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titrations

In titrations (redox titrations), when we take a sample ((aliquot) like 25 cm3 of 250) of the original solution does the concentration change or remain the same???? Ik the moles change due to the change of volume only.. But yeah I'm not very sure :frown: Can someone explain whats going on
(edited 7 years ago)
Reply 1
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MAS98
8
The concentration remains the same (theoretically).

The volume, as you know, changes but so does the mole value. Thus, when you divide these together, you'd virtually get the same concentration as the one from the original solution.
Reply 2
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MAS98
8
Its like having twenty apples and ten baskets. If i distribute them equally, each basket would have two apples. (just like concentration)

So if you pick a sample of, say, two baskets, you'd get four apples.

But the "concentration" is still the same as you still have two apples in each basket.
Original post by MAS98
The concentration remains the same (theoretically).

The volume, as you know, changes but so does the mole value. Thus, when you divide these together, you'd virtually get the same concentration as the one from the original solution.


yup so thats actually what I had understood till I saw this question :frown:
in q 21)iv) it says calculate the difference between the initial and final concentrations, aren't they the samee ugh

the q is from IAL 2015 June, I've attached it below
here is it
Capture.PNG38.3KB
2.PNG16.7KB
sorry forgot to attach part ii)
3.PNG17.6KB
someone please helpppp x
Reply 7
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MAS98
8
Hi sorry for the wait. Was a bit busy. But from my understanding it wants the difference between the conc of the solution used to SOAK the skin and R.

If you look at the paragraphs before the first question, I guess the initial concentration is the one given with 226.8g and 45dm3. So you have to essentially calculate the initial concentration (in mol/dm3) by using the Mr.

Then once you get that, you'd need to use the concentration of R that you calculated in the question before to find the difference.
Reply 8
Avatar for MAS98
MAS98
8
To put it into perspective, if you're also asking why they're both different concentrations,

Initially, you had a fixed intitial concentration of KOH.

Then the solution was used to soak the animal skin, so some of the KOH took part in a reaction to form, say, A.

The remaining KOH particles (or the residue) is now inside a solution with A (sharing the total volume). So the concentration with respect to KOH decreases.

Well at least thats how i see it. Sorry my chemistry is a bit rusty as I graduated from A-Levels last year but i hope you understand! If you have any questions let me know I'll be glad to help.
Thanks sooo much! :tongue:

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