Puferi
Submitted by Vesna on Thu, 07/03/2014 - 19:32

Forums:
Koliko miligrama CH3COONa treba dodati u 100 cm(3) rastvora CH3COOH koncentracije 0,5 mol/L da bi se dobio pufer ciji je pufer ciji je pH 4? K(CH3COOH)=2x10(-5)
Resenje je 820.
CH3COOH------------------
CH3COOH------------------>CH3COO- + H+
Ka={CH3COO-}*{H+}/{CH3COOH}
2*10(-5)=n(CH3COO-)*1*10(-4)/0.05
n(CH3COOH)=(CH3COOH)*V=0.5*0.1=0.05 mol
{H+}=1*10(-4) mol/l jer je pH=4
n(CH3COO-)=1*10(-6)/1*10(-4)=0.01 mol
CH3COONa----------------->CH3COO- + Na+
n(CH3COONa)=n(CH3COO-)=0.01 mol
m(CH3COONa)=n(CH3COONa)*Mr=0.01*82=0.82 g=820 mg