Question

calculati Ph-ul solutiei obtinute prin introducerea a 0.8 g naoh intr-un balon cotat cu volumul de 2000 cm3, completat apoi cu apa distilata pana la semn.

Answer 1

m = 0,8g NaOH
Vs = 2000cm3 = 2L
pH = ?

n = m/M = 0,8/80 = 0,01 moli NaOH

C = n/Vs = 0,01/2 = 0,005 moli/L 

NaOH -> B.T => [NaOH] = C = [OH⁻] = 10⁻(pOH) = 5×10⁻³ M 

Kw = [OH⁻]×[H₃O⁺] = 10⁻¹⁴ (mol/L)² ⇒ [H₃O⁺] = (10⁻¹⁴)/(5×10⁻³) = 0,2×10⁻¹¹ moli/l

pH = -lg[H₃O⁺] = -lg 2×10⁻¹² = 11,69897

Answer 2

[HO⁻] = [NaOH] = (0,8/40)/2 = 0,01 = 10⁻²
[H⁺] = 10⁻¹⁴ /10⁻² = 10⁻¹²
pH = - lg10⁻¹² = 12