Chemical Measurements Flashcards

All 8 cards in this deck

Why is there always some uncertainty in a measurement?

Every measuring instrument and every reading has limited precision, so the true value is never known exactly.

What is the range of a set of repeat measurements?

The difference between the largest and smallest value.

How is the range of repeat measurements used as a measure of uncertainty?

The uncertainty is quoted as $\pm$ half the range about the mean.

What are the steps to find the mean and uncertainty of repeat measurements?

e.g. $37.6$, $37.2$, $37.8$, $37.4\,^\circ$C

1. Add the values and divide by how many: mean $= 37.5\,^\circ$C.
2. Range $= 37.8 - 37.2 = 0.6\,^\circ$C.
3. Uncertainty $= \pm$ half the range: $37.5 \pm 0.3\,^\circ$C

What does the $\pm 0.3\,^\circ$C mean in a result written as $16.5 \pm 0.3\,^\circ$C?

It is the uncertainty — the values lie up to $0.3\,^\circ$C either side of the mean.

What is an anomalous result?

A result that does not fit the pattern of the others and is much larger or smaller than expected.

True or false? Anomalous results should be included when calculating the mean.

False. Anomalous results should be identified and excluded before calculating the mean.

True or false? A smaller range in a set of repeat measurements means a smaller uncertainty.

True. The results are closer together, so the uncertainty about the mean is smaller.