Upload
evina-nathalia
View
228
Download
6
Embed Size (px)
DESCRIPTION
sifat koligatif
Citation preview
MOLALITY AND MOLE FRACTION
COLLIGATIVE PROPERTIES OF
SOLUTION
Why???
Although involving colligative
properties of the solution, colligative
properties do not depend on the
interaction between solvent and
solute molecules, but in
dependence on the amount of
solute dissolved in a solution.
MOLALITY
Molality is the number of moles of
solute in 1 kg (1000 grams) of solvent .
Example
Determine the molarity of solution that
produce 3 grams urea in 200 grams
water????
Answer :
Mole of urea= 3 g/60 g mole -1
Mass of solvent= 200 g =0.2 kg
m= n/p
=0.05/0.2
=o.25 mol kg-1
example
A total of 1.8 g of glucose, C6H12O6
dissolved in 100 grams of water (Ar C = 12, H
= 1, O = 16). Determine the molality of the
glucose solution!
Mole fraction
Mole fraction (X) is ratio of the number of moles
of solute or solvent to the number of moles of
solution.
example
In 100 grams of 20% urea solution
contained 20 grams of urea and 80
grams of water. Determine the moles of
urea fraction
Answer:
Mole of water= 80 g/18 g mole-1
= 4.44 mole
Mole of urea = 20 g/60 g mole-1
= 0.33
Xurea = XB= 0.33/4.44+0.33= 0.069
example
A total of 27.6 grams of ethanol
C2H5OH dissolved in 54 grams of
water (Ar C = 12, H = 1, O = 16).
Calculate the mole fraction mole
fraction of ethanol and water!
answer
Mr.C2H5OH = 46 gr/mol
Mr.H2O = 18 gr/mol
n.C2H5OH = 27,6 gr/(46 gr/mol)
n.H2O = 54 gr/(18 gr/mol)
χ etanol = 0,6 mol/(0,6 mol + 3 mol)=0,167
χ Air = 3 mol/(0,6 mol + 3 mol) = 0,833
exercise
1. Determine the amount (grams) of
NaOH must be dissolved in 1 liter of
water (water = 1.00 g / mL) to obtain
0.25 m NaOH.
2. In 100 grams of 20% urea solution
contained 20 grams of urea and 80
grams of water. Determine the moles of
urea fraction.
Cont.
3. Determine the mole fraction of
solute (Mr=60) in urea solution 10
%
4. Determine the percentage of urea
in urea solution 1 m
5.Determine the mole fraction of 2
molal of urea solution
Remember !!!!!!!!!!!!
Collect your assignment next week
:D