Please Help! Thank you!
A chemistry student weighs out 0.221g of citric acid H3C6H5O7 , a triprotic acid, into a 250ml volumetric flask and dilutes to the mark with distilled water. He plans to titrate the acid with 0.1700M NaOH solution.

Calculate the volume of solution the student will need to add to reach the final equivalence point.

Question

Please Help! Thank you!
A chemistry student weighs out 0.221g of citric acid H3C6H5O7 , a triprotic acid, into a 250ml volumetric flask and dilutes to the mark with distilled water. He plans to titrate the acid with  0.1700M NaOH solution.

Calculate the volume of  solution the student will need to add to reach the final equivalence point.

surry99 · Answer

Hint: what two quantities are the equal at the equivalence point?

anonymous · Answer

I understand that there are 0.001 moles of citric acid and that the formula MV=MV assuming the moles are constant, but I dont understand how to find the final volume when its a triprotic acid

surry99 · Answer

ok, but what does the formula really mean...what two things are you equating?
Once you know that, you can solve the problem.

anonymous · Answer

I don't know, I'm trying to learn it

surry99 · Answer

ok no problem...
at the equivalnce point..
the number of moles of protons from the acid = the number of moles of hydroxide from the base

surry99 · Answer

for every one mole of citric acid , how many moles of protons does it have?

anonymous · Answer

theres 8 H cations so would that be 8?

surry99 · Answer

no, you have to be very careful...just because a molecule has a hydrogen it does not mean that hydrogen will be given up as a proton.  The answer is 3...it is triprotic according to the question

surry99 · Answer

Can you now calculate how many moles are protons are released when you dissolve .221 g of citric acid?

anonymous · Answer

For every one mole of citric acid there is 3 protons

anonymous · Answer

so 0.003?

surry99 · Answer

good...
Now for every one mole of NaOH , how many moles of hydroxide are produced?

anonymous · Answer

1 mole of hydroxide

surry99 · Answer

ok so at EP...
number of moles of protons = number of moles of hydroxide
                          .003           = MbVb(1)         
                         
(the 1 is there to remind you that for every moles of NaOH you get 1 mole of hydroxide)

Now you know Mb from the problem and can solve for Vb, the volume of base required to get to the equivalence point.

It is important to see we are assuming that we are titrating the entire 250 ml of the acid solution.

surry99 · Answer

gotta run now but let me know if you have any questions?

anonymous · Answer

okay thank you

surry99 · Answer

you are very welcome and dont hesitate to conatct me @surry99