What is the pH of a 25 ml sample of 0.2 M sulfuric acid? What is the pH after 5 ml of 0.25 M sodium hydroxide is added?
H2SO4 fully dissociates into ions (strong acid). It is diprotic therefore concentration of H+ ions is twice that of the acid = 0.4 M. pH = -log[H+] = -log[0.4] = 0.3979... = 0.40 to 2 d.pOH- ions react with H+ ions to produce water. Therefore (moles of H+) - (moles of OH+) = (moles of H+ remaining in solution).= 5 x 10-3 moles (of H+) - 1.25 x 10-3 moles (of OH-) = 3.75 x 10-3 moles remaining.Conc. of H+ = n/V = 0.125 M. pH = -log[0.125] = 0.90 to 2 d.p
