How many mL of NaOH are required to reach equivalence point?

Question

Hello all,

I need a little clarification since I figured out 2 ways of doing it and of course 1 way is right.

Vitamin C (L-ascorbic acid; MW = 176.0 g/mol) is a weak acid (pKa = 4.863). Suppose a 500.0 mg tablet is dissolved in water and titrated with 0.100 M NaOH. How many mL of NaOH are required to reach the equivalence point?

Question is, Should I figure the amount of H3O+ concentration and make the mol's of that equal mol's of NaOH to figure out mL? The answer I got for doing it this way is 1.97 mL

OR

Just go ahead and take 500 mg convert it into mols and make those mols = NaOH mols and divide that buy .1 M to get mL? The answer I got doing it this way is 28 mL

Please help me, My test is tm I would love you forever..

Ken McGuire · Accepted Answer

You say you have a test tomorrow, so this answer is too late, I know.

You want the 2nd way.  Really all you need the pKa for is to pick which pH indicator you will use.  If you tried your first way, you will have lots of Vitamin C left, which will partially disassociate again and you are back were you started.

coak · Answer

First, you will be able to desire to verify how many mols of KHP are present day. (0.7414 g KHP)/(204.2 g KHP/mol KHP) = 0.003631 mols KHP on the grounds that KHP reacts one to one with NaOH: (0.003631 mols KHP)(a million mol NaOH/ a million mol KHP) = 0.003631 mols NaOH And now, on the grounds that all of us understand that 0.003631 mols of NaOH have been present day in 22.37 mL of NaOH answer, we are able to verify the molarity (concentration). (0.003631 mols NaOH)/(0.02237 L) = 0.1623 M NaOH *notice that I replaced the mL to L... it quite is by using fact molarity is defined in terms of mols/L -- it is user-friendly to do, purely divide the mL by using one thousand*

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How many mL of NaOH are required to reach equivalence point?

2 Answers