Question

solution is 0.0000290 M NaF
a) What mass of NaF is dissolved in 1.00 L of solution?
b) Express this concentration in ppm.

Answer 1

Explanation:

1. Calculate the pH of a solution that is 0.25 M HF and 0.10 M NaF. Also, predict if these

concentrations are appropriate to make a buffer solution. (5 pts)

Ka = 3.5 x 10-4

HF ⇄ H

+

+ F-

Henderson-Hasselbalch Equation

= +

[

−]

[]

= − log(3.4 10

−4

) +

(0.10)

(0.25)

= 3.46 − 0.40 = .

Buffer Range

2.46 – 4.46

This solution is within the buffer range, thus the concentrations are appropriate to make a buffer

solution.

2. Calculate the pH of a buffer solution that is 0.20 M in HCN and 0.12 M in NaCN. Will the pH

change if the solution is diluted by a factor of 2? Explain to receive full credit. (5 pts)

Ka = 4.9 x 10-10

HCN ⇄ H

+ + CN-

Henderson-Hasselbalch Equation

= +

[

−]

[]

= − log(4.9 10

−10) +

(0.12)

(0.20)

= 9.31 − 0.22 = .

Dilution will not change the pH because the ratio of the conjugate base to acid will remain the

same.

[

−]/2

[]/2

=

[

−]

[]