Question

determinati concentratia molara a urmatoarelor solutii: a)in 200mL solutie sunt dizolvati 20 moli NaOh; b)in 100 mLsolutie sunt dizolvate 8g NaOh; c)se amesteca 200 g solutie de NaOh 20% (p=1,225 g/cm3)cu 36,74 mL apa;

Answer 1

a)Vs=200 ml=0,2l
nNaOH=20 moli
CM=? 
CM=n/V=20mol/0,2l=100mol/l
b)V=100 ml=0,1 l
m=8 g
Cm=?
MNaOH=23+16+1=40
Cm=m/M*V=8g/40g/mol*0,1l=2mol/l
c)mNaOH=200g
C=20%
ρ=1,225 g/cm3 
VH2O=36,74 ml 
Cm=?
md=c*ms/100=20*200/100=40 g
nNaOH=m/M=40g/40 g/mol=1mol
ρ=m/v  v=m/ρ=40g/1,225 g/cm3=32,65 cm3
V=VNaOH+VH2O=32,65 +36,74=69,39 l
cm=n/V=1mol/69,39 l=0,01 mol/l