room in the gas syringe in case the conditions are not perfect for the experiment. If the volume was calculated so that 90cm3 gas would be evolved there is a chance that the gas syringe would not be able to take it.

30000/500 = 60

123.664/500 = 0.247

Therefore the amount of copper carbonate that ...

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Spelling, grammar, and punctuation are all done to a good standard. The layout of the text is also done well with clear subheadings and laid out calculations.

The introduction is good, the equations used are correct. The candidate does not explain clearly why Avagadros constant means that we will know which substance is made which should have been explained a bit clearer. The theory behind the experiment is explained well, but the calculations and thinking behind their statements should be labelled more clearly as they tend to jump with assumptions that the person reading understand where they have for example got the 30 decimetres from with the first equation. The gas syringe part is also not explained clearly. The conditions for the experiment are explained well. The results and calculations are not finished, but to their stage they are correct.

The response to the question was done well, but the candidate had a tendency to favour one equation over the other in examining the moles of gas produced, and explained this without explaining the theory behind the other one most of the time, so the candidate should revise their work to give a balanced view. The piece of work needs finishing.