Experiment F: a Raoult’s Law Experiment
Physical Chemistry
CHM2330
Experiment F- Raoult 's Law Experiment
By: Sanah Assaad
Student Number: 5267864
Partner: Jihad Arafa
T.A: Didier
University of Ottawa
March 25, 2010
Objective:
The purpose of this experiment is to study the total vapour pressure of ideal or non-ideal mixtures of two volatile liquids as a function of chemical composition.
Introduction:
For ideal mixtures of volatile liquids the vapour pressure of any given mixture may be obtained by applying Raoult 's Law to each of the components of the mixture. If, for example, pA* and pB* are the vapour pressures of pure compound A and B respectively, and A and B are their mole fractions in a particular mixture, then the partial vapour pressures of each component over that mixture at a given temperature are: pA = A pA* and pB = B pB* and the total vapour pressure is given by the sum of these partial vapour pressures: pT = pA + pB.
Liquid mixtures that obey Raoult 's Law essentially define an ideal solution. This means that the presence of A in B has no effect on the vapour pressure of B except by diminishing the number of moles of B present in each unit volume. This can only result when the forces between molecules of A and B are essentially the same as those between A molecules themselves, and B molecules themselves.
If the attractive forces between A and B are greater than those between A - A and B - B, then both A and B will exhibit partial pressures PA and PB less than those expected from Raoult 's Law. This results in a negative deviation (from that calculated with Raoult 's Law) in the total pressure. On the other hand, if the attractive forces between A and B are less than those between A - A and B - B, then both A and B will exhibit partial pressures PA and PB greater than those expected from Raoult 's Law. This results in a positive deviation in the total pressure. These deviations can be quite small, but for some mixtures are large enough that the total
CHM2330
Experiment F- Raoult 's Law Experiment
By: Sanah Assaad
Student Number: 5267864
Partner: Jihad Arafa
T.A: Didier
University of Ottawa
March 25, 2010
Objective:
The purpose of this experiment is to study the total vapour pressure of ideal or non-ideal mixtures of two volatile liquids as a function of chemical composition.
Introduction:
For ideal mixtures of volatile liquids the vapour pressure of any given mixture may be obtained by applying Raoult 's Law to each of the components of the mixture. If, for example, pA* and pB* are the vapour pressures of pure compound A and B respectively, and A and B are their mole fractions in a particular mixture, then the partial vapour pressures of each component over that mixture at a given temperature are: pA = A pA* and pB = B pB* and the total vapour pressure is given by the sum of these partial vapour pressures: pT = pA + pB.
Liquid mixtures that obey Raoult 's Law essentially define an ideal solution. This means that the presence of A in B has no effect on the vapour pressure of B except by diminishing the number of moles of B present in each unit volume. This can only result when the forces between molecules of A and B are essentially the same as those between A molecules themselves, and B molecules themselves.
If the attractive forces between A and B are greater than those between A - A and B - B, then both A and B will exhibit partial pressures PA and PB less than those expected from Raoult 's Law. This results in a negative deviation (from that calculated with Raoult 's Law) in the total pressure. On the other hand, if the attractive forces between A and B are less than those between A - A and B - B, then both A and B will exhibit partial pressures PA and PB greater than those expected from Raoult 's Law. This results in a positive deviation in the total pressure. These deviations can be quite small, but for some mixtures are large enough that the total
References: 1. Atkins’ Physical Chemistry 8th edition 2. CHM 2330 Physical Chemistry Lab manual (2008) 3. http://chsfpc5.chem.ncsu.edu/~franzen/CH431/lecture/lec_15_solutions.htm 4. http://www.chem.arizona.edu/~salzmanr/480a/480ants/vpdiag&/vpdiag&.html 5. http://en.wikipedia.org/wiki/Dalton%27s_law 6. http://en.wikipedia.org/wiki/Raoult%27s_law 7. http://www.engineersedge.com/fluid_flow/fluid_data.htm 8. http://www.simetric.co.uk/si_liquids.htm