Piperazine, HN(C4H8)NH, is a diprotic weak base used as a corrosion inhibitor an

ID: 484493 • Letter: P

Question

Piperazine, HN(C4H8)NH, is a diprotic weak base used as a corrosion inhibitor and an insecticide and has the following properties:

pKb1=4.22pKb2=8.67

For writing the reactions of this base in water, it can be helpful to abbreviate the formula as Pip:

Pip+H2OPipH++H2OPipH++OHPipH22++OH

The piperazine used commercially is a hexahydrate with the formula C4H10N26H2O.

A 0.00515-mol sample of piperazine hexahydrate is dissolved in enough water to produce 100.0 mL of solution and is titrated with 0.500 MHCl.

Calculate the pH when 12.875 mL of HCl has been added.

mol = 0.00515

V = 100 mL = 0.1 L

M = ml/V = 0.00515/0.1= 0.0515 mol per liter = 51.5 mmol of

mol of HCL = MV = 0.5*12.875 = 6.4375 mmol of HCl

this will becme a buffer:

mmol of base left = 51.5 -6.4375 = 45.0625

mmol of conjugate formed = 6.4375

the buffer equation

pOH = pKb1 + log(HB+/B)

pOH = 4.22 + log(6.4375/45.0625) = 3.3749

pH = 14-pOH = 14-3.3749

pH = 10.6251