Question

Exercise 1: Consider the following information for a series of solutions of weak acids, HA: Weak acid PK, К. If [HA], is... then [H3O+]E ... and pH HCOOH 3.74 1.8 x 10-4 0.100 M 4.2 x 10² M 2.38 HNO2 3.37 4.2 x 10-4 0.100 M 6.3 x 10-M 2.20 HCN 9.20 6.3 x 10-10 0.100 M 7.9 x 10ⓇM 5.10 4.23 0.100 M 5.9 10-M HOCI 7.46 3.5 x 10-8 0.200 M 8.3 x 10M 4.07 0.400 M 1.2 x 10+M | 3.93 Use the data provided to qualitatively outline the relationships between (a) ... initial acid concentration [HA], and pH (b) ...Ka pKa, acid strength, [H3O+]e and pH

Answer 1

аас Белсіре 1 a) from the information in the table it can be seen that for a particular aud CHOCl in this case) with inerease in initial acid concentration [HA], the pH decreases This is because more higher initial concentration of acid means higher [H3O'J and pH = -log[120+] will be lower. For different acids relation between [lt A Jo and pH can not be detey mined as Ka iš different for every one. b) From the table it is seen that higher Ka - lower pka (pha= -log Ka) → higher [430 higher acidity a lower pH (pH = -log[(120) pH lower means the acid have higher and strength. Exercise 2 a) pol=14- H pOH = -log[ot ] opk6= log ko Kb = base dissociation constant.(the equilibrium constant for B Ko zł Bt] [ok] so ko higher means higher [ot ] [BOH] So the relation will be similar as that of acids but the pH will have opposite Strength (as pH = 14 -poh) a higher Kb lower pkb higher [ok] - lower pon - higher pH higher base shength: b) So, the relation between pho and pH is lower the pko , higher is pH. The pH of equimolar aqueous so) ulions of the bases is compared' as follows, Smallest pho / CH₂ NH₂ NH3 HONHz GHs NH₃ / hargest pKb highest pH - I lowest pH pH decreases. Exercise 3 a) Ka and Kip are related for a conjugate acid base pair. HA --A®+H* BOH -> 6+ +010 acid in conjugate lase base its conjugate acid.

For conjugate acid base pair, the acid dissociation constant ka and the base disociation constant Ko are related as following, Kalkp = kw Kw is the autoionization constant b) higher audity of acid, lower the basicity of its conjugate base arranging the acids in exercise 1 from lowest to highest acid strength. we get, Acids: HON Hoc HCOOH HNO2 higher acidity corresponding conjugate :- 0 0 Heol Noz base ✓ lower basicity > Weakest base. base Strongest base 2) higher the basicity of base, lower the auidity of conjugate acidl. base! CH₂ N ₂ NH₂ HONHz Cotts Nitz busicily decreases conjugate acid city with Nika Holtz CG HSWlz > Strongest Spongest audily increases : I auidity increases. wennent Weakest aud