- In order to determine the molecular weight of a particular protein, 0.010 g of the protein
was dissolved in water to make 2.93 mL of solution. The osmotic pressure was
determined to be 0.821 torr at 20.0°C. What is the molecular weight of the protein?
A. 3.8 × 103 g/mole
B. 7.6 × 103 g/mole
C. 3.8 × 104 g/mole
D. 7.6 × 104 g/mole
E. None of the above
Answer: D
Begin with the equation
MW = gRT/πV
..
0 010 0 0821
1
293
0 821
1
293
1
1
760
1
g 1000
mole K
liter atm K
torr mL atm
torr
liter
mL
# :
:
= #####
= 7.6 × 104 g/mol
- A solution of NH 3 dissolved in water is 10.0 m. What is the mole fraction of water in
the solution?
A. 1.00/1.18
B. 1.00/2.18
C. 0.18/1.00
D. 0.18/10.0
E. 1.18
Answer: A
This problem can be solved using the factor-label method:
..
.
.
kg H O
moles NH
gH O
kg H O
mole H O
gH O
mole H O
mole NH
1
10 0
1000
1
1
18 02
100
0 180
2
3
2
2
2
2
2
##=^3
total number of moles = 0.180 mole NH 3 + 1.00 mole H 2 O= 1.18 moles sol’n
mole fraction of water = 118100 .. mole sol’nmole H O^2
Part II: Specific Topics