Chemistry - A Molecular Science

Chapter 12 Acid-Base Chemistry

e) Solutions of ammonium nitrate and sodium bromide are mixed.

(^1) NH
1+ 4

• NO
  1- 3


• Na
  1+ + Br
  1-^
  2

1. No precipitate is predicted. NH

1+ 4

ion is a weak acid, but Br

1- ion is a weaker base

than water,* so NH

1+ 4

would react with water, not bromide ion in aqueous solution.

Thus, the only reaction to take place would be the following:

NH

1+ 4

+ H

O 2

U

NH

+ OH 3

1-^

2.

NaNO

is soluble, so Na 3

1+ and NO

1- 3

are spectator ions.

f) Hydrogen sulfide is added to an excess of aqueous NH

. 3

This is a weak acid/weak base reaction. H

S is a diprotic acid (having two protons); but, in 2

Brønsted acid-base reactions, the prot

ons are removed one at a time. H

S is a stronger 2

acid than NH

1+ 4

, but the equilibrium constant (K = (1.0x10

-7)/(5.6x10

-10

) = 1.8x10

2 ) is not

greater than 10

3 , so double arrows are used.

H NH H

H SH

HN

H

H

H

H S

NH

+ H 3

S 2

U

NH

1+ 4

+ HS

1-^

HS

1- is amphiprotic because it is

not only the conj

ugate base of H

S, but it is also the 2

conjugate acid of the S

2- ion. However, a check of the acid-base table indicates that HS

1-

is such a weak acid that it does not reac

t extensively with the remaining (excess) NH

(K = 3

(1.3x10

-13

)/(5.6x10

-10

) = 2.3x10

-4). HS

1- is the predominant sulfur-containing species.

H NH H

SH

HN

H

H

H

-2S

NH

+ HS 3

1-^

U

NH

1+ 4

+ S

2-^

(^1) Ag
1+ + F
1- + H
O 3
1+ + Cl
1-^
2
g) Solutions of silver fluoride and hydrochloric acid are mixed.
Hydrochloric acid is a strong acid and must be written as H
O 3
1+ + Cl
1-.

1. Silver chloride is insoluble, so it precip

itates from the solution (Solubility Rule 3).

Ag

1+ + Cl

1-^

→

AgCl(s)

2. This is a strong acid-weak base reaction.

H

O 3

1+ + F

1-^

→

HF + H

O K = (1.0)/(7.2x10 2

-4) = 1.4x10

3

Both reactions are extensive.

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State

University