chemistry acids and bases

Question

Find the pH and the concentrations of all species (other than water) in the following solutions at 25 °C: (a) 0.30 M HNO3; (b) 0.30 M NaOH; (c) 4.2 × 10−3 M HClO4; (d) 2.9 × 10−4 M Ca(OH)2; (e) 1.0 M NaCl; (f) 0.10 M KNO3.

Answer 1

(a). 0.30 M HNO₃

HNO₃ (strong acid) ==> H⁺ + NO₃^-

[H⁺] = 0.30 M

[NO₃^-] = 0.30 M

pH = -log [H⁺] = -log 0.30 = 0.52

(b). 0.30 M NaOH (strong base) ==> Na⁺ + OH^-

[Na⁺] = 0.3 M

[OH^-] = 0.30 M

pOH = -log [OH^-] = -log 0.30 = 0.52

pH = 14 - 0.52 = 13.48

(c). 4.2x10^-3 M HClO₄ (strong acid) ==> H⁺ + ClO₄^-

[H⁺] = 4.2x10^-3 M

[ClO₄^-] = 4.2x10^-3 M

pH = -log [H⁺] = -log 4.2x10^-3 M = 2.38

(d). 2.9x10^-4 M Ca(OH)₂ (strong base) ==> Ca²⁺ + 2OH^-

[Ca²⁺] = 2.9x10^-4 M

[OH-] = 2 x 2.9x10^-4 M = 5.8x10^-4 M

pOH = -log [OH^-] = -log 5.8x10^-4 M = 3.24

pH = 14 - 3.24 = 10.76

(e). 1.0 M NaCl (neutral salt) ==> Na⁺ + Cl^-

[Na⁺] = 1.0 M

[Cl^-] = 1.0 M

pH = 7

(f). 0.10 M KNO₃ (neutral salt) ==> K⁺ + NO₃^-

[K⁺] = 0.10 M

[NO₃^-] = 0.10 M

pH = 7