Uncertainties in Lab Work

It may be holiday time in the Northern hemisphere but that doesn’t say things go quiet in the world of blogging. If you are a student who is about to start on your IB Chemistry course, or, if you are a student who has yet to do their IA this post is for you! When recording measurements or data in lab work it is vital that you record things correctly, especially in your IA (that’s internal assessment to all you new ...

Data Collection and Processing, Aspect 3

By Thursday, November 4, 2010 , , , , 0

DCP, aspect 3: Students seem to find this difficult to achieve a 'c'. The aspect is looking for students to correctly present their final answer (to the correct number of significant figures) and to display an uncertainty / error value (to the correct number of significant figures). We will consider each part separately: Firstly, the correct number of significant figures. The student should look back through all the data used in DCP aspect 1. The final answer should have the same number of ...

Accurate or Precise? What’s the Difference?

In IA assessment we usually get bogged down with errors and uncertainties. There are, however, more subtle concepts at large! Most students muddle up the words and ideas behind the terms 'accurate' and 'precise'.   In order to understand these concepts it is important that you imagine that the 'thing' you are measuring has a 'true value' and accuracy and precision are measured with respect to this 'true' value. An accurate measurement will give a result nearer to the true value. It is ...

Significant figures

It is important that we express the correct number of significant figures in our calculations. Take the example below. Work through this sample calculation and post your answer: In an experiment to determine the specific heat capacity of an oil, the hydrocarbon was: Heated with an appliance rated 143W ± 1W (P) The heater supplied energy for 634s ± 1s to the oil (t) The initial temperature was 25.5 oC ± 0.5 oC and the final temperature was 47.5 o C ± 0.5 oC ...