20.000 mL aliquots of a phosphoric acid solution with an unknown concentration is titrated with some 0.624 mol/L sodium hydroxide solution.The average volume of the sodium hydroxide added was 24.01 mL. What is the concentration of the phosphoric acid?

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Answer 1 · 2017-05-31T20:17:57

#[H_3PO_4]=0.375*mol*L^-1#.

We assess the reaction............

#H_3PO_4(aq) + 2NaOH(aq) rarr Na_2HPO_4(aq) + 2H_2O(l)#

Note that the phosphoric acid is A DIACID not a triacid in aqueous solution, and we use this stoichiometry accordingly.

#"Concentration of acid"=(0.624*mol*L^-1xx24.01xx10^-3*L)/(2xx20.00xx10^-3*L)#

#=0.375*mol*L^-1#