Question

What is the pH of a solution containing 0.155 mol/l of CH3COO- and 0.025 mol/l of HCL? (pKa of CH3COO- & CH3COOH is 4.76)

Answer 1

we use following formulae to calculate the pH of solution

[H₃O⁺] = c2+{(c₂)² + 4 Ka c₁} / 2 where c2 = concerntration of weak acid ,

c1= concerntration of strong acid , Ka = equillibrium constant for weak acid

now putting values we get

[H₃O⁺] =   0.155   +{(0.155)² + 4 *4.76 * 0.025 } / 2

= 0.155 +   (0.024 + 0.476 )/2

= 0.155 + 0.5 /2 =

= (0.155 +  0.7 )/2 = 0.4275 mol/lit

pH= - log [H₃O+] = -log [0.425] = - log (4.25 * 10^-1) = -log 4.25 - log 10^-1

pH = 0.628 +1 = 1.628