1. Determination of Ka for a Weak Acid
Experiment 25
Determination of Ka for a Weak Acid
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2. In Lab
Work in groups of 2
NaOH is already prepared; your lab instructor will give you the molarity of the NaOH
Do parts C and D:
part C is the experiment, part D is only calculations
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3. Part C Make sure the starting volume in the buret is exactly 0.00 mL
Buret volume readings should have 2 digits after the decimal point
Use the pH meter to determine the pH of the solution in flask after each addition of titrant.
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4. Part D Calculations only, no lab work. Use the data from part C.
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5. Calculations Part C For each trial: Make a titration curve
Determine the equivalence volume
Determine the (½ equivalence volume)
Determine the pH at the ½ equivalence volume
pKa = pH at the ½ equivalence volume
Ka = 10 –pKa
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6. Calculations Part D For each trial:
The volume of acid is the volume put into the Erlenmeyer flask in part C.
The molarity of NaOH is given by lab instructor.
The mL of NaOH at equivalence pt. is from curve.
M of unknown acid = moles acid / L of acid
Moles acid = moles base = (MNaOH) (L of base)
CHE118