Which one of these equations represents the reaction of a weak acid with a stron

Question

Which one of these equations represents the reaction of a weak acid with a strong base? OH^-(aq) + HCN(aq) rightarrow H_2O(aq) + CN^- (aq) HCN(aq) + CH_3HN_2(aq) rightarrow CH_3NH_3^+ (aq) + CN^- (aq) H^+ (aq) + CH_2NH_2(aq) rightarrow CH_3NH_3^+ (aq) H^+ (aq) + OH^- (aq) rightarrow H_2O(aq) Which one of the following equations represents the ionization of a weak base in water? NH_3(aq) + H_3O(aq) NH_2^+ (aq) + H_2O(I) NH_3(aq) + H_2O(I) NH_2^+ (aq) + H_2O^+ (aq) NH_3(aq) + OH^- (aq) NH_2^- (aq) + H_2O(I) NH_2(aq) + H_2O(I) NH_4^+ (aq) + OH^- (aq) NH_3(aq) + H_2O(I) NH_4^- (aq) + OH^+ (aq) Calculate the pH of a 1.6 M KOH solution. 0.20 14.20 -0.20 13.80 1.60 Calculate the pH of a 0.021 M NaCN solution. [K_a (HCN) = 4.9 times 10^-10] 10.82 5.49 1.68 3.18 7.00

Explanation / Answer

17)

A) OH-(aq) + HCN(aq) --------> H2O(aq) + CN-(aq)

18)

D) NH3(aq) + H2O(l) <=====> NH4+(aq) + OH-(aq)

19) B

KOH ------> K+ + OH-

[KOH] = [OH-] = 1.6 M

pOH = -log[OH-] = -log(1.6) = -0.20

pH = 14 - pOH = 14 -(-0.20)

pH = 14.20

20) A

pH of a salt of strong base and weak acid can be calculated by following equation,

pH = 7 + 1/2 { pKa + log C }

Ka = 4.9 x 10^-10 => pKa = 9.3

C = [ NaCN ] = 0.021

pH = 7 + 1/2 { 9.3 + log(0.021)}

pH = 10.82

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