What is the pH of 0.00135 mol/L H2SO4(aq) at 25oC? For H2SO4, Ka1 is very large

Question

What is the pH of 0.00135 mol/L H2SO4(aq) at 25oC? For H2SO4, Ka1 is very large and pKa,2=1.96 at 25oC. Give your answer accurate to two decimal places

Explanation / Answer

H2SO4 => H+ + HSO4- [H+]= 0.00109 M = [HSO4-] for the second dissociation : HSO4- H+ + SO42- initial concentration 0.00109, , , , ,, 0.00109 change -x .. . . . . . . . . . . . +x. . . .+x at equilibrium 0.00109-x. . . . .0.00109+x .. . .x Ka2 =10^-1.96 =0.0110 0.0110 = (0.00109+x)(x) / 0.00109-x 1.20 x 10^-5 - 0.0110 x = 0.00109x+x^2 x^2 + 0.0121x - 1.20 x 10^-5=0 x = - 0.0121 + sq.rt (0.000146 + 0.000048)/2=0.000914 [H+]= 0.000914 + 0.00109=0.00200 M pH =2.70

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