Question

What volume (in mL) of 1.0 M HCl is required to prepare 1000 mL of pH 7.76 buffer using triethanolamine that is 0.020 M in both triethanolamine and triethanolammonium ion?

Answer 1

[base] =triethanolamine

[salt] = triethanolammonium ion

moles of both salt and base = 0.02 x 1000 / 1000 = 0.02

[salt ] + [base] = 0.02-------------------->1

pH = 7.76

pOH = 6.24

HCl + base ----------------> salt + H2O

pOH = pKb + log [salt / base]

6.24 = 6.2 + log [salt / base]

[salt / base] = 1.096

[salt] = 1.096 [base] ------------------> 2

[base] + 1.096 [base] = 0.02

[base] = 0.0095

[salt] = 0.01 moles

salt moles = HCl moles

HCl moles = 0.01

HCl molarity = moles / volume

1.0 = 0.01 / volume

volume = 0.01 L

volume of HCl = 10ml