Question

In a titration, 25 mL of 0.10 M weak diprotic acid solution was titrated by 0.10 M sodium hydroxide, NaOH, and produced a titration curve listed below. (20 points total) 14,0 3. 12.0 10.0 8.0 pH 6.0 4.0 2.0 10.0 5.0 20.0 30.0 15.0 25.0 Volume of 0.100 M NaOH, mL The acid used in above titration is a weak diprotic acid. Briefly explain how you know it's diprotic from looking at the titration curve and how you know a weak acid. [-3 points each] a. Answers: What is the approximate pHof equivalence point 1? Equivalence point 2? [-2 points each] b. Answer (equivalence point 1): Answer (equivalence point 2): From the curve, estimate the pKat and pKaz [-2 points each) c. Answer(pKa): Answer (pK,1): d. If we used H,C,Oa as the weak diprotic acid, which of the four species, H2C,O, HC,04 CO or OH, will be present in the highest concentrations in a solution at the given pH's below? If you think any of the above are equal, write the two species that are equal as an equivalence (i.e. H,C,O, HC ,O. ). [-6 points total; -2 points each] Answer: pH 12 pH 5 Answer: pH 8 Answer:

Answer 1

@ HA H+ HT HA - HT + 12 A2- 6 HA- H₂A PHAT 2 H₂A vol of base - base - - Henderson eq I nonprotonated pr = pka tlogt 5 protonated e. At eq. point 1 pH = pka] - Eg. point to pH = ~42 point 2 From curre, PH ~ 10

Therefore 6. pray = my 2 10 Pkay = 1.25 H₂ COy - Ht + HCO, -pka, 487 Heront + og 2-3 Ampiaana Nows from Henderson eqr. When pH7 pra Non protonated version dominates- . A pH = 5 Hсу — солі і/ bе more concentrated At pH=8 C2002- will be more concertate At PH = 12 on will be more concentrate due to addition of Nadt)