# NAME: Chemistry 232 Analytical Chemistry

## Analytical Chemistry

Constants you may need : c=2.998x10

8 m/s, h = 6.626x10

-34 Js

1A. (5 points) What is the frequency associated with green light that has a wavelength of 400 nm?

B. (5 points)What is the energy of this light?

2. (10 points) A substance has an , of 375 M -1 cm -1 . I known my spectrometer is most accurate between 0.4 and 0.9 absorbance units. If I am using a 1 cm pathlength cell, what range of concentrations can I measure most accurately on my spectrophotometer?

3. (10 points)I have a solution that is .1M NaOH, .05M NaCl, .03M K

2

SO

4

. What is the ionic strength of this solution?

4. (15 points) I have a solution with an ionic strength of 0.04. What is the solubility of

BaF

2

in this solution? (K sp

BaF

2

is 1.6x10

-6

, " (Ba) = 500pm " (F) = 350pm) Use the extended Debye-Hückel equation: log

.

51

2 z u u

1

### +

305

2

5. I have 250 mL of .05M HCN.

A. (3 points) What is the p[CN ] of this solution?

B. (4 points) I would like to remove the cyanide before I pour this solution down the drain. Since the K sp

of AgCN is 2.2x10

CN

-

with Ag

+

. How much .035 M AgNO

3

-16

I think I can do this by precipitating the

do I need to add to be equivalent to the CN

-

in my solution?

C. (3 points) What is the p[CN ] after this addition?

6. (10 points) When ammonium acetate dissolves, both the anion and the cation have acid-base properties as seen in the following equilibria:

(NH

4

)

2

SO

4

(s) W 2NH

4

+ + SO

4

2K sp

= 276

NH

4

+ W

NH

3

+ H

+

K a

=5.7x10

-10

SO

4

2 + H

2

O W HSO

4

+ OH . K b

= 9.8x10

-13

Write a charge balance equation for this system.

Write a mass balance equation for this system.

3

4

7(15 points) (A). A 0.1 M solution of an acid has a pH of 1, is this a strong or weak acid.

If it is a weak acid, what is its pK a

?

(B) A 0.1M solution of an acid has a pH of 2, is this a strong or weak acid? If it is a weak acid, what is its pK a

8.(10 points) In our experiment to determine the pK a

of methyl red I wanted a solution that was well buffered around pH 3.0, the pK a

of the indicator. I chose acetic acid (pK a

= 4.757) Other acids I might have tried are: 2-aminobenzoic acid (pK a

2.08) or citric acid (pK a

3.13).

A. Given these choices, what is the best acid for this buffer?

B. Given a .1M solution of this acid and a 0.1M solution of its conjugate base, how would I make up a .1M buffer solution at pH 3. (How many mLs of acid and conjugate base solution would I use?)

9. (10 points) If I have a 0.35 M solution of a weak base that is 94% in the free base form (B) and 6% in the charged form (BH), what is the K b

of the base?