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Titration Question, I'm Really Really Last Minute Stuck!!! I Know, how juicy

Ok, so you're doing an enthalpy of neutralisation test.

and all's well

you got your graph, worked out q=mc T

But then the mark scheme says "scales up to molar quantities"

and you're thinking wtf?!?!

in the mark scheme it says e.g. x40 for 25cm3 , but I dont know what they mean by this


anyone help a dumb lil chemist? :redface:
Reply 1
Avatar for Funny Mann
Funny Mann
Molar quantity is another way of saying molar concentration. However without the question it is difficult to say where the 40 comes from. Could you possibly post the question?
Reply 2
Avatar for booraad
booraad
14
Enthalpy of Neutralisation question: Monoprotic acid reacting with NaOH

the scale of working used
sensible volume of HA solution ( 20 cm3 to 100 cm3)
sensible volume of NaOH solution ( same or slight excess )
appreciates need for significant ΔT ( at least 5 deg )
appropriate concentration of HA solution ( at least M )

"To score last two points need a definite correct link between conc and ΔT"

... what's the link?
This is the question

When a monobasic acid, HA, in aqueous solution is neutralised by a solution of sodium hydroxide,
the following exothermic reaction occurs.

HA(aq) + NaOH(aq) → NaA(aq) + H2O(l)

When equal volumes of a 0.2 mol dm–3 solution of HA and a 0.2 mol dm–3 solution of sodium hydroxide react together, the temperature rises by about 1°C.

3. A clear explanation, including a sketch graph of temperature against time, showing how you would use your results to calculate, in kJ mol–1, the enthalpy change of neutralisation of the unknown acid, HA.

:confused: :s-smilie:
Reply 4
Avatar for Excalibur
Excalibur
15
I think what they mean is that after you work out your ∆H you should divide that by the moles of acid.
Excalibur
I think what they mean is that after you work out your ∆H you should divide that by the moles of acid.


hmmm maybe but in the mark scheme it says e.g. x40 for 25cm3
Reply 6
Avatar for booraad
booraad
14
bubble_gum_pop
Ok, so you're doing an enthalpy of neutralisation test.

and all's well

you got your graph, worked out q=mc T

But then the mark scheme says "scales up to molar quantities"

and you're thinking wtf?!?!

in the mark scheme it says e.g. x40 for 25cm3 , but I dont know what they mean by this


anyone help a dumb lil chemist? :redface:


I have absolutely no idea why. I can see that 40 * 25cm3 = 1000 cm3 i.e. 1 dm3

Thus you'd have 1M of whatever the solution is, which is useful apparently if that's the concentration you chose to use.
booraad
I have absolutely no idea why. I can see that 40 * 25cm3 = 1000 cm3 i.e. 1 dm3

Thus you'd have 1M of whatever the solution is, which is useful apparently if that's the concentration you chose to use.


oooohhhhhh....c uve answered ur own question

thanks a million...my exams in an hour! :smile:
Reply 8
Avatar for booraad
booraad
14
Hi... I have no idea WHY it's useful to scale up.. but if that's what they want.

I have the exam this afternoon!

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