Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 107

Fundamentals of Chemistry

Fall 2009

Lecture Notes: 17 November

© R. Paselk 2005
 
     
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Returned Exam 2

Solution Concentrations-a Review & Some New Stuff.

Solutions: a solution occurs when one chemical is completely dissolved or dispersed in another. We most commonly think of solutions as being liquid, but solid solutions also occur, such as the various metal alloys like steel, brass and bronze.

In a solution the substance present in highest concentration is considered to be the solvent, while components in lesser amounts are considered to be solutes. If you dissolve a sugar cube in water you get a sugar solution, where water is the solvent, and sugar is the solute.

FYI

Example:

  • What is the solvent in 80 proof rum: 80 proof = 40% alcohol in water, so water is the solvent.
  • What is the solvent in 151 proof rum: 151 proof = 75.5% alcohol in water, so alcohol is the solvent.

 Concentration Measures

Concentration Terms

Percent Concentration

Mass percent

ppt = parts/thousand (1mg/L of water); ppb = parts/billion (1 microgram/L of water)

Volume percent

Molarity: The most commonly used concentration term in chemistry = moles of solute dissolved in 1 L of solution.

Two types of situation arise giving two kinds of problems:

Making molar solutions.

Dilution problems (see 22 September).

Molality: = moles of solute dissolved in 1 kg of solvent.

Example: What is the concentration of a solution made by dissolving 10.00 g of KI in 1.00000 kg of water?

First need to find the number of moles of KI:

(10.00 g) / ({39.10 g+ 126.9 g}/mole) = 6.135 x 10-2 mole

Thus the concentration will be 6.135 x 10-2 m

Mole fraction: = moles of solute dissolved in total moles of solution = na /Sigman

Example: What is the mole fraction of a solution of 10.0 moles of glycerol dissolved in 15.0 moles of water?

(10 mol) / (10 mol + 15 mol) = 10/25 = 0.400

Solubility

Colloids: defined by particle size = 1.0 nm< colloid < 100 nm (particles in solution are 0.1 - 1.0 nm in diameter, whereas particles > 100 nm dispersed in a fluid are considered to be in suspension.) Colloids generally do not settle out.

Colligative properties (properties which depend only on the number or concentration, not on the type, of particles). Be able to solve problems for:


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Last modified 18 November 2009