ACA

Oklahoma State University

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Answer all of the questions below. If you do not know an answer enter CNA. However, it will help me the most if you answer each question with your best intuition/idea about what would be a reasonable answer.


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1. For each of the following combinations indicate whether the mixture is a buffer or not.

a) mixing 20.0 mL of 0.500 M HC2H3O2 and 20.0 mL of 0.500 M NaC2H3O2

is this mixture a buffer? (Yes or No)

b) 500. mL of a solution containing 0.200 M NH3 and 0.250 M NH4NO3

is this mixture a buffer? (Yes or No)

c) mixing 45.0 mL HCl and 35.0 mL NaOH

is this mixture a buffer? (Yes or No)

d) mixing 50.0 mL 0.500 M HC2H3O2 and 25 mL 0.500 M NaOH

is this mixture a buffer? (Yes or No)

2. A buffer solution is prepared by mixing 50.0 mL of 0.350 M HC3H5O2 and 50.0 mL 0.400 M KC3H5O2. Calculate

a) moles of in the HC3H5O2 solution

moles HC3H5O2

b) moles of in the KC3H5O2 solution

moles KC3H5O2

3. Which component of the buffer in Question 2 will react with;

a) HCl?

b) NaOH?

Example calculation:

Buffers neutralize strong acids and strong bases. For example if 0.0045 mol HCl are added to a buffer solution containing 0.0200 mol HC2H3O2 and 0.0300 mol NaC2H3O2 the HCl is neutralized by the NaC2H3O2.

 

H+

+ C2H3O2-

-->

HC2H3O2

 + H2O

Initial

0.00450 mol

0.0300 mol

 

0.0200 mol

 -

Change

-0.00450 mol

-0.00450 mol

 

+0.00450 mol

 -

Ending

0

0.0255 mol

 

0.0245 mol

  

After the neutralization the resulting solution contains a weak acid and its conjugate base, which is a buffer (common ion) solution.

Other possible results after neutralization when adding a strong acid or base to a buffer could be: a salt, a strong acid, a strong base or a weak acid.

4. For each of the following moles of acid or base add to the buffer in Questions 2 predict what type of solution is formed after the neutralization (use the example above to assist);

a) 0.0050 mol NaOH to the buffer in Q2.

b) 0.00250 mol HCl to the buffer in Q2.

c) 0.050 mol HCl to the buffer in Q2.

d) 0.35 mol NaOH to the buffer in Q2.

 

5. Is there anything about the questions that you feel you do not understand? List your concerns/questions.

6. If there is one question you would like to have answered in lecture, what would that question be?