How many millimoles of solid NaOH must be added to 50.0 milliliters?

Question

of 0.20 molar HOCl to obtain a buffer solution that has a pH of 7.49?

Answer 1

pKa of HClO = 7.49

pH = pKa + log [ClO-] / [HClO]

7.49 = 7.49 + log [ClO-] / [HClO]

[ClO-] / [HClO] = 1.0

HClO + OH- >> ClO- + H2O

Moles HClO = 0.0500 L x 0.20 =0.01

Moles OH- needed to get [ClO-] = [HClO] = 0.01 / 2 =0.0050 = 5.0 mmol

in this way we get 0.005 moles of HClO and 0.005 moles of ClO-

they have the same concentration so their ratio is 1