Question

Is \(50 \%\) by mass of methanol dissolved in ethanol different from \(50 \%\) by mass of ethanol dissolved in methanol? Explain.

Short answer

Yes, they are different because the roles of solute and solvent are reversed.

Step-by-step solution

- Understanding the Terms

Identify that '50% by mass' means that 50 grams of the solute is dissolved in 50 grams of the solvent, making a total solution of 100 grams.

- Defining the First Case

For the first scenario, '50% by mass of methanol dissolved in ethanol', it means 50 grams of methanol (solute) is dissolved in 50 grams of ethanol (solvent). The total mass of the solution is 100 grams.

- Defining the Second Case

For the second scenario, '50% by mass of ethanol dissolved in methanol', it means 50 grams of ethanol (solute) is dissolved in 50 grams of methanol (solvent). The total mass of the solution is also 100 grams.

- Analyzing the Difference

While the total mass of the solutions in both cases is the same, the roles of solute and solvent are reversed. Mixing 50 grams of methanol in 50 grams of ethanol is chemically different from mixing 50 grams of ethanol in 50 grams of methanol because the properties of solutes and solvents can affect the solution differently.

- Conclusion

Although the mass percentages are the same, these two solutions are different due to the roles of solute and solvent being reversed.

Key concepts

Mass Percentage

Mass percentage is a crucial concept in solution chemistry. It describes the amount of a particular solute in a solvent, expressed as a percentage of the total solution mass.
For example, if you have a solution that is '50% by mass' methanol in ethanol, this means out of the total solution, 50% of the mass is made up of methanol.
Specifically, this translates to 50 grams of methanol dissolved in 50 grams of ethanol, making the total solution mass 100 grams.
To calculate mass percentage, you can use the formula: \[ \text{Mass \, \, Percentage} = \left(\frac{\text{mass \ of \ solute}}{\text{total \ mass \ of \ solution}}\right) \times 100 \] This formula helps you understand the concentration of the solute in any given solution. Remember, while mass percentages help to quantify concentrations, they don't give information on the chemical interactions within the solution.

Solute-Solvent Roles

Understanding the roles of solute and solvent is key to grasping solution chemistry.
A solute is the substance that gets dissolved, and the solvent is the substance that does the dissolving.
In our exercise, methanol and ethanol can both act as solute or solvent depending on the setup. When discussing '50% by mass of methanol dissolved in ethanol', methanol is the solute, and ethanol is the solvent.
Conversely, for '50% by mass of ethanol dissolved in methanol', ethanol becomes the solute, and methanol is the solvent.
Even though both setups have the same mass percentages, the interchange of solute and solvent roles can result in different solution properties.
The interactions between the molecules will differ, leading to variations in things like solution viscosity, boiling points, and other chemical properties.

Chemical Properties of Solutions

The chemical properties of solutions are directly influenced by the types of solute and solvent involved.
These properties include boiling and freezing points, viscosity, and reactivity.
When we switch the solute and solvent roles, as in our exercise, these properties can change significantly.
Methanol and ethanol are different in terms of molecular structure and interaction characteristics.
Thus, 50 grams of methanol dissolved in 50 grams of ethanol will not behave the same way as 50 grams of ethanol dissolved in 50 grams of methanol.
The intermolecular forces like hydrogen bonding, and dipole-dipole interactions, can vary, affecting how the solution behaves.
Understanding these differences is important for practical applications, such as formulating solutions in laboratories or industrial processes.