Practice Questions

Define osmosis and osmotic pressure.

Justify why aquatic life is more comfortable in cold water than in warm water, based on the principles of gas solubility.

Calculate the molarity of a solution prepared by dissolving $4.9 \text{ g}$ of sulfuric acid ($H_2SO_4$) in enough water to make $250 \text{ mL}$ of solution. The molar mass of $H_2SO_4$ is $98 \text{ g/mol}$.

A solution is prepared by dissolving 10 g of glucose ($C_6H_{12}O_6$) in 90 g of water. Recall the formula for mass percentage and find the mass percentage of glucose in the solution.

Define a solution and list its main components.

Explain the term 'mole fraction' and write its formula for a binary solution.

Recall the formula for elevation in boiling point and explain each term in the equation.

A chemist claims that molarity is a better unit for expressing concentration than molality for experiments involving significant temperature changes. Critique this claim.

Apply the concept of osmosis to explain what happens when red blood cells are placed in a hypotonic solution (e.g., pure water).

A solution contains 2 moles of ethanol and 8 moles of water. Recall the formula for mole fraction and find the mole fraction of each component.

Design a non-volatile solute that, when $30$ g of it is dissolved in $500$ g of water, will elevate the boiling point of water to exactly $100.104^{\circ}C$ at 1 atm pressure. Formulate the required molar mass of this solute. ($K_b$ for water = $0.52 \text{ K kg/mol}$).

Analyze the reason for positive deviation from Raoult's law in a solution of ethanol and cyclohexane. How does this relate to the sign of the enthalpy of mixing ($\Delta_{\text{mix}}H$)?

Examine why an azeotropic mixture of ethanol and water cannot be separated into pure components by fractional distillation.

Two volatile liquids, A and B, form an ideal solution. At $300$ K, the vapour pressures of pure A and pure B are $100$ mm Hg and $300$ mm Hg, respectively. Formulate the composition of the liquid mixture (in terms of mole fraction) that will have a total vapour pressure of $250$ mm Hg at $300$ K.

Recall Raoult's law for a solution containing a non-volatile solute.

Define an azeotrope and name the two types of azeotropes.

Define Molarity and Molality. List one key difference between them.

Recall Henry's Law.

Describe an ideal solution and state the conditions for its formation.

Explain what colligative properties are and list the four main colligative properties.

A solution of ethanol ($C_2H_5OH$) in water is $46\%$ by mass. Calculate the mole fraction of ethanol and water in the solution.

Compare molarity and molality as units of concentration, explaining which one is preferred for experiments involving temperature changes and why.

The Henry's law constant ($K_H$) for oxygen ($O_2$) dissolved in water at $298 \text{ K}$ is $4.34 \times 10^4 \text{ atm}$. If the partial pressure of oxygen in the air is $0.2 \text{ atm}$, calculate the concentration of dissolved oxygen in water.

Calculate the boiling point of an aqueous solution containing $120 \text{ g}$ of urea ($NH_2CONH_2$, molar mass $60 \text{ g/mol}$) in $500 \text{ g}$ of water. The boiling point of pure water is $100^{\circ}C$ and the molal elevation constant ($K_b$) for water is $0.52 \text{ K kg/mol}$.

Contrast ideal solutions and non-ideal solutions showing negative deviation, based on intermolecular forces and thermodynamic properties ($\Delta_{\text{mix}}H$ and $\Delta_{\text{mix}}V$).

The vapor pressure of pure water at $298 \text{ K}$ is $23.8 \text{ mm Hg}$. Calculate the vapor pressure of a solution prepared by dissolving $36 \text{ g}$ of glucose ($C_6H_{12}O_6$, molar mass $180 \text{ g/mol}$) in $162 \text{ g}$ of water (molar mass $18 \text{ g/mol}$).

An antifreeze solution is prepared by dissolving $31 \text{ g}$ of ethylene glycol ($C_2H_6O_2$, molar mass $62 \text{ g/mol}$) in $200 \text{ g}$ of water. Calculate the freezing point of the solution. ($K_f$ for water is $1.86 \text{ K kg/mol}$, freezing point of pure water is $0^{\circ}C$).

Propose a reason at the molecular level for why a mixture of chloroform ($CHCl_3$) and acetone ($CH_3COCH_3$) exhibits a negative deviation from Raoult's law. Illustrate the specific intermolecular interaction responsible for this behavior.

A scuba diver breathes compressed air at a depth of 30 meters, where the pressure is significantly higher than at the surface. Justify why the diver must ascend slowly to avoid "the bends," a painful and dangerous condition. Relate your explanation to Henry's Law and the solubility of nitrogen gas in blood.

Critique the statement: "Raoult's law is fundamentally different from Henry's law and there is no relationship between them."

For determining the molar mass of macromolecules like proteins and polymers, osmotic pressure is preferred over other colligative properties like elevation in boiling point or depression in freezing point. Evaluate this preference by comparing the magnitudes of the effects and the experimental conditions required for each method.

A coastal community is facing a severe freshwater shortage. Propose a solution based on a colligative property to make seawater potable. Describe the principle, the necessary components of the setup, and the key condition that must be met for the process to be successful.

To increase the shelf-life of a carbonated beverage, a manufacturer proposes to seal the bottles under a $CO_2$ pressure of $4.0$ atm at $25^{\circ}C$. Given that Henry's law constant ($K_H$) for $CO_2$ in water at this temperature is $1.67 \times 10^8$ Pa, calculate the molar concentration of dissolved $CO_2$ under these conditions. Evaluate if this concentration is significantly higher than the solubility at atmospheric pressure (partial pressure of $CO_2 \approx 4 \times 10^{-4}$ atm). (Note: $1 \text{ atm} = 1.013 \times 10^5 \text{ Pa}$)

Explain why scuba divers use tanks filled with air diluted with helium.

Explain the concept of abnormal molar mass and introduce the van't Hoff factor, $i$.

Analyze why dissolving benzoic acid ($C_6H_5COOH$) in benzene results in an experimentally determined molar mass that is approximately double its actual molar mass.

A pharmaceutical company needs to prepare an intravenous (IV) solution that is isotonic with blood plasma. The required concentration is $0.9\%$ mass/volume of $NaCl$. They are considering using molarity, molality, or mass percentage (w/w) for their internal quality control specifications instead. Evaluate the suitability of each of these three concentration units for this application, justifying which one would be the most reliable and why, considering factors like temperature variations during storage and transport.

Design an experiment to determine the molar mass of an unknown non-volatile, non-electrolyte solid using the principle of freezing point depression. Your design must specify the necessary apparatus, the solvent you would choose (justify your choice using data from Table 1.3), the measurements to be taken, and the formula you would use to calculate the molar mass.

Benzene ($C_6H_6$) and toluene ($C_7H_8$) form a nearly ideal solution. At $300 \text{ K}$, the vapor pressure of pure benzene is $50.71 \text{ mm Hg}$ and that of pure toluene is $32.06 \text{ mm Hg}$. Calculate the total vapor pressure of a solution made by mixing $39 \text{ g}$ of benzene and $46 \text{ g}$ of toluene. Also, find the mole fraction of benzene in the vapor phase.

A student dissolves $1.00$ g of benzoic acid ($C_6H_5COOH$, Molar Mass = $122 \text{ g/mol}$) in $50.0$ g of benzene and measures a freezing point depression of $0.853$ K. The cryoscopic constant ($K_f$) for benzene is $5.12 \text{ K kg/mol}$. Evaluate whether benzoic acid behaves as an ideal solute in benzene. Calculate the experimental molar mass and the van't Hoff factor, and propose a structural reason for your findings.

A solution is prepared by dissolving $1.8 \text{ g}$ of a polymer in $100 \text{ mL}$ of water at $300 \text{ K}$. The osmotic pressure of this solution is found to be $3.6 \times 10^{-3} \text{ bar}$. Calculate the molar mass of the polymer. (Gas constant $R = 0.083 \text{ L bar K}^{-1} \text{mol}^{-1}$)

A solution containing $0.52 \text{ g}$ of $KCl$ in $100 \text{ g}$ of water freezes at $-0.24^{\circ}C$. Calculate the van't Hoff factor ($i$) and the degree of dissociation ($\alpha$) of $KCl$. (Molar mass of $KCl = 74.5 \text{ g/mol}$, $K_f$ for water $= 1.86 \text{ K kg/mol}$).

Formulate a method to determine the degree of dissociation ($\alpha$) of a weak electrolyte like acetic acid ($CH_3COOH$) in water using freezing point depression measurements. Derive the relationship between the van't Hoff factor ($i$), the number of ions produced per formula unit ($n$), and the degree of dissociation ($\alpha$).

Create a hypothetical binary liquid solution (components A and B) that would exhibit a large positive deviation from Raoult's law and form a minimum boiling azeotrope. Describe the expected nature of intermolecular forces (A-A, B-B, and A-B), the sign of $\Delta_{mix}H$ and $\Delta_{mix}V$, and sketch the resulting vapour pressure-composition diagram.

Describe positive and negative deviations from Raoult's law in non-ideal solutions.