1. The vapor pressure of ethanol (C2H5OH) at 20°C is 44 mmHg, and the vapor pres
ID: 534668 • Letter: 1
Question
1. The vapor pressure of ethanol (C2H5OH) at 20°C is 44 mmHg, and the vapor pressure of methanol (CH3OH) at the same temperature is 94 mmHg. A mixture of 28.1 g of methanol and 45.9 g of ethanol is prepared and can be assumed to behave as an ideal solution.
Calculate the vapor pressure of methanol and ethanol above this solution at 20°C. Be sure to report your answers to the correct number of significant figures.
Ethanol: ____mmHg
Calculate the mol fraction of methanol and ethanol in the vapor above this solution at 20°C.
Methanol _____
Ethanol _____
2.
[CH2(OH)CH2(OH)] would you add to a car radiator containing 7.50 L of water if the coldest winter temperature in your area is 20.5°C? Calculate the boiling point of this water-ethylene glycol mixture. (The density of ethylene glycol is 1.11 g/mL.)
°C
3. Calculate the percent by mass of the solute in each of the following solutions:
(a) 5.03 g of NaBr in 71.1 g of solution
% NaBr
(b) 32.5 g of KCl in 183 g of water
% KCl
(c) 3.81 g toluene in 33.1 g benzene
% toluene
How many liters of the antifreeze ethylene glycol
[CH2(OH)CH2(OH)] would you add to a car radiator containing 7.50 L of water if the coldest winter temperature in your area is 20.5°C? Calculate the boiling point of this water-ethylene glycol mixture. (The density of ethylene glycol is 1.11 g/mL.)
What is the volume of antifreeze?
L
What is the boiling point of the solution?
°C
Explanation / Answer
Ans 1. The molar mass of Methanol =32.04 g / mol
Number of moles of Methanol =28.1 / 32.04 = 0.878 moles
Molar mass of Ethanol = 46.07 g / mol
Number of moles of Ethanol= 45.9 / 46.07 = 0.996 moles
Mole fraction of Methanol = 0.878 / ( 0.878 + 0.996) = 0.469
Partial vapour pressure of Methanol = 94 x 0.469 = 44.07 mmHg
Mole fraction of Ethanol=0.531
Partial vapour pressure of Ethanol = 44 x 0.531= 23.36 mmHg
Total vapour pressure of the solution = 44.07 + 23.36 = 67.4 mm Hg
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