Question

IV. Comparing Buffering Capacity

A. pH of Pure Water

i. Measure out 30.0 mL DI H2O into a beaker.

1. Calculate the expected pH of pure water.                        pH ________

2. Measured pH of pure water.                                                 pH ___3.88______

3. What is the percent error between the calculated and measured value? What are some of the possible sources of this error?

% error __________

B. pH of Water and Strong Acid

i. Measure out 30.0 mL DI H2O and 2.0 mL of 1.0 M HCl into a beaker.

1. Calculate the expected pH of this solution.                      pH _________

2. Measured pH of this solution.                                               pH ___1.64______

3. What is the percent error between the calculated and measured value? What are some of the possible sources of this error?

% error ____

C. pH of Water and Strong Base

i. Measure out 30.0 mL DI H2O and 2.0 mL of 1.0 M NaOH into a beaker.

1. Calculate the expected pH of this solution.                      pH _________

2. Measured pH of this solution. pH __12.03_______

3. What is the percent error between the calculated and measured value? What are some of the possible sources of this error?

% error ____

D. pH of Buffer solution

i. Measure out 50.0 mL 1.0 M CH3COOH and 50.0 mL of 1.0 M NaCH3COO into a beaker.

1. Calculate the total volume. (include units)      Vol __________

2. What is the concentration of acetic acid in this solution after mixing. (include units)

[CH3COOH] _________

3. What is the concentration of acetate ion in this solution after mixing. (include units)

[CH3COO-] ___________

4. Calculate the expected pH of this buffer solution.                        pH __________

5. Measured pH of this buffer solution.                                                 pH __4.56________

6. What is the percent error between the calculated and measured value? What are some of the possible sources of this error?

% error __________

E. pH of Buffer after the addition of the Strong Acid

Measure out 50.0 mL the buffer in part D and add 2.0 mL of 1.0 M HCl into a clean beaker.

1. Calculate the expected pH of this solution.                      pH _________

2. Measured pH of this solution.                                               pH ____5.30_____

3. What is the percent error between the calculated and measured value? What are some of the possible sources of this error?

% error ____

F. pH of Buffer after the addition of the Strong Base

Measure out 50.0 mL the buffer in part D and 2.0 mL of 1.0 M NaOH into a clean beaker.

1. Calculate the expected pH of this solution.                      pH _________

2. Measured pH of this solution. pH _4.57________

3. What is the percent error between the calculated and measured value? What are some of the possible sources of this error?

% error ____

Answer 1

IV. Comparing Buffering Capacity

A. pH of Pure Water

i. Measure out 30.0 mL DI H2O into a beaker.

1. Calculate the expected pH of pure water.                        pH ______7.00__

2. Measured pH of pure water.                                                 pH ___3.88______

3. What is the percent error between the calculated and measured value? What are some of the possible sources of this error?

% error __________ (7.00-3.88/7.000)*100

= 44.57 %

Percentage error = (measured value- actual value / actual value )*100

B. pH of Water and Strong Acid

i. Measure out 30.0 mL DI H2O and 2.0 mL of 1.0 M HCl into a beaker.

Total volume = 32 ml = 0.032 L

Moles of H+= 1.0 moles/1000 ml*2.0 ml

= 2.0*10^-3

Molarity = 2.0*10^-3/0.032 = 0.0625 M

pH = - log [H+] = 1.20

1. Calculate the expected pH of this solution.                      pH ____1.20_____

2. Measured pH of this solution.                                               pH ___1.64______

3. What is the percent error between the calculated and measured value? What are some of the possible sources of this error?

1.20-164/1.20)*100

=-36.6%

% error ____

C. pH of Water and Strong Base

i. Measure out 30.0 mL DI H2O and 2.0 mL of 1.0 M NaOH into a beaker.

Total volume = 32 ml = 0.032 L

Moles of OH-= 1.0 moles/1000 ml*2.0 ml

= 2.0*10^-3

Molarity = 2.0*10^-3/0.032 = 0.0625 M

pOH = - log [OH-] = 1.20

pH = 14-pOH = 14-1.20= 12.80

1. Calculate the expected pH of this solution.                      pH ____12.8_____

2. Measured pH of this solution. pH __12.03_______

3. What is the percent error between the calculated and measured value? What are some of the possible sources of this error?

[(12.8-12.03)/12.8]*100     

=6.02%

% error ____

D. pH of Buffer solution

i. Measure out 50.0 mL 1.0 M CH3COOH and 50.0 mL of 1.0 M NaCH3COO into a beaker.

1. Calculate the total volume. (include units)      Vol ___100 .0 ml_______

2. What is the concentration of acetic acid in this solution after mixing. (include units)

Number of moles of CH3COOH = 1.0* 0.050 L

= 0.05 Moles

[CH3COOH ] = Number of mole s/ total volume = 0.05/0.100 = 0.5 M

[CH3COOH] _= ________

3. What is the concentration of acetate ion in this solution after mixing. (include units)

Number of moles of CH3COONa = 1.0* 0.050 L

= 0.05 Moles

[CH3COONa ] = Number of mole s/ total volume = 0.05/0.100 = 0.5 M

[CH3COO-] ___=0.5 M________

4. Calculate the expected pH of this buffer solution.                        pH __________

pH = pKa + log [salt]/[acid]

pH = 4.7+ log 0,5/0.5

= 4.7

5. Measured pH of this buffer solution.                                                 pH __4.56________

6. What is the percent error between the calculated and measured value? What are some of the possible sources of this error?

4.7-4.56/4.7)*100

= 2.98%

% error __________