Name: Chem 8B Post Lab Questions Lab XI Synthesis of 2-Chloro-2-methylbutane . L

Question

Name: Chem 8B Post Lab Questions Lab XI Synthesis of 2-Chloro-2-methylbutane . Look at the graph on pg, 80 of your lab manual to answer the following questions. a. Compound A and compound B mix to form an ideal solution. These mixtures -minimum and will boil between what two temperatures maximum. A solution contains 2.1 mol A and 7.9 mol of B and has a boiling point of 82.0°C at 760. Torr. b. i. What is the vapor pressure of pure A at 82.0°C? ii. What is the vapor pressure of pure B at 82.0°c? ii What is the vapor pressure of A in the mix at 82.0°C? iv. What is the vapor pressure of B in the mix at 82.0°C? v. What is the mol fraction A in the vapor? - ' v, what is the mol fraction B in the vapor? vii. What is the mol fraction A in the liquid? vii. What is the mol fraction B in the liquid? ix. The vapor is enriched in (circle one): COMPOUND A COMPOUND B NEITHER BOTH

Explanation / Answer

1. The nomal boiling point of A is 50 deg.c and that of B is 100 deg.c. So a mixture forming ideal solution starts boilong at 50 deg.c (minimum)and boiling is complee at 100 deg.c.

2.from the plot draw a vertical line at 82 deg.c, where ever it intersect curves A, from there draw horizontal line to meet the pressrue axis which gives the vapor pressure of A at that temperature. the vapor pressure of A is 1900 torr and similar exercies done for B gives a vapor pressure of 460 torr

3. mole fraction of A, x1= moles of A/ total moles= 2.1/(2.1+7.9)=0.21, mole fraction of B,x2= 0.79

since the solution forms vapor pressure of A in the mix= mole fraction of A* pure component vapor pressure of A=0.21*1900=399 Torr, vapor pressure of B in the mix= 0.79*460=363 mm Hg

.mole fraction in the vapor phase : A = mole fraction A* pure component vapor pressure of A/ total pressure = 0399/760 =0.53, mole fraction of B in the vapor phase= 1-0.53=0.47

mole fraction of A in the liquid phase=0.21, that of B =0.79

The vapor is enriched in A since it is having more vapor pressure compared to B at the same temperature and higher the vapor pressure, more is the tendency to get into the vapor phase.

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