# A level chemistry - uncertainty

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#1
What is the formula for it? I keep getting conflicitng info

Please could you give me an example of when it is applied please? Thank you
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1 month ago
#2
(Original post by aroundanaxis)
What is the formula for it? I keep getting conflicitng info

Please could you give me an example of when it is applied please? Thank you
As in percentage error?
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#3
(Original post by Jaegis)
As in percentage error?
i mean that's part of it yeah. Just anything u can tell me rly. THnks
0
1 month ago
#4
https://pmt.physicsandmathstutor.com...ertainties.pdf

Have a read through this. Anything you don’t understand specifically, come back and ask for clarification.
Last edited by GabiAbi84; 1 month ago
2
1 month ago
#5
(Original post by aroundanaxis)
i mean that's part of it yeah. Just anything u can tell me rly. THnks
The less accurate your equipment (like a glass pipette or a mass balance), the more uncertain your results are. If your scales say that the mass of a beaker is, I don't know, 21g, it could really be something like 21.4g or 20.5g (I'm not the best at rounding sig. figs., so don't quote me on that), which means you don't know the precise result - there's an uncertainty. Over a whole experiment, every piece of equipment you use will have some uncertainty in the result, so by the end there is a larger overall uncertainty. The uncertainty can be calculated as a percentage, both for an individual measurement and all of them together in an experiment;

Percentage error = total uncertainty / reading x 100

So if you took a reading of 25cm3 from a burette, which has an uncertainty of 0.5cm3, you'd get

0.5 / 25 x 100 = 2% percentage error

I might be remembering the burette's uncertainty wrong, but you get the idea.
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#6
So is uncertainty half an interval?

Eg if its a 10cm3 measuring cylinder, the uncertainty is +/- 0.5cm3?
0
1 month ago
#7
(Original post by aroundanaxis)
So is uncertainty half an interval?

Eg if its a 10cm3 measuring cylinder, the uncertainty is +/- 0.5cm3?
Well, I was actually wrong about the exact uncertainty - for that burette it's actually 0.05. But often, yes. Think about it - when you're doing a titration, you can tell if the acid is on the mm mark or between two of them, but you can't accurately tell anything more than that. So you give either a .00 or a .05. That's not the case for everything, though, so be careful.
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1 month ago
#8
(Original post by Jaegis)
The less accurate your equipment (like a glass pipette or a mass balance), the more uncertain your results are. If your scales say that the mass of a beaker is, I don't know, 21g, it could really be something like 21.4g or 20.5g (I'm not the best at rounding sig. figs., so don't quote me on that), which means you don't know the precise result - there's an uncertainty. Over a whole experiment, every piece of equipment you use will have some uncertainty in the result, so by the end there is a larger overall uncertainty. The uncertainty can be calculated as a percentage, both for an individual measurement and all of them together in an experiment;

Percentage error = total uncertainty / reading x 100

So if you took a reading of 25cm3 from a burette, which has an uncertainty of 0.5cm3, you'd get

0.5 / 25 x 100 = 2% percentage error

I might be remembering the burette's uncertainty wrong, but you get the idea.
if working out percentage uncertainty of a burette from a titration experiment specifically, 0.05cm3 should be doubled to 0.1cm3 because the burette is read twice in the experiment (initial reading and final reading) therefore the total uncertainty part of the formula
Percentage error = total uncertainty / reading x 100
would be 0.1
1
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