Help explain GC Destroyer #193

[helpme123]

30.0 mL of 0.20 M Ba(OH)2 is required to neutralize 25 mL of citric acid (H3C6H5O7). What is the molarity of the citric acid?

I understand to do N1V1=N2V2 and double the concentration of Ba(OH)2. But after all that they tell me that I have to divide by 3 because there are 3 ionizeable protons on citric acid. Why do we have to divide by 3?

I remember a similar question (#128): 20 mL of 0.012 M Ca(OH)2 is added to 48 mL of HBr, what is the concentration of HBr?

Do you have to divide by 1 in this case, which ends up being the answer if you weren't to divide it anyways? So, my question is do you always divide by the # of ionizeable protons in these types of questions?

Thanks!

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[read001]

Use nM1V1 = nM2V2..... n is number of mole of (OH) or (H+). M is morality and V is volume.
so (2)(.20)(30) = (3)(M2)(25) solve for M2....

 

[helpme123]

Thanks! That really simplifies both formulas down for me.

 

[stevepearls]

That's good information, please keep it up and also provide more detailed information here.

 

[thebigrisky]

This is always a question type I make dumb errors on. Relatively new to the chem questions. Why do you assign 2 to Ba(OH)2 and a 3 to the (H3C6H5O7)? Are you taking the M of each and going through the M.W. of each to get at the number of moles or are you getting the 2 and 3 from the number of ions each on breaks into? If so, how would you know H3C6H5O7 breaks into three ions? Or is it understood that since it has H's, C's and O's that it would be 3 ion types.