Question

(b) You will titrate 25.00mL of Histidine dihydrochloride solution of unknown concentration with the secondary standard NaOH. Use a value of 0.025M Histidine dihydrochloride to estimate the volume of NaOH required to completely deprotonate the histidine dihydrochloride. The concentration of NaOH is .1254 M. This calculated volume is an estimate of the third equivalence point. Use this value to estimate the first and second equivalence point volumes.

(c) Calculate the volumes at ~75% and ~90% of the three approximated equivalence points and record these values in the copied Data Table F from your manual pages.

Data Table F: Calc approximate volumes to reach endpoint

	V(NaOH) at 1st equivalence point	V(NaOH) at second equivalence point	V(NaOH) at third equivalence point
estimated volume
about 90% of the estimated volume
about 75% of the estimated volume

Answer 1

b) M₁V₁ = M₂V₂

0.025 * 25 = 0.1254 * V₂

V₂ = 4.98 mL this volume is the third equivalence point

so total volume required for titration = 4.98 mL

so 1st equivalence point will be 4.98/3 = 1.66 mL

2nd Equivalence point = 1.66*2 = 3.32 mL

c) (VNaOH) at 75 % of 1st approximated equivalence points = 1.66*75/100 = 1.245 mL

(VNaOH) at 90 % of 1st approximated equivalence points = 1.66*90/100 = 1.494 mL

(VNaOH) at 75 % of 2nd approximated equivalence points = 3.32 *75/100 = 2.49 mL

(VNaOH) at 90 % of 2nd approximated equivalence points = 3.32 *90/100 = 2.988 mL

(VNaOH) at 75 % of 3rd approximated equivalence points = 4.98 *75/100 = 3.735 mL

(VNaOH) at 90 % of 3rd approximated equivalence points = 4.98 *90/100 = 4.482 mL