titration curves Watch

Da Mouse
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#1
Report Thread starter 12 years ago
#1
hiya guys. i'm not sure if this is a trick question or not. I've been asked:-
how many cm3 of the base (0.1moldm-3 of NaOH) would you expect to add to 25cm3 of the acid (0.1 moldm-3 H3PO3) before the first rapid rise.

First of all i thought 25cm3 but then for evey H3PO3 there's 3H atoms and i dont know if H3PO3 fully dissociates into 3H and PO3 so it might be 75cm3

also, i've also been asked, why, on addition of base to the acid can the pH of the resultant system never reach that of 0.1moldm-3 NaOH.
is it because that there is always acid to netralise it?
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JayEm
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Report 12 years ago
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You'd get 3 equivalence points. I'm guessing the first would be on adding about 25cm3, the second at approx. 50cm3 and the third at approx. 75cm3.

You never get 0.1M NaOH because water formed through neutralisation dilutes the base.
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Borek
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#3
Report 12 years ago
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Two visible endpoints only, third proton is too weak. Check out pH calculator - trial version will draw titration curve for phosphoric acid.
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