General Chemistry II: Solution Chemistry Study Guide (Chapter 14)

Q1. Enumerate the three types of interactions involved in the solution process and their respective enthalpies.

Background

Topic: Solution Formation and Energetics

This question tests your understanding of the energetic changes and molecular interactions that occur when a solution forms.

Key Terms:

• Solute-solute interactions

• Solvent-solvent interactions

• Solute-solvent interactions

• Enthalpy ($\Delta H$) associated with each interaction

Step-by-Step Guidance

1. Identify the three types of interactions: solute-solute, solvent-solvent, and solute-solvent.

2. Recall that breaking solute-solute and solvent-solvent interactions requires energy (endothermic, $\Delta H > 0$).

3. Forming solute-solvent interactions releases energy (exothermic, $\Delta H < 0$).

4. Associate each interaction with its respective enthalpy change: $\Delta H_1$, $\Delta H_2$, and $\Delta H_3$.

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Q2. Write enthalpy equations for both molecular and ionic compounds and define each term in both equations. Sketch energy diagrams for exothermic and endothermic situations.

Background

Topic: Enthalpy Changes in Solution Formation

This question tests your ability to write and interpret enthalpy equations for dissolving different types of compounds and to visualize energy changes.

Key Terms and Formulas:

• $\Delta H_{solution}$: Enthalpy change for solution formation

• For molecular compounds: $\Delta H_{solution} = \Delta H_1 + \Delta H_2 + \Delta H_3$

• For ionic compounds: $\Delta H_{solution} = -U_{lattice} + \Delta H_{hydration}$

Step-by-Step Guidance

1. Write the general enthalpy equation for molecular compounds, identifying each term.

2. Write the enthalpy equation for ionic compounds, defining lattice energy and hydration enthalpy.

3. Sketch or describe energy diagrams for both exothermic ($\Delta H_{solution} < 0$) and endothermic ($\Delta H_{solution} > 0$) cases.

4. Label the axes and key points on the diagrams (energy vs. progress of solution formation).

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Q3. Distinguish between saturated, unsaturated, and supersaturated solutions. Which solution is the least stable?

Background

Topic: Types of Solutions

This question tests your understanding of solution concentration and stability.

Key Terms:

• Saturated solution

• Unsaturated solution

• Supersaturated solution

Step-by-Step Guidance

1. Define a saturated solution: contains the maximum amount of solute that can dissolve at a given temperature.

2. Define an unsaturated solution: contains less solute than the maximum possible.

3. Define a supersaturated solution: contains more solute than is normally possible at that temperature.

4. Consider which solution is least stable and why (think about tendency to precipitate).

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Q6. Define terms of Henry’s law and be able to use it to calculate the solubility of oxygen in water in ppm.

Background

Topic: Gas Solubility and Henry's Law

This question tests your ability to apply Henry's law to calculate gas solubility in water.

Key Formula:

$C = k_H P$

Where:

• $C$ = concentration of dissolved gas (mol/L or ppm)

• $k_H$ = Henry's law constant (mol/L·atm)

• $P$ = partial pressure of the gas (atm)

Step-by-Step Guidance

1. Identify the values for $k_H$ and $P$ for oxygen in water.

2. Plug these values into the Henry's law equation: $C = k_H P$.

3. Convert the concentration from mol/L to ppm if needed (1 ppm = 1 mg/L for dilute aqueous solutions).

4. Check units and make sure all conversions are correct.

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Q14. Define and be able to solve problems dealing with molarity, molality, percent by mass, mass/volume %, volume/volume, mole fraction, ppm, ppb, and ppt.

Background

Topic: Solution Concentration Units

This question tests your ability to define and use various concentration units in calculations.

Key Terms and Formulas:

• Molarity ($M$): $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

• Molality ($m$): $m = \frac{\text{moles of solute}}{\text{kg of solvent}}$

• Percent by mass: $\% = \frac{\text{mass of solute}}{\text{mass of solution}} \times 100$

• Mass/volume %: $\% = \frac{\text{mass of solute}}{\text{volume of solution}} \times 100$

• Volume/volume %: $\% = \frac{\text{volume of solute}}{\text{volume of solution}} \times 100$

• Mole fraction ($X$): $X = \frac{\text{moles of component}}{\text{total moles in solution}}$

• ppm: $\text{ppm} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 10^6$

• ppb: $\text{ppb} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 10^9$

• ppt: $\text{ppt} = \frac{\text{mass of solute}}{\text{mass of solution}} \times 10^{12}$

Step-by-Step Guidance

1. Define each concentration unit and write its formula.

2. Identify the information needed to solve for each unit (mass, volume, moles).

3. Set up sample calculations for each unit, making sure to use proper units and conversions.

4. Check your setup before proceeding to the final calculation.

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Q19. Define each term in the boiling point elevation equation and understand the usefulness of this equation. Be able to use this equation to determine the molar mass of a chemical compound.

Background

Topic: Colligative Properties – Boiling Point Elevation

This question tests your understanding of boiling point elevation and its application in determining molar mass.

Key Formula:

$\Delta T_b = i K_b m$

Where:

• $\Delta T_b$ = boiling point elevation (°C)

• $i$ = van't Hoff factor (number of particles formed)

• $K_b$ = ebullioscopic constant (°C·kg/mol)

• $m$ = molality (mol/kg)

Step-by-Step Guidance

1. Identify the values for $\Delta T_b$, $K_b$, and $i$ from the problem statement.

2. Rearrange the equation to solve for molality: $m = \frac{\Delta T_b}{i K_b}$.

3. Use the definition of molality to relate the mass of solute to moles and mass of solvent.

4. Set up the calculation to determine the molar mass, stopping before plugging in the final values.

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Q29. What is Raoult’s law? Write an equation to describe it. Define all terms of the equation.

Background

Topic: Vapor Pressure of Solutions

This question tests your understanding of Raoult's law and its application to ideal solutions.

Key Formula:

$P_{solution} = X_{solvent} P^0_{solvent}$

Where:

• $P_{solution}$ = vapor pressure of the solution

• $X_{solvent}$ = mole fraction of the solvent

• $P^0_{solvent}$ = vapor pressure of pure solvent

Step-by-Step Guidance

1. Write Raoult's law equation for a solution.

2. Define each term in the equation.

3. Explain how the vapor pressure of the solution is affected by the presence of solute.

4. Set up a sample calculation using the equation, stopping before plugging in values.

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