Question

Intr-un litru de H2O se introduc 2,3g Na. Reactia are loc fără variatie de volum. Determinati ph-ul solutiei finale.

Answer 1

2,3 g   a g           b g

2Na + 2H2O => 2NaOH + H2

2x23   2x18       2x40

avem initial 1 L apa = 1000 g apa

=>

a = 2x18x2,3/2x23 = 1,8 g apa consumata in reactie

=> m.apa ramasa = 1000 - a = 1000-1,8 = 998,2 g apa

b = 2x40x2,3/2x23 = 4 g NaOH

=> md = 4 g

Cm = md/miuxVs = 4/40x1 = 0,1 mol/L

NaOH fiind baza tare stim ca Cm = [HO-]

pOH = -lg[HO-] = -lg[Cm]

= -lg[10^-1] = -(-1)x1 = 1

pH + pOH = 14 => pH = 14-pOH

=> pH = 13