The 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 whether the solutions of water and propanol are ideal, we can compare the observed vapor pressure values with the expected ideal vapor pressure values. In an ideal solution, the vapor pressure follows Raoult's Law, which states that the vapor pressure of a component in a solution is proportional to its mole fraction in the solution.
If the solutions are ideal, the observed vapor pressure should be equal to the product of the vapor pressure of water (PH2O) and its mole fraction (XH2O), added to the product of the vapor pressure of propanol (PPropanol) and its mole fraction (XPropanol).
Let's calculate the expected vapor pressures using Raoult's Law:
XH2O PH2O (torr) XPropanol PPropanol (torr) Expected Vapor Pressure (torr)
0 74.0 1.0 0 0.0
0.15 74.0 0.85 ? ?
0.37 74.0 0.63 ? ?
0.54 74.0 0.46 ? ?
0.69 74.0 0.31 ? ?
0.83 74.0 0.17 ? ?
1.0 74.0 0.0 73.6 73.6
By comparing the expected vapor pressures with the given data, we can determine if the solutions are ideal.
b.) The enthalpy of solution (ΔHsoln) can be predicted based on the interactions between the solute and solvent molecules. If the interactions are stronger in the solution than in the pure substances, energy will be released when the solute dissolves, resulting in a negative ΔHsoln. Conversely, if the interactions are weaker, energy will be absorbed, resulting in a positive ΔHsoln.
c.) To determine if the interactive forces between propanol and water molecules are weaker, stronger, or equal to the interactive forces between the pure substances, we need to examine the observed vapor pressures at different compositions. If the observed vapor pressures are higher or lower than the expected values, it indicates potential changes in the interactions.
d.) The solution with the lowest normal boiling point corresponds to the composition with the highest vapor pressure. We can examine the given data to identify the solution with the highest vapor pressure.
Let's analyze the given data step by step.
To answer these questions, we need to analyze the provided data and apply relevant concepts. Let's go through each question step by step:
a.) To determine if a solution is ideal, we need to compare its behavior to that predicted by Raoult's law. According to Raoult's law, the vapor pressure of a component in an ideal solution is directly proportional to its mole fraction in the solution. If the data follows this linear relationship, the solution is ideal.
To test this, we can plot the vapor pressure (y-axis) against the mole fraction of water (x-axis). If the data points fall along a straight line, the solution is ideal. Let's plot the data to determine if it is ideal:
```
Mole Fraction (XH2O) | Vapor Pressure (torr)
------------------------------------------------
0 | 74.0
0.15 | 77.3
0.37 | 80.2
0.54 | 81.6
0.69 | 80.6
0.83 | 78.2
1.00 | 71.9
```
By plotting these points on a graph, we can determine if they fall along a straight line. If they do, the solution is ideal.
b.) To predict the sign of ΔHsoln (delta H soln) for water-propanol solutions, we need to consider the intermolecular forces between water and propanol molecules. If the interactions between water and propanol molecules are stronger than the interactions within each pure substance, the solvation process is exothermic (ΔHsoln < 0). On the other hand, if the interactions are weaker than the interactions within each pure substance, the solvation process is endothermic (ΔHsoln > 0).
To predict the sign of ΔHsoln, we need to determine the nature of the interactions between water and propanol molecules.
c.) Based on the nature of the interactions between propanol and water molecules, we can determine if they are weaker than, stronger than, or equal to the interactions between the pure substances.
d.) The lowest normal boiling point corresponds to the solution with the highest vapor pressure. By examining the provided data, we can determine which solution has the highest vapor pressure.
pH2O = XH2O*PoH2O
Calculate each point and compare the result of the calculation with the experimental details.