# OCR Chemistry AS Evaluative

Here are some useful hints for the OCR AS Evaluative paper.

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• Created by: FrankieO
• Created on: 22-01-15 20:22
Why is it best to repeat measurements and get several results?
To increase the reliability of the data. Anomalous results can also be identified.
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What should be done with these results?
An average should be calculated.
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Are all the results averaged?
Only if there are no anomalous results.
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How do you calculate percentage error?
(uncertainty/measurement) x 100%
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What should happen if there are 2 measurement made to get a value?
Then the uncertainty error will be doubled.
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What is the problem of using small masses or volumes?
The percentage error will be higher.
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Apart from reducing errors, how could you get a more accurate result?
Use a more accurate balance (3 decimal places instead of 2 decimal places). Or use a burette rather than a measuring cylinder.
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When is increasing the accuracy of a mass or a volume not relevant?
When it is in excess.
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How can such heat losses be minimised?
Increase the insulation around the container.
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How should the result be rounded?
The result should contain the same number of significant figures as the measurement that has the smallest number of significant figures. (Remember to always read the question carefully! Some questions specify what to round the answer to.)
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If a measurement is given in cm^3, how is it converted to dm^3?
It is divided by 1000.
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Moles =
concentration x volume
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Moles =
Mass / Mr
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Volume of GAS =
Number of moles x 24
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## Other cards in this set

### Card 2

#### Front

What should be done with these results?

#### Back

An average should be calculated.

### Card 3

#### Front

Are all the results averaged?

### Card 4

#### Front

How do you calculate percentage error?

### Card 5

#### Front

What should happen if there are 2 measurement made to get a value?