Unit 11: Solutions and Colloids
How a dissolved solute quietly changes a solvent's vapor pressure, boiling point, freezing point, and osmotic pull, no matter what the solute actually is.
9 topics · 32 questions
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11.1 The Solution Process and Like Dissolves Like
- How it worksHow do solute-solvent interactions have to compete with, and win against, solute-solute and solvent-solvent interactions for a solution to form?
- How it worksWalk me through why water dissolves salt by surrounding each ion with a shell of oriented water molecules.
- Common mistakeWhy isn't 'like dissolves like' just about polarity matching, rather than the full balance of all three interactions?
- Going furtherWhat happens to salt's ability to dissolve when you swap the solvent from water to a nonpolar liquid like hexane?
Your turn1 of 2
"Like dissolves like" is often shortened to mean simply matching polar solutes with polar solvents. Why isn't that the full picture of what actually decides whether a solution forms?11.1 Enthalpy of Solution
- How it worksHow does the enthalpy of solution weigh the energy cost of separating solute and solvent particles against the energy released when they attract?
- Worked exampleFind whether dissolving ammonium nitrate is endothermic or exothermic given a lattice energy of 692 kJ/mol and a hydration energy of negative 656 kJ/mol.
- Common mistakeWhy isn't a substance dissolving always an exothermic process?
Your turn1 of 2
Find the enthalpy of solution when a solute has a lattice energy of 748 kJ/mol (energy required to separate the solid into ions) and a hydration energy of -528 kJ/mol (energy released as the ions are surrounded by solvent).11.2 Henry's Law and Gas Solubility
- How it worksHow does Henry's law tie a gas's solubility in a liquid directly to the partial pressure of that gas above the surface?
- Worked exampleFind the solubility of CO2 in soda at 4.0 atm given a Henry's law constant of 3.4 times 10−2 mol per L per atm.
- Common mistakeWhy doesn't a gas's solubility in water follow the same temperature trend that a solid's solubility usually does?
- Going furtherWhat happens to nitrogen gas dissolved in a scuba diver's blood as they ascend and the surrounding pressure drops?
Your turn1 of 2
Find the solubility of CO2 in soda at 7 atm given a Henry's law constant of 3.4 times 10−2 mol per L per atm.11.3 Raoult's Law and Vapor Pressure Lowering
- How it worksHow does Raoult's law explain vapor pressure lowering as solute particles simply taking up space at the liquid's surface?
- Worked exampleFind the vapor pressure of a solution made from 1.00 mol of glucose dissolved in 9.00 mol of water, given pure water's vapor pressure of 23.8 mmHg.
- Common mistakeWhy isn't vapor pressure lowering caused by any special attraction between the solute and the solvent?
Your turn1 of 2
Find the vapor pressure of a solution made from 3.63 mol of glucose dissolved in 15 mol of water, given pure water's vapor pressure of 23.8 mmHg.11.3 Boiling Point Elevation
- How it worksHow does lowering a solution's vapor pressure force it to be heated past 100 degrees C before it can boil?
- Worked exampleFind the boiling point of a solution made by dissolving 1.00 mol of a nonvolatile solute in 1.00 kg of water, given Kb for water of 0.512 degrees C per molal.
- Common mistakeWhy doesn't the identity of the solute, only the number of dissolved particles, decide how much the boiling point rises?
- Ties togetherHow does boiling point elevation connect back to the same vapor pressure lowering that also explains why a solution's freezing point drops?
Your turn1 of 2
Find the boiling point of a solution made by dissolving 3.63 mol of a nonvolatile solute in 2.12 kg of water, given Kb for water of 0.512 degrees C per molal.11.3 Freezing Point Depression
- How it worksHow does a dissolved solute disrupt the orderly crystal lattice a solvent needs to freeze, pushing the freezing point lower?
- Worked exampleFind the freezing point of a solution made by dissolving 2.00 mol of ethylene glycol in 1.00 kg of water, given Kf for water of 1.86 degrees C per molal.
- Common mistakeWhy can't you use freezing point depression to find a solute's molar mass without first knowing whether it's an electrolyte?
Your turn1 of 2
Find the freezing point of a solution made by dissolving 3.63 mol of ethylene glycol in 2.12 kg of water, given Kf for water of 1.86 degrees C per molal.11.3 Osmotic Pressure
- How it worksHow does a semipermeable membrane let solvent flow toward the more concentrated solution until pressure builds up and stops it?
- Worked exampleFind the osmotic pressure of a 0.100 M solution of glucose at 298 K.
- Common mistakeWhy isn't osmotic pressure the same as ordinary hydrostatic pressure pushing on a container's walls?
- Going furtherWhat happens to red blood cells placed in a hypertonic solution with a higher solute concentration than the cell's interior?
Your turn1 of 2
Find the osmotic pressure of a 0.354 M solution of glucose at 306 K (R = 0.0821 L times atm per mol per K).11.3 Colligative Properties of Electrolyte Solutions and the van't Hoff Factor
- How it worksHow does the van't Hoff factor account for an ionic compound splitting into multiple particles the instant it dissolves?
- Worked exampleFind the expected freezing point depression of a 0.100 m solution of CaCl2 in water, accounting for its van't Hoff factor.
- Common mistakeWhy doesn't the van't Hoff factor for an electrolyte always match the number of ions its formula suggests exactly?
Your turn1 of 2
Find the expected freezing point depression of a 0.363 molal solution of a salt that dissociates into 3 ions per formula unit in water (Kf for water = 1.86 degrees C per molal).11.4 Colloids and the Tyndall Effect
- How it worksHow do colloid particles stay suspended indefinitely instead of settling out the way a true suspension's larger particles would?
- How it worksWalk me through how the Tyndall effect uses scattered light to tell a colloid apart from a true solution.
- Common mistakeWhy isn't a colloid the same thing as a suspension, even though both can look cloudy?
- Going furtherWhat happens to a colloid like milk once an electrolyte is added and its particles suddenly clump together and settle out?
Your turn1 of 2
Both milk (a colloid) and muddy water left to settle (a suspension) can look cloudy at first glance. Why isn't a colloid the same thing as a suspension?