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Chapter 13: Problem 13

Indicate whether each statement is true or false: (a) A solute will dissolve in a solvent if solute-solute interactions are stronger than solute-solvent interactions. (b) In making a solution, the enthalpy of mixing is always a positive number. (c) An increase in entropy favors mixing.

Short Answer

Expert verified
(a) False - A solute will dissolve in a solvent if the solute-solute interactions are weaker than the solute-solvent interactions. (b) False - The enthalpy of mixing can be both positive or negative, depending on whether the mixing is endothermic or exothermic. (c) True - An increase in entropy favors mixing, as it increases the disorder of the solute and solvent molecules.

Step by step solution

01

(a) Solute-solute vs solute-solvent interactions

A solute will dissolve in a solvent if the solute-solute interactions are weaker than the solute-solvent interactions. This is because, for a solute to dissolve in a solvent, it needs to create new interactions with the solvent, which will be stronger and more favorable than the original solute-solute interactions. Therefore, this statement is false.
02

(b) Enthalpy of mixing

The enthalpy of mixing refers to the amount of energy (heat) that is either absorbed or generated due to the mixing of two substances. The enthalpy of mixing can be a positive or a negative number, depending on whether the mixing is endothermic (energy is absorbed, a positive number) or exothermic (energy is released, a negative number). Therefore, this statement is false.
03

(c) Increase in entropy and mixing

Entropy is a measure of the degree of disorder in a system. Higher entropy indicates more randomness, while lower entropy indicates a more ordered state. An increase in entropy generally favors mixing because mixing increases the disorder of the solute and the solvent molecules. Thus, this statement is true.

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Most popular questions from this chapter

You make a solution of a nonvolatile solute with a liquid solvent. Indicate if each of the following statements is true or false. (a) The freezing point of the solution is unchanged by addition of the solvent. (b) The solid that forms as the solution freezes is nearly pure solute. (c) The freezing point of the solution is independent of the concentration of the solute. ( \(\mathbf{d}\) ) The boiling point of the solution increases in proportion to the concentration of the solute. (e) At any temperature, the vapor pressure of the solvent over the solution is lower than what it would be for the pure solvent.

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Calculate the molarity of the following aqueous solutions: (a) 0.540 \(\mathrm{g}\) of Mg \(\left(\mathrm{NO}_{3}\right)_{2}\) in 250.0 \(\mathrm{mL}\) of solution, \((\mathbf{b}) 22.4 \mathrm{gof}\) \(\mathrm{LiClO}_{4} \cdot 3 \mathrm{H}_{2} \mathrm{O}\) in 125 \(\mathrm{mL}\) of solution, \((\mathrm{c}) 25.0 \mathrm{mL}\) of 3.50 \(\mathrm{M}\) \(\mathrm{HNO}_{3}\) diluted to 0.250 \(\mathrm{L}\)

Proteins can be precipitated out of aqueous solution by the addition of an electrolyte; this process is called "salting out" the protein. (a) Do you think that all proteins would be precipitated out to the same extent by the same concentration of the same electrolyte? (b) If a protein has been salted out, are the protein-protein interactions stronger or weaker than they were before the electrolyte was added? (c) A friend of yours who is taking a biochemistry class says that salting out works because the waters of hydration that surround the protein prefer to surround the electrolyte as the electrolyte is added; therefore, the protein's hydration shell is stripped away, leading to protein precipitation. Another friend of yours in the same biochemistry class says that salting out works because the incoming ions adsorb tightly to the protein, making ion pairs on the protein surface, which end up giving the protein a zero net charge in water and therefore leading to precipitation. Discuss these two hypotheses. What kind of measurements would you need to make to distinguish between these two hypotheses?
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