E. pH of Buffer after the addition of the Strong Acid Measure out 50.0 mL the bu
ID: 1048434 • Letter: E
Question
E. pH of Buffer after the addition of the Strong AcidMeasure 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 ____4.42___
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 _4.61______
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 a Buffer Solution after addition of a Strong acid or a strong base. Preparation of a buffer solution: i. Measure out 50.0 mL 1.0 M CH COOH and 50.0 mL of 1.0 M NaCH, COO into a beaker ii. Rinse the pH probe with DI H20 and place it into the solution in the beaker ensuring that the tip is completely immersed. ii. After the pH value on the MeasureNet display has stabilized, record this value on the provided data sheet. iv. Remove the pH probe, rinse it, and place it in the waste beaker until you need it again to ensure that the electrode remains hydrated. pH of the Buffer after the addition of the Strong Acid: v. Measure out 50.0 mL the buffer in part D and add 2.0 mL of 1.0 M HCI into a clean beaker. vi. Rinse the pH probe with DI H2O and place it into the solution in the beaker ensuring that the tip is completely immersed. provided data sheet. ensure that the electrode remains hydrated. Empty the solution into the waste beaker vii. After the pH value on the MeasureNet display has stabilized, record this value on the vii.Remove the pH probe, rinse it, and place it in the waste beaker until you need it again to
Explanation / Answer
If HCl is added to acetate buffer, it will react with CH3COONa to convert it to acetic acid. So, moles of HCl added has to be substracted from acetate and added to acetic acid.
Moles of acetate initially present = 50 *1/1000 = 0.05 moles
moles of acetic acid initially present = 50 *1/1000 = 0.05 moles
Moles of HCl added = 2mL *1/1000 = 0.002 moles
moles of acetate present after addition of HCl = 0.05-0.002 = 0.048 moles
moles of acetic acid present after addition of HCl = 0.05+0.002 = 0.052 moles
pH = pka + log [acetate/acetic acid] = 4.74 + log [0.048/0.052] = 4.70
measured pH = 4.42
% error = 4.70-4.42/4.42 *100 = 6.33 %
Possible source of error is wrong measurement in making the buffer
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