Part B: Give two specific source of error that could occur during the titration

Question

Part B: Give two specific source of error that could occur during the titration and explian in detail

Part C: write out the second base dissociation reaction and determine the value for Kb2 for this acid/conjugate base system [Ka1=4.65e-6 ; Ka2=1.86e-10)

. A 24.97 mL sample of piperazine (a diprotic acid, H2Pip) was titrated with 0.01206 M NaOH. A 50.00 mL portion of the NaOH was added, which was enough to overshoot the second equivalence point. Any remaining NaOH in solution was then titrated requiring 10.78 mL of standardized solution of HNO3 with a concentration of 0.03145 M. a. (a2 pts) What is the concentratón of piperazine in the original sample? (12 pts) What is the concentration of piperazine in the original sample? a.

Explanation / Answer

Part B

1) Inaccuracy in the concentartion of the standard solution: If concentration of the titrant NaOH is not accurate i.e if it has some contamination, this would alter (lower) its concentartion which would affect the molarity calculations.

2) If you overshoot the endpoint: This would result in an increase in the volume of the titrant added which would then lower the calculated molarity.

Part C

Formula to use:

Ka * Kb = Kw

Kb = Kw/Ka

Ka= acid dissociation constant

Kb = base dissociation constant

Kw= dissociation constant for H2O = 10^-14

First base dissociation:

H2Pip + H2O ----------- H2PipH^+ + OH^-

Second base dissociation:

H2PipH^+ + H2O ------- H2PipH^2+ + OH^-

Kb2 = Kw/Ka2 = 10^-14 / 1.86 * 10^-10 = 5.38 * 10^-5

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