14. Solutions

Solutions: Solubility and Intermolecular Forces Concept 1

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Solutions: Solubility and Intermolecular Forces Example 1

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Solutions: Solubility and Intermolecular Forces Concept 2

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Solutions: Solubility and Intermolecular Forces Example 2

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Indicate the most important type of intermolecular attraction responsible for solvation in the following solution:

Methanol, CH₃OH, dissolved in ethanol, CH₃CH₂OH

Which of the following solutes will most readily dissolve in H₂O?

Two pure chemical substance are likely to mix and form a solution if:

Which of the following statements is/are true?

I. The hydrocarbon methane (CH₄) will dissolve completely in acetone (CH₃COCH₃).

II. Ammonia (NH₃) will form a heterogeneous mixture with carbon tetrachloride (CCl₄).

III. Pentane (C₅H₁₂) will form a homogeneous mixture with carbon tetrabromide (CBr₄).

IV. Methanethiol (CH₃SH) is miscible in fluoromethane (CH₃F).

The formation of a solution depends on:

Which of the following solvents would you expect to dissolve aspirin?

Which of the following is false about entropy?

According to Hess's law which of the following terms for the formation of a solution is always exothermic?

Consider a solution that is saturated with a gas and a solid at room temperature. Which of the following will occur when the solution is heated by 50°C?

When lithium chloride dissolves in water, the temperature of the solution increases. Which diagram represents the enthalpy changes of the steps in the solution-making process? (LO 13.2)

This figure shows the interaction of a cation with surrounding water molecules. (b) Which of the following explanations accounts for the fact that the ion–solvent interaction is greater for Li+ than for K+? a. Li+ is of lower mass than K+. b. The ionization energy of Li is higher than that for K. c. Li+ has a smaller ionic radius than K+. d. Li has a lower density than K. e. Li reacts with water more slowly than K. [Section 13.1]

In which solvent does sodium acetate 1CH COONa2 have the highest solubility (a) Acetone CH3OCH3 (b) Methanol (CH3OH) (c) Ethanol (CH3CH2OH) (d) Pentane (CH3CH2CH2CH2CH3)

Consider two ionic solids, both composed of singly charged ions, that have different lattice energies. (b) If not, which solid will be more soluble in water, the one with the larger lattice energy or the one with the smaller lattice energy? Assume that solute–solvent interactions are the same for both solids. [Section 13.1]

Which diagram best represents a liquid–liquid emulsion such as milk? The colored balls represent different liquid molecules. [Section 13.6]

Indicate the type of solute–solvent interaction (Section 11.2) that should be most important in each of the following solutions: (d) HCl in acetonitrile 1CH3CN2

Indicate the type of solute–solvent interaction (Section 11.2) that should be most important in each of the following solutions: (c) KBr in water

Indicate the type of solute–solvent interaction (Section 11.2) that should be most important in each of the following solutions: (b) methanol 1CH3OH2 in water

Indicate the type of solute–solvent interaction (Section 11.2) that should be most important in each of the following solutions: (a) CCl4 in benzene

Indicate the principal type of solute–solvent interaction in each of the following solutions and rank the solutions from weakest to strongest solute–solvent interaction: (c) methanol 1CH3OH2 in water

Indicate the principal type of solute–solvent interaction in each of the following solutions and rank the solutions from weakest to strongest solute–solvent interaction: (b) CH2Cl2 in benzene 1C6H62

Indicate the principal type of solute–solvent interaction in each of the following solutions and rank the solutions from weakest to strongest solute–solvent interaction: (a) KCl in water

An ionic compound has a very negative ∆Hsoln in water (b) Which term would you expect to be the largest negative number: ∆Hsolvent, ∆Hsolute, or ∆Hmix

When ammonium chloride dissolves in water, the solution becomes colder. (b) Why does the solution form?

When ammonium chloride dissolves in water, the solution becomes colder. (a) Is the solution process exothermic or endothermic?

Two nonpolar organic liquids, hexane 1C6H142 and heptane 1C7H162, are mixed. (b) Hexane and heptane are miscible with each other in all proportions. In making a solution of them, is the entropy of the system increased, decreased, or close to zero, compared to the separate pure liquids?

Two nonpolar organic liquids, hexane 1C6H142 and heptane 1C7H162, are mixed (b) Hexane and heptane are miscible with each other in all proportions. In making a solution of them, is the entropy of the system increased, decreased, or close to zero, compared to the separate pure liquids?

Two nonpolar organic liquids, hexane 1C6H142 and heptane 1C7H162, are mixed. (a) Do you expect ∆Hsoln to be a large positive number, a large negative number, or close to zero? Explain.

KBr is relatively soluble in water, yet its enthalpy of solution is + 19.8 kJ/mol. Which of the following statements provides the best explanation for this behavior? (a) Potassium salts are always soluble in water. (b) The entropy of mixing must be unfavorable. (c) The enthalpy of mixing must be small compared to the enthalpies for breaking up water–water interactions and K–Br ionic interactions. (d) KBr has a high molar mass compared to other salts like NaCl.

Oil and water are immiscible. Which is the most likely reason? (a) Oil molecules are denser than water. (b) Oil molecules are composed mostly of carbon and hydrogen. (c) Oil molecules have higher molar masses than water. (d) Oil molecules have higher vapor pressures than water. (e) Oil molecules have higher boiling points than water.

Pick an appropriate solvent from Table 13.3 to dissolve each substance. State the kind of intermolecular forces that would occur between the solute and solvent in each case. b. sodium chloride (ionic)

Which molecule would you expect to be more soluble in water: CH3CH2CH2OH or HOCH2CH2CH2OH?

Which of the following in each pair is likely to be more soluble in hexane, C6H14:(b) benzene 1C6H62 or glycerol, CH21OH2CH1OH2CH2OH,

For each compound, would you expect greater solubility in water or in hexane? Indicate the kinds of intermolecular forces that occur between the solute and the solvent in which the molecule is most soluble. a. glucose

Which of the following in each pair is likely to be more soluble in water: (c) HCl or ethyl chloride 1CH3CH2Cl2? Explain in each case.

Which of the following in each pair is likely to be more soluble in water: (a) cyclohexane 1C6H122 or glucose 1C6H12O62,

For each compound, would you expect greater solubility in water or in hexane? Indicate the kinds of intermolecular forces that would occur between the solute and the solvent in which the molecule is most soluble. d. ethylene glycol

If a single 5-g block of NaCl is placed in water, it dissolves slowly, but if 5 g of powdered NaCl is placed in water, it dis- solves rapidly. Explain.

When lithium iodide (LiI) is dissolved in water, the solution becomes hotter. d. Why does the solution form? What drives the process?

When lithium iodide (LiI) is dissolved in water, the solution becomes hotter. c. Sketch a qualitative energy diagram similar to Figure 13.7 for the dissolution of LiI.

Indicate whether each statement is true or false: (c) The solubility of most gases in water decreases as the temperature increases because water is breaking its hydrogen bonding to the gas molecules as the temperature is raised.

When lithium iodide (LiI) is dissolved in water, the solution becomes hotter. b. What can you conclude about the relative magnitudes of the lattice energy of lithium iodide and its heat of hydration?

When lithium iodide (LiI) is dissolved in water, the solution becomes hotter. a. Is the dissolution of lithium iodide endothermic or exothermic?

Which would you expect to have the larger hydration energy, SO42- or ClO4-? Explain.

Classify the strongest type of intermolecular force in the follow- ing interactions: solvent–solvent, solvent–solute, and solute– solute when solid iodine 1I22 is placed in the water. Based on these interactions, predict whether I2 is soluble in water.

Determine whether each pair of compounds forms a homogeneous solution when combined. For those that form homogeneous solutions, indicate the type of forces that are involved. d. CH3CH2OH and H2O

Determine whether each pair of compounds forms a homogeneous solution when combined. For those that form homogeneous solutions, indicate the type of forces that are involved. a. CCl4 and H2O

Predict whether the solubility of butane, C4H10, is greater in water or benzene, C6H6.

Arrange the following compounds in order of their expected increasing solubility in water: Br2, KBr, toluene (C7H8, a constituent of gasoline).

Look at the solubility graph in Figure 13.7, and estimate which member of each of the following pairs has the higher molar solubility at the given temperature. (b) CH3CO2Na or glucose at 20 °C

Water is a good solvent for many substances. What is the molecular basis for this property, and why is it significant?

Aerosols are important components of the atmosphere. Does the presence of aerosols in the atmosphere increase or decrease the amount of sunlight that arrives at the Earth's surface, compared to an 'aerosol-free' atmosphere? Explain your reasoning.

Water does not easily remove grease from dishes or hands because grease is nonpolar and water is polar. The addition of soap to water, however, allows the grease to dissolve. Study the structure of sodium stearate (a soap) and describe how it works.

The 'free-base' form of cocaine (C17H21NO4) and its protonated hydrochloride form (C17H22ClNO4) are shown below; the free-base form can be converted to the hydrochloride form with one equivalent of HCl. For clarity, not all the carbon and hydrogen atoms are shown; each vertex represents a carbon atom with the appropriate number of hydrogen atoms so that each carbon makes four bonds to other atoms

(a) One of these forms of cocaine is relatively water-soluble: which form, the free base or the hydrochloride?

A supersaturated solution of sucrose (C12H22O11) is made by dissolving sucrose in hot water and slowly letting the solution cool to room temperature. After a long time, the excess sucrose crystallizes out of the solution. Indicate whether each of the following statements is true or false: (b) After the excess sucrose has crystallized out, the system is now unstable and is not in equilibrium.

The solubility of carbon tetrachloride (CCl4) in water at 25 °C is 1.2 g>L. The solubility of chloroform (CHCl3) at the same temperature is 10.1 g>L. Why is chloroform almost ten times more soluble in water than carbon tetrachloride?

A series of anions is shown below:

The anion on the far right is called 'BARF' by chemists, as its common abbreviation sounds similar to this word. (d) Tetrabutylammonium, (CH3CH2CH2CH2)4N + is a bulky cation. Which anion, when paired with the tetrabutylammonium cation, would lead to a salt that will be most soluble in nonpolar solvents?

Compounds like sodium stearate, called 'surfactants' in general, can form structures known as micelles in water, once the solution concentration reaches the value known as the critical micelle concentration (cmc). Micelles contain dozens to hundreds of molecules. The cmc depends on the substance, the solvent, and the temperature. (a) The turbidity (the amount of light scattering) of solutions increases dramatically at the cmc. Suggest an explanation. .

Choose the pair of substances that are most likely to form a homogeneous solution.

Open Question

Arrange these compounds by their expected solubility in hexane, c6h14.

Open Question

For each of the following molecules, would you expect greater solubility in water or in hexane?

Open Question