<Li> Step 1: K a = 10 − 4.19 = 6.46 × 10 − 5 (\ displaystyle K_ (a) = 10 ^ (- 4.19) = 6.46 \ times 10 ^ (- 5)) </Li> <Li> Step 2: Set up the quadratic equation . (H) 2 + 6 ⋅ 46 × 10 − 5 (H) − 6 ⋅ 46 × 10 − 7 = 0 (\ displaystyle (\ ce (((H) ^ (2)) + (6.46 \ times 10 ^ (- 5) (H)) - 6.46 \ times 10 ^ (- 7) = 0))) </Li> <Li> Step 3: Solve the quadratic equation . (H +) = 7 ⋅ 74 × 10 − 4 (\ displaystyle (\ ce (((H+)) = 7.74 \ times 10 ^ (- 4)))); pH = 3.11 </Li> <P> For alkaline solutions an additional term is added to the mass - balance equation for hydrogen . Since addition of hydroxide reduces the hydrogen ion concentration, and the hydroxide ion concentration is constrained by the self - ionization equilibrium to be equal to K w (H +) (\ displaystyle (\ frac (K_ (w)) (\ ce ((H+))))) </P>

Explain how ph is a measurement of acidity and alkalinity