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Chapter 11: Problem 21

When pure methanol is mixed with water, the resulting solution feels warm. Would you expect this solution to be ideal? Explain.

Short Answer

Expert verified
The methanol-water solution is not considered an ideal solution because its enthalpy of mixing is not zero, as indicated by the solution feeling warm. This means the interactions between the methanol and water molecules are different from their interactions with themselves, which deviates from the properties of an ideal solution as described by Raoult's Law.

Step by step solution

01

Understand the properties of an ideal solution

An ideal solution follows Raoult's Law, which states that the partial vapor pressure of each component in a solution is proportionate to the mole fraction of that component. Ideal solutions possess two essential properties: 1. The interactions between the solute and the solvent are similar to those between the solute and itself. 2. The enthalpy of mixing (螖H_mix), which is the heat change when two or more compounds are mixed, is equal to zero.
02

Examine the given information about the methanol-water solution

The information provided is that when pure methanol is mixed with water, the resulting solution feels warm. This indicates that the mixture is releasing heat as the solution forms, so the enthalpy of mixing (螖H_mix) is not zero; it is negative. In exothermic processes (where heat is released), the enthalpy of mixing has a negative value.
03

Compare the properties of the methanol-water solution to the properties of an ideal solution

We know that for a solution to be considered ideal, the enthalpy of mixing should be zero. However, for the methanol-water solution, the enthalpy of mixing is negative (since the solution feels warm). This difference in enthalpy values indicates that the interactions between the methanol and water molecules are not the same as the interactions between methanol and itself or water and itself.
04

Draw the conclusion

Since the enthalpy of mixing for the methanol-water solution is not zero, and the interactions between the solute and the solvent are different from the interactions between the solute or solvent with themselves, we can conclude that the methanol-water solution is not an ideal solution.

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Most popular questions from this chapter

Formic acid \(\left(\mathrm{HCO}_{2} \mathrm{H}\right)\) is a monoprotic acid that ionizes only partially in aqueous solutions. A \(0.10 M\) formic acid solution is \(4.2 \%\) ionized. Assuming that the molarity and molality of the solution are the same, calculate the freezing point and the boiling point of \(0.10 M\) formic acid.

Pentane \(\left(\mathrm{C}_{5} \mathrm{H}_{12}\right)\) and hexane \(\left(\mathrm{C}_{6} \mathrm{H}_{14}\right)\) form an ideal solution. At \(25^{\circ} \mathrm{C}\) the vapor pressures of pentane and hexane are 511 and 150\. torr, respectively. A solution is prepared by mixing 25 mL pentane (density, \(0.63 \mathrm{~g} / \mathrm{mL}\) ) with \(45 \mathrm{~mL}\) hexane (density, \(0.66 \mathrm{~g} / \mathrm{mL})\) a. What is the vapor pressure of the resulting solution? b. What is the composition by mole fraction of pentane in the vapor that is in equilibrium with this solution?

Calculate the molarity and mole fraction of acetone in a \(1.00 \mathrm{~m}\) solution of acetone \(\left(\mathrm{CH}_{3} \mathrm{COCH}_{3}\right)\) in ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right) .\) (Density of acetone \(=0.788 \mathrm{~g} / \mathrm{cm}^{3} ;\) density of ethanol \(\left.=0.789 \mathrm{~g} / \mathrm{cm}^{3} .\right)\) Assume that the volumes of acetone and ethanol add.

A solution of sodium chloride in water has a vapor pressure of \(19.6\) torr at \(25^{\circ} \mathrm{C}\). What is the mole fraction of solute particles in this solution? What would be the vapor pressure of this solution at \(45^{\circ} \mathrm{C} ?\) The vapor pressure of pure water is \(23.8\) torr at \(25^{\circ} \mathrm{C}\) and \(71.9\) torr at \(45^{\circ} \mathrm{C}\) and assume sodium chloride exists as \(\mathrm{Na}^{+}\) and \(\mathrm{Cl}^{-}\) ions in solution.

How does \(\Delta H_{\text {soln }}\) relate to deviations from Raoult's law? Explain.
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