The theme for the next couple of days will be Conclusion and Evaluation (CEv).
Aspect one is split into three parts and is, in my opinion, the hardest of all of the aspect to achieve a ‘c’ in.
Firstly, the student needs to write a good IB level conclusion – what do the results actually mean. There is no longer a ‘hypothesis’ to write, so this is the part of IA that is really testing an understanding of chemical knowledge.
Secondly, the student needs to compare the calculated value (from DCP aspect 3) with a data book / literature value. If there is no value, the student needs to make this clear!
Finally, the student should comment on whether the systematic error or random error is bigger.
If the calculated value is 265 + / – 30 and the literature value is 260, then we have a pretty good experiment, as the calculated value lies within the error margins of the literature value. This will mean that the systematic errors are small.
However, if the calculated value was 895 + / 30, the experiment would not be so good. The literature value is outside the error margins of the calculated value. In this lab, the systematic errors are large.
Systematic errors are errors that cannot be directly measured – a classic example of this is heat loss in an enthalpy of combustion lab.
The student should also mention the significance of the direction of the calculated value compared to the literature value. Again, in enthalpy of combustion labs, a calculated value will always be less negative than the actual value – for example, a calculated value may be – 300 kJ mol -1 but the actual value is – 800 kJ mol -1. The calculated value is closer to zero than the literature value.
The student would expected to explain this phenonema – ie, heat has been lost to the air and has not gone into heating the calorimeter, hence the calorimeter has recorded less energy evolved by the fuel.
Tomorrow, CEV, aspect 2