Question

xc. Predict semi-quantitatively whether the following solutions are acidic, basic, or nearly neutral. (a) NH4NO2 (b) NH4F (c) NH4CN (d) NaHCO (e) K2HPO4 (f) (NHA)2SO The first part is solved below. Use similar reasoning to make predictions for the other solutions (a) Ka for NH,-5.6x 1010 and Ko for NO is 2.2x 10. Since the Ka is about 25 times larger than Kb, the solution should be acidic.

Answer 1

a. NH₄NO₂ is a salt that comes from a weak acid (NH₄⁺) and a weak base (NO₂^-) so that, the pH depends of the ionization constants.

K_a (NH₄⁺)= 5.6 x 10^-10

K_b (NO₂^-)= 2.2x 10^-11

K_a > K_b so, that solution is acidic.

b. NH₄F is a salt that comes from a weak acid (NH₄⁺) and a weak base (F^-) so that, the pH depends of the ionization constants.

K_a (NH₄⁺)= 5.6 x 10^-10

K_b (F^-)= 2.9x 10^-11

K_a > K_b so, that solution is acidic.

c.NH₄CN is a salt that comes from a weak acid (NH₄⁺) and a weak base (CN^-) so that, the pH depends of the ionization constants.

K_a (NH₄⁺)= 5.6 x 10^-10

K_b (CN^-)= 2.0x 10^-5

K_a < K_b so, that solution is basic.

d. NaHCO₃ is a salt that comes from a weak acid (Na⁺) and a weak base (HCO₃^-) so that, the pH depends of the ionization constants.

Na⁺ is a conjugate acid of a very strong base (NaOH) so that, K_a is very small.

K_b (HCO₃^-)= 2.3 x 10^-8

K_a << K_b so, that solution is basic.

e.K₂HPO₄ is a salt that comes from a weak acid (K⁺) and a weak base (HPO₄^-2) so that, the pH depends of the ionization constants.

K⁺ is a conjugate acid of a very strong base (KOH) so that, K_a is very small.

K_b (HPO₄^-2)= 1.6 x 10^-7

K_a << K_b so, that solution is basic.

f. (NH₄)₂SO₄ is a salt that comes from a weak acid (NH₄⁺) and a weak base (SO₄^-2) so that, the pH depends of the ionization constants.

K_a (NH₄⁺)= 5.6 x 10^-10

K_b (SO₄^-2)= 8.33x 10^-13

K_a > K_b so, that solution is acidic.