IV. Comparing Buffering Capacity A. pH of Pure Water i. Measure out 30.0 mL DI H
ID: 1020320 • Letter: I
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 ____
Explanation / Answer
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 __________
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