Determine the K for the following species in water. For those species that do no

Question

Determine the K for the following species in water. For those species that do not already have a counter ion, select a neutral counter ion for the salt.

a.) CN-

b.) pryidinium chloride (aka pyridine hydrochloride)

c.) CO32-

d.) methylammonium chloride (aka methylamine hydrochloride)

e.) CH3NH3F

f.) HASO42- (show both as an acid and a base)

g.) H2PO42- (show both as an acid and a base)

answers: a) Kb= 1.6x 10-5 b.) Ka= 6.67x10-6 c.) Kb1= 2.1x10-4   d.) Ka= 2.4x10-11   e.) Koverall= 3.6x10-8   

f.) Ka3= 3.2x10-12 , Kb2= 1x10-7 g.) Ka2= 6.3x10-8 , Kb3= 1.4x10-12

Explanation / Answer

K values for the species

a) CN-

Kb = Kw/Ka = 1 x 10^-14/6.2 x 10^-10 = 1.6 x 10^-5

b) pyridinium chloride

Ka = Kw/Kb = 1 x 10^-14/1.7 x 10^-9 = 6 x 10^-6

c) CO3^2-

Kb = Kw/Ka2 = 1 x 10^-14/4.7 x 10^-11 = 2.1 x 10^-4

d) methylammonium chloride

Ka = Kw/Kb = 1 x 10^-14/4.4 x 10^-4 = 2.3 x 10^-11

e) CH3NH3F

Ka for HF = 6.6 x 10^-4

Ka for CH3NH3+ = 2.3 x 10^-11

Overall K = 2.3 x 10^-11/6.6 x 10^-4 = 3.5 x 10^-8

f) HAsO4^2-

Ka3 = 3.2 x 10^-12

Kb2 = 1 x 10^-14/1.1 x 10^-7 = 1 x 10^-7

g) H2PO4^2-

Ka2 = 6.2 x 10^-8

Kb3 = 1 x 10^-14/7.5 x 10^-3 = 1.3 x 10^-12

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