Percentage error???Grrr

Ah, i hate % error! Is there a difference between precisions error and % error? I've got that the precision error for a litre volumeteric flask is 0.8 but that for a 250cm^3 flask its 0.3...is this right? How does it work?

Reply 1

emancipazione

I'm pretty much sure they're the same thing :smile:

To calculate percentage error, all you've gotta do is:

(accuracy of equipment ÷ final measurement) x 100

you can use this to check whether the given precision errors are correct. If your teacher gave you them, and you're using them for coursework, you can just say that they're standard precision errors given by a reliable authorative figure - a friend of mine got through with saying that no bother :biggrin:

Reply 2

b33jal

GAH im not alone! i hate it too, i dont get what the accuracy of the equipment is.. :s-smilie:

Reply 3

charco

Study Forum Helper

it's usually written on measuring apparatus - eg volumetric flask 250ml +/- 0.23
pipette 25ml +/0.4
etc
If it's electronic measuring apparatus take the first decimal place that CANT be seen as +/- 5
eg for a gram 2dp electronic balance the tolerance is +/-0.005g

Reply 4

SparxXx

so is the percentage error for electronic balance +/- 0.005? or +/-5?

Reply 5

EierVonSatan

SparxXx

so is the percentage error for electronic balance +/- 0.005? or +/-5?

For a balance that measures 2 decimal places its +/- 0.005
for 3dp its +/- 0.0005
for 4dp its +/- 0.00005
and so on...

this is absolute error not percentage error :smile:

Reply 6

Rubs

One question - how would you know the error of values that are given to you? e.g. pH/activity coefficients to 2d.p., or other values given to 1/2 s.f. (no d.p.)? I was thinking the first one would be ±0.01 and the latter ±0.5.