Polyethylene is a synthetic polymer or plastic with many uses. 1.36 g of a polye
ID: 1088402 • Letter: P
Question
Polyethylene is a synthetic polymer or plastic with many uses. 1.36 g of a polyethylene sample was dissolved in enough benzene to make 100. mL of solution, and the osmotic pressure was found to be 1.86 torr at 25oC. What is the approximate molar mass of the polyethylene?
A)
179 g/mol
B)
1.14 ´ 104 g/mol
C)
7.35 ´ 103 g/mol
D)
1.24 ´ 105 g/mol
E)
1.36 ´ 105 g/mol
Determine the osmotic pressure of a solution that contains 0.048 g of a hydrocarbon solute (molar mass = 340 g/mol) dissolved in benzene to make a 350-mL solution. The temperature is 20.0°C.
A)
0.50 torr
B)
2.5 torr
C)
3.3 torr
D)
7.4 torr
E)
6.9 torr
Calculate the molarity of a solution containing KCl and water whose osmotic pressure at 21.6°C is 125 torr. Assume complete dissociation of the salt.
A)
0.00680 M
B)
5.17 M
C)
0.0464 M
D)
0.00340 M
E)
0.0928 M
A)
179 g/mol
B)
1.14 ´ 104 g/mol
C)
7.35 ´ 103 g/mol
D)
1.24 ´ 105 g/mol
E)
1.36 ´ 105 g/mol
Explanation / Answer
1)
P= 1.86 torr
= (1.86/760) atm
= 0.0024 atm
T= 25.0 oC
= (25.0+273) K
= 298 K
use:
P = C*R*T
0.0024 = C*0.0821*298.0
C =0.0001 M
volume , V = 100 mL
= 0.1 L
use:
number of mol,
n = Molarity * Volume
= 0.0001*0.1
= 1*10^-5 mol
mass(solute)= 1.36 g
use:
number of mol = mass / molar mass
1*10^-5 mol = (1.36 g)/molar mass
molar mass = 1.36*10^5 g/mol
Answer: E
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