pH

marank's picture

koliki je pH rastvora koji u 500 mililitara sadrzi 51 g NH3 i 196 g NH4Br.K(NH3)=(1.8X10^-5.

milicaradenkovic's picture

n(NH3)=m/Mr=51/17=3 mol

n(NH4Br)=m/Mr=196/98=2 mol

NH4Br----------------->NH4+ + Br-

n(NH4+)=n(NH4Br)=2 mol

NH4+ + H2O---------------->NH3+H3O+

Kb={NH3}*{H3O+}/{NH4+}

c(NH3)=n(NH3)/V=3/0.5=6 mol/l

c(NH4+)=n(NH4+)/V=2/0.5=4 mol/l

1.8*10(-5)=6*{H3O+}/4

{H3O+}=7.2*10(-5)/6=1.2*10(-5) mol/l

pH= -log{H3O+}=4.92