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AS Practical Exam Revision - OCR

I've got a practical exam tomorrow and I'm just in the process of revising for it. Basically, I've done all of the revision for enthalpy and the possible sources of error for evaluation, I was just wondering what sources of error may come up if it's a titration?

So far I've got..

1) Inaccuracies while weighing out a substance (2dp balance might not be enough; in future I could compensate by using a 3dp balance or doing the experiment on a larger scale)
2) Percentage error in equipment (eg. in a measuring cylinder with +/-0.375cm3 error, the (0.375x100)/volume of substance can be done - in future, use a burette..(--what could I say if we're already using a burette?--)
3) An indicator may be too vague in showing the end point, eg. phenolphthalein turns pink at pH8.2, way past neutral. In future, bromothymol blue could be used.

What other things could there be?
And what would be the most significant source of error?

xxxxxx

Reply 1

cowsgomoo

is it definitely a enthalpy experiment? for that i can only think of heat loss to surroundings and etc or evaporation of alcoholic fumes.

as for titration.... maybe you could say its difficult to stop dripping from the burette at the EXACT time colour change as colour change = subjective. maybe.

if you have to dissolve something to make up a solution, say probably all has not dissolved, meaning the concentration calculation might not be accurate

thats it really. help! whats the ocr practical on!

Reply 2

selurnomis

thanks! urm we've been given really strong hints it's an enthalpy one but i'm revising titration as well just in case. :smile:

nobody's really sure though i dont think..

Reply 3

cowsgomoo

i finally udnerstand titration calculations.

ill take your word for it on the enthalpy change doodah. thanks. just need to find some old experiments!

Reply 4

brokenwing216

i think its gunna be titration because it has to relate to the planning and that had titration on it. it also had weight loss on but that was last yrs. so titration me finks.