Question

1) Which of the following aqueous solutions are good buffer systems?
.

a. 0.29 M hydroiodic acid + 0.20 M sodium iodide .

b. 0.12 M barium hydroxide + 0.29 M barium chloride .

c. 0.14 M nitrous acid + 0.12 M potassium nitrite .

d. 0.34 M ammonium nitrate + 0.36 M ammonia .

e. 0.31 M hydrofluoric acid + 0.29 M potassium fluoride .

2)A solution contains 0.486 M NH₄I and 0.480 M ammonia.

The pH of this solution is .

3)

An aqueous solution contains 0.26 M ammonium nitrate.

One Liter of this solution could be converted into a buffer by the addition of:

(Assume that the volume remains constant as each substance is added.) Select one or more of the following

(A) 0.13 mol HI

(B)  0.064 mol Ba(OH)₂

(C) 0.26 mol HI

(D)  0.25 mol Ba(NO₃)₂

( E) 0.25 mol NH₃

₄₎

How many grams of solid potassium cyanide should be added to 0.500 L of a 0.188 M hydrocyanic acid solution to prepare a buffer with a pH of 10.000?

grams potassium cyanide =  g

5) How many moles of sodium hydroxide would have to be added to 125 mL of a 0.371 M hydrofluoric acid solution, in order to prepare a buffer with a pH of 3.410?

Answer 1

1)

Which of the following aqueous solutions are good buffer systems

Answer :

c. 0.14 M nitrous acid + 0.12 M potassium nitrite .

d. 0.34 M ammonium nitrate + 0.36 M ammonia .

e. 0.31 M hydrofluoric acid + 0.29 M potassium fluoride .

2)

A solution contains 0.486 M NH₄I and 0.480 M ammonia.

pH = pKa + log [conjugate base / acid]

     = 9.26 + log [0.480 / 0.486]

pH = 9.255

3)

An aqueous solution contains 0.26 M ammonium nitrate.

Answer :

(B)  0.064 mol Ba(OH)₂

( E) 0.25 mol NH₃

Buffer is formed by the combination of weak acid and its conjugate base or weak base and its conjugate acid.