Question

Assuming each solution to be 0.10 M , rank the following aqueous solutions in order of decreasing pH.

Answer 1

Answer:

Ba(OH)₂ > NaOH > HCl = HOCl >  N₂H₂

Explanation:

The pH = -log[H⁺] and pOH = -log[OH⁻], and by the water equilibrium, pH + pOH = 14. The value of pH determines the acid-base solutions: for pH< 7 the solution is an acid, for pH > 7 the solution is a base, and for pH = 7 the solution is neutral.

To determine the [H⁺] and the [OH⁻], let's do the dissolution reactions.

a. N₂H₂ → 2N⁻ + 2H⁺

For the stoichiometry (1:2:2), [H⁺] = 2*0.10 = 0.20 M

pH = -log(0.20) = 0.70

b. Ba(OH)₂ → Ba⁺ + 2OH⁻

For the stoichiometry (1:1:2), [OH⁻] = 2*0.10 = 0.20 M

pOH = -log(0.20) = 0.70

pH = 14 - 0.70 = 13.30

c. HOCl → H⁺ + OCl⁻

For the stoichiometry (1:1:1), [H⁺] = 0.10 M

pH = -log(0.10) = 1.00

d. NaOH → Na⁺ + OH⁻

For the stoichiometry (1:1:1), [OH⁻] = 0.10 M

pOH = -log(0.10) = 1

pH = 14 - 1 = 13.00

e. HCl → H⁺ + Cl⁻

For the stoichiometry (1:1:1), [H⁺] = 0.10 M

pH = -log(0.10) = 1.00

Ba(OH)₂ > NaOH > HCl = HOCl >  N₂H₂