General Chemistry Normality Question

[BrownieDDD]

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How many moles of CaCl2 are needed to titrate a 1L, 1 M sol'n of H3PO4 if titrated w/ CaCl2?

a. 0.5 N
b. 1.0 N
c. 1.5 N
d. 2.0 N

answer: C 1.5 N
why: H3PO4 possess three protons per molecule of acid so one and a half molecules of CaCl2 are needed to react with each mole of acid.

I don't really understand how to get the answer. I came up w/ this after reading the solution to try to figure out how to solve it:

NV=NV
nMV=nMV acid on left, Cacl2 on right
3(1)1=2(mol/1)1
3/2= mol

Can someone explain to me how to understand and solve this problem?

 

[deleted397286]

It's one L of solution, so 1 M H3PO4 = one mole of H3PO4

One mole of H3PO4 has 3 moles of H in it. (Ex: "book book book" is three words, but there are 6 O's)

For every mole of H, you need a mole of Cl to neutralize the acid.

CaCl2 has 2 Cl in it... so you would need 1.5 molecules of CaCl2 to neutralize 3 H's.