A buffer is prepared from hypochlorous acid (HCIO) and sodium hypochlorite (NaCIO). It contains 0.075 mol of the acid and 0.055 mol of the base in 250. mL of aqueous solution. Calculate the pH of this buffer. (Ka=3.5x10-8

 

The pH is 7.33

Below is the step-by-step explanation for determining pH 

Step-by-step explanation

Data

mol HClO = 0.075 mol

mol NaClO = 0.055 mol

V = 250 mL

Transform volume of mL to L

1 L= 1000 mL

V = 250 mL x?1000mL1L??

V = 0.250 L

A buffer is a solution formed by a weak acid or base and the conjugated salt of this weak acid or base. A buffer is characterized by resisting sudden changes in pH when a strong acid or base is added. The pH of a buffer is calculated using the Henderson Hasselbalch equation 

pH = pka + log [salt]/[acid] (the Henderson Hasselbalch equation )

you must calculate molarity of HClO and NaClO

Molarity is a concentration unit that indicates how many solute moles there are for each liter of solution. the molarity formula is 

M = ?Vmol?? ,

M HClO = ?0.250L0.075mol??

M HClO = 0..30 mol/L

M NaClO = ?0.250L0.055mol??

M HClO = 0.22 mol/L

for buffer the reaction is

HCOl + H₂O ??? ClO^-(aq) + H₃O⁺(aq)

The pH is calculate like

pH = pka + log [salt]/[Acid]

with

[salt]= [NaOCl]= [ClO^-] = 0.22 M

[Acid] = [HClO] = 0.30 M

Ka=3.5x10^-8

pka = -log ka

pka = -log 3.5x10^-8

pka = 7.46

pH = 7.46 + log 0.22/0.30

pH = 7.46 -0.13

pH = 7.33