Calculate the pH of a 2.0 × 10^-8 M solution of HNO₃. A) 7.70 B) 6.96 C) 7.00 D) 6.30 E) 7.04

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HNO₃ is nitrous acid (HNO2) which is a weak acid. The equilibrium reaction of nitrous acid dissociation is: HNO2 + H2O ⇌ H3O+ + NO2- The acid dissociation constant expression is: Ka = [H3O+][NO2-] / [HNO2] The Ka value of nitrous acid is 4.5 × 10^-4 M. We can use the following pH formula for a weak acid: pH = 1/2(pKa - log([HA])) where HA is the concentration of the weak acid (in this case, nitrous acid) Substituting the values: pH = 1/2(-log(4.5 × 10^-4) - log(2.0 × 10^-8)) pH = 6.96

Calculate the PH of a 2