Study guide for my exam. I need help understanding 22-26. Questions on the exam
ID: 1015630 • Letter: S
Question
Study guide for my exam. I need help understanding 22-26. Questions on the exam will be similar.
e 22 Which statement below regarding vapor pressure is not correct? a Vapor pressure is an intensive property b. The suhstance with the stronger intermolecular forces has the lower vapor pressure c. Vapor pressure increases with increasing temperature d Pure water has a higher vapor pressure at a given temperature than seawater e. A nonvolatile solute increases the vapor pressure of the solvent 23. A solution is prepared by adding 1.50 mol glucose, which is not volatile, to 3.50 mol water. What is the vapor pressure of this solution at 2S'C given that the vapor pressure of pure water is 23.8 tor a. 7.00 torr b. 16.7 torr c 10.2 torr d. 7.14 torr c. 34.0 torr 24. A solution is prepared by adding 0.300 mol glucose, which is not volatile, to 4.50 mol water. What is the vapor pressure of this solution at 25°C given that the vapor pressure of pare water is 23.8 tor? a. 9.38 torr b. 22.3 torr c. 23.4 torr d. 1.49 torr e. 22.5 torr 25. A solution contains 6.50 ml water, 0.300 mol sucrose, and 0.200 mol glucose The solutes are nonvolatile. What is the vapor pressure of the solution at 35°C given that the va a. 35.0 torr b. 36.0 tor c 37.0 torr por pressure of water is 42.2 torr? of the solution at 35°C given that the vapor pressure of d 39.2 torr e. 39.0 torr A solution is prepared by mixing 50 g of methanol (a loll) with 50 g of ethanol (akHOH). Use the following data to determine the vapor pressure of this solution at 20 C 26, SK Substance Vapor Pressure at 20°C (torr) 92 45 Methanol Ethanol a. 69 torr b. 57 torr d. 73 torr e83torr 27. The solution is prepared by mixing 75 g of methanol (CIHOH) with 25 g of ethanol (CHsCHOH) Use the SKip following data to determine the vapor pressure of this solution at 20°C Vapor Pressure at 20C (torr) 92 45 Substance Methanol Ethanol a. 69 torr b. 57 torr c. 80 torr d 73 torT e. 83 torr
Explanation / Answer
a)
Intensive propery is independent of mass. When ever vapor pressure is specified, one does not say that vapor presssuee of 1 gm or 2gm. So vapor pressure is independent of mass and hence an intensive property.
Stronger interactions between molecules hold them together prevening to reach the vapor phase. Hence less vapor pressure.
Vapor pressure increases with temperature as
lnP is proportioanal to 1/T, where T is the absoulte temperature in K
Sea water contains dissolved solids which increases the boiling point. Boiling point increases means the less vapor presssure of sea water.
A non volatile solute increases the boiling point and hence vapor pressure decreases. Hence E is the incorrect statement.
b)
Non volatile brings in reduction in vapor pressure
Vapor pressure of component in solution= moles fraction of the component* Pure component vapor pressure
Mole fraction of water= Moles of water/ Total moles = 3.5/(1.5+3.5)= 3.5/5= 0.7
Vapor pressure of solution = 0.7*23.8= 16.7 Torr ( B is correct)
c)
There are 0.3 moles of glucose and 0.45 moles of water.
Vapor pressure of component in solution= moles fraction of the component* Pure component vapor pressure
Vapor pressire of solution = (4.5/(4.5+0.3)*23.8= 22.3 ( bi is correct)
d)
Mole fraction of water= 6.5/(6.5+0.3+0.20)= 6.5/7 =0.93
Vapor pressure of soution = 0.93*42.2=39 torr ( e is correct)
e)
Vapor pressure of solution = mole fraction of ethanol* pure component vapor pressure of ethanol + mole fraction of methanol* pure component vapor pressure of methanol
Moles = mass/Molecular weight
Molecular weights : Ethanol (C2H5OH)= 46, Methanol (CH3OH)= 32
Moles : Ethanol= 50/46= 1.1 , methanol= 50/32=1.56
Total moles = moles of methanol + moles of ethanol= 1.56+1.10= 2.66
Mole fractinos : ethanol = 1.1/2.66 =0.41, ethanol= 1-0.41=0.59
Vapor pressure of solution = 0.41*45+0.59*92=73 torr ( d is correct)
f)
Vapor pressure of solution = mole fraction of ethanol* pure component vapor pressure of ethanol + mole fraction of methanol* pure component vapor pressure of methanol
Moles = mass/Molecular weight
Molecular weights : Ethanol (C2H5OH)= 46, Methanol (CH3OH)= 32
Moles : Ethanol= 25/46= 0.54 , methanol= 75/32=2.34
Total moles = moles of methanol + moles of ethanol= 0.54+2.34= 2.88
Mole fractinos : ethanol = 0.54/2.88= 0.19, ethanol= 1-0.41=0.81
Vapor pressure of solution = 0.19*45+0.81*92=83 torr ( e is correct)