Piperazine, C4H10N2, is a diprotic weak base (pKb1 = 4.22 and pKb2 = 8.67). A sa
ID: 818123 • Letter: P
Question
Piperazine, C4H10N2, is a diprotic weak base (pKb1 = 4.22 and pKb2 = 8.67). A sample of piperazine is dissolved in 100.0 mL of water and titrated with 0.500 M HCl. It takes 48.00 mL of HCl to reach the second equivalence point.
SHOW ALL WORK
a) What was the original concentration of the piperazine solution?
b) Calculate the pH after the following amounts of HCl have been added: 0 mL, 12.00mL, 24.00mL,36.00mL, 48.00mL, and 60.00mL
c) Sketch the titration curve for this titration
d) Which of the ollowing indicators could be used to detect the first equivalence point? The second?
Indicator Ka Color Change
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Bromocresol green 2.5 x 10^-5 yellow => blue-green
Phenol Red 2.5 x 10^-8 yellow => red
Methyl Yellow 3.5 x 10^-4 red => yellow
Alizarin Yellow 8.9 x 10^-12 yellow => red
Explanation / Answer
Chemical reaction: C4H10N2 (aq) + H+ (aq) ----------------> C4H10N2H+(aq) ( First equivalence point) C4H10N2H+(aq) + H+ (aq) ----------------> C4H10N2H2+(aq) (Second equivalence point) From the balanced chemical reacion one mole of the acid isreacting with one mole of the base. We know that the volume required to reach the first equivalence point and thesecond equivalence point is same. Hence the volume of HCl at the first equivalencepoint = 24.0 mL Data: [HCl] = 0.500 M VHCl = 24.0 mL =0.024 L Number of moles of HCl = 0.024 L * 0.500 M =0.012 moles ? Concentration of Piperazine in 100 mL = 0.012 moles /0.1 L = 0.12 MChemical reaction: C4H10N2 (aq) + H+ (aq) ----------------> C4H10N2H+(aq) ( First equivalence point) C4H10N2H+(aq) + H+ (aq) ----------------> C4H10N2H2+(aq) (Second equivalence point) From the balanced chemical reacion one mole of the acid isreacting with one mole of the base. We know that the volume required to reach the first equivalence point and thesecond equivalence point is same. Hence the volume of HCl at the first equivalencepoint = 24.0 mL Data: [HCl] = 0.500 M VHCl = 24.0 mL =0.024 L Number of moles of HCl = 0.024 L * 0.500 M =0.012 moles ? Concentration of Piperazine in 100 mL = 0.012 moles /0.1 L = 0.12 M