he vapor pressures of several solutions of water-propanol(Ch3Ch2Ch2OH) were determined at various compositions, with thefollowing data collected at 45C:
XH2O Vapor pressure (torr)
0 74.0
.15 77.3
.37 80.2
.54 81.6
.69 80.6
.83 78.2
1.00 71.9
a.) Are solutions of water and propanol ideal? explain.
b.) predict the sign of ^Hsoln (delta H soln) forwater-propanol solutions.
c.) Are the interactive forces between propanol and watermolecules weaker than, stronger than, or equal to the interactiveforces between the pure substance? Explain.
d.) Which of the solutions in the data would have the lowestnormal boiling point?
a.) To determine if solutions of water and propanol are ideal, we can compare the measured vapor pressures to the expected values based on Raoult's law. According to Raoult's law, the vapor pressure of a component in an ideal solution is proportional to its mole fraction in the solution. If the measured vapor pressures match the expected values based on Raoult's law, then the solution can be considered ideal.
To check if the solutions are ideal, we can calculate the expected vapor pressure of propanol using the mole fraction of propanol in each solution. For example, at XH2O = 0.15, the mole fraction of propanol (Xpropanol) would be 1 - XH2O = 1 - 0.15 = 0.85. We can then multiply this mole fraction by the vapor pressure of pure propanol (71.9 torr) to get the expected vapor pressure of propanol in the solution:
Expected vapor pressure of propanol = Xpropanol * Vapor pressure of pure propanol.
Comparing this expected vapor pressure with the measured vapor pressure (77.3 torr), we can determine if the solution is ideal. Repeat this calculation for other compositions and compare the expected and measured vapor pressures for each solution.
b.) The sign of ΔHsoln (delta H soln) for water-propanol solutions can be predicted based on the intermolecular forces between the solute (propanol) and the solvent (water). If the forces between the solute and solvent are stronger than the forces between the solvent molecules or if they form stronger intermolecular interactions upon mixing, the solute dissolves exothermically and ΔHsoln will be negative. Conversely, if the forces between the solute and solvent are weaker than the forces between the solvent molecules or if they form weaker intermolecular interactions upon mixing, the solute dissolves endothermically and ΔHsoln will be positive.
c.) To determine if the interactive forces between propanol and water molecules are weaker than, stronger than, or equal to the interactive forces between the pure substances, we need to consider the types of intermolecular forces involved. Water molecules can form hydrogen bonds with each other due to the presence of polar O-H bonds. Propanol molecules also have polar O-H bonds and can form hydrogen bonds with water. Therefore, the interactive forces between propanol and water molecules are similar in strength to the interactive forces between water molecules themselves.
d.) The boiling point of a solution depends on the vapor pressure of the solution at a given temperature. A lower vapor pressure corresponds to a lower boiling point. By examining the data, we can observe that the solution with the lowest vapor pressure is likely to have the lowest boiling point.
In this case, we look for the solution with the highest measured vapor pressure, which is at XH2O = 0 (pure water) with a vapor pressure of 74.0 torr. This means that pure water has the highest boiling point.
Therefore, the solution with the lowest normal boiling point would be the one with the highest vapor pressure, which is the pure water solution (XH2O = 0).