What volume in milliliters of 9.850×10−2 M sodium hydroxide solution is required to reach the equivalence point in the complete titration of a 17.0 mL sample of 0.144 M phosphoric acid?

Answer 1

I have a master equation for all equivalence point problems - it is the following and it is so convenient!

Molarity Acid x Volume Acid x (# of acidic H's) = Molarity Base x Volume Base x (# OH- or basic sites)

So the most confusing part for students is the acid H's and OH-

so for examples: HCl has 1 acidic H, H2SO4 has 2 acidic H's

Ca(OH)2 has 2 OH- - make sense

so now to the problem.

What volume in milliliters of 9.850×10−2 M sodium hydroxide solution is required to reach the equivalence point in the complete titration of a 17.0 mL sample of 0.144 M phosphoric acid?

NaOH is the base: 9.850 x10^-2 M is the MOlarity of the base

Volume of base = we don't know

number of OH- is 1

Molarity of Acid: 0.144 M

Volume of acid: 17.0 mL

Number of acidic H's you need to know phosphoric acid is H3PO4 so 3 acidic H's

Set it up now:

(0.144)(17.0)(3) = (9.850 x 10^-2)(V)(1)

Solve for V = 74.6 mL