Puferi

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

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milicaradenkovic - Fri, 07/04/2014 - 07:11

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