 Chemistry Honors/AP

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WebLecture: Solubility and Colligative properties

Kotz and Triechel, Chemistry and Chemical Reactivity Chapter 13: Sections 3-5.

1. 13.3 Solubility, or the amount of a specific solute that we can dissolve in a given solvent, depends upon pressure and temperature.
• Henry's Law shows that the solubility of a gas or liquid is directly proportional to gas pressure: Sg = kHPg, where k is the Henry's Law constant for the particular solute and solvent. Solubility increases if the gas pressure increases.
• Le Chatelier's principle describes how solubility changes with temperature. In general, a change in a factor determining equilibrium in a system will cause the system to adjust so that the effect of the change is counteracted. If we have an endothermic reaction (A + heat → B), and we add heat, the endothermic reaction will run forwards at an accelerated pace to reduce the amount of heat in the reactants. If we have an exothermic reaction (A → B + heat), and we had heat, the reaction will run backwards to reduce the amount of heat in the products.
2. 13.4 Colligative Properties are those properties which depend entirely on the ratio of solute particles to solvent particles.
• Raoult's Law describes the ideal behavior of the vapor pressure of a solvent in solution to the vapor pressure above a pure solvent: Psolvent = Xsolventsolvent where X is the mole fraction of the solvent in the solution. [Note that when we have a pure solution, X = 1, and the pressures are equal, as required.]
• As a result of Rauolt's law, the boiling point of a solvent will rise as it is diluted with solute, and its freezing point will drop. When ions are involved, the temperature change will be affected by a value (the van't Hoff factor, i).
• Boiling point elevation: ΔTbp = Kbpmsolute
• Freezing point depression: ΔTfp = Kfpmsolute
• Freezing point of ions: i = ΔTfp Measured/ΔTfp calculated = ΔT measured/Kfpm are a
• Osmotic pressure is the force exerted when a solution is separated by a semipermeable membrane into different concentrations. The laws of thermodynamics will drive the system to equilibrium, by forcing the solute to move from its high concentration area to the lower concentration area (diffusion), or that is not possible, by driving the solvent to move from the low concentration area to the high concentration area (osmosis). This pressure Π = cRT, where c is molarity, R is the gas constant, and T is the absolute temperature (in Kelvin). It's

Note: We can use a solute with a known K (determined experimentally under other circumstances) and measure the temperature change ΔTbp of a solution. From this data, we can solve for the molarity of the solute in the solution.

3. 13.5 Colloids or colloidal dispersions form when very large molecules can only diffuse slowly in a solvent. Such particles have high molecular masses and relatively large sizes, and they are big enough to scatter visible light, making the solutions in which they occur cloudy (Tyndall effect).
• A sol is a dispersion of a solid solute in a fluid medium (solvent).
• A gel is a dispersion that is immobile. Cooled jello is a gel.
• An emulsion is a collodial dispersion of one liquid in another, such as oil in water. a

Videos for Chapter 13: Solutions and their Behavior

Review the Videos at Thinkwell Video Lessons.

• Under "Physical Properties of Solutions"
• Effects of Temperature and Pressure on Solubility
Temperature Change and Solubility
• Extractions
• Pressure Change and Solubility
• Colligative Properties
Vapor Pressure Lowering
• Boiling Point Elevation and Freezing Point Depression
• Osmosis
• Colligative Properties of Ionic Solutions
• Colloids
Colloid Formation and Flocculation

Homework problems: See your Moodle assignment!

AP #10 GUIDED INQUIRY — Determination of solution concentration of copper sulfate solutions using visual colorimetry. — Phases II

Prepare a set of calibrated solutions, and compare transmittance, absorbance of light through the solutions as a function of concentration. Then attempt to estimate the concentration of an unknown solution by comparison with your calibrated solution.

• APGIE Lab 1: What is the Relationship Between the Concentration of a Solution and the Amount of Transmitted Light Through the Solution
• IGHCE Lab 7.5 Determine the Concentration of a Copper Sulfate Pentahydrate Solution through Visual Colorimetry
• HSCMK XIII-1: Determine Boron Concentration with Curcumin using Visual Colorimetry