Mole and Molar Concentration

Chapter 3 Important Chemical Concepts: Expressing Quantities and Concetrations

I. Important Units of Measurement

A. SI Units (International System of Units)

SI Base Units

Physical Quantity Name of Unit Abbreviation

Mass kilogram kg
Length meter m
Time second s
Temperature kelvin K
Amount of substance mole mol
Electric Current ampere A
Luminous Intensity candela cd

Prefixes for Units

giga- G 109 mega- M 106 kilo- k 103 deci- d 10-1 centi- c 10-2 milli- m 10-3 micro- u 10-6 nano- n 10-9 pico- p 10-12 femto- f 10-15 atto- a 10-18

B. The mole and millimole

1. Mole – amount of a chemical species. Avogadro’s number 6.022 X 1023 of particles.

2. Millimole – 1mmol = 10-3 mol

3. Molar mass – mass in grams of one mole of a substance.

Example 3-5 page 76

4.62 g Na3PO4

Molar Mass Na3PO4 = (22.9898 gNa X 3) + (30.9738 gP) + (15.9994 gO X4) = 163.9408 g per mol Na3PO4

Moles Na3PO4 = 4.62 g X 163.9408 g/ mol = 2.818 X 10-2 mol Na3PO4

Moles Na = 2.818 X 10-2 mol Na3PO4 X 3 mol Na / mol Na3PO4 = 8.45 X 10-2 mol Na

Na+ ions = 8.45 X 10-2 mol Na X (6.022 X 1023) = 5.08 X 1022 ions

C. Solutions and Their Concentrations

1. Molar Concentration or Molarity – Number of moles of solute in one Liter of solution or millimoles solute per milliliter of solution.

2. Analytical Molarity – Total number of moles of a solute, regardless of chemical state, in one liter of solution. It specifies a recipe for solution preparation.

3. Equilibrium Molarity – (Species Molarity) – The molar concentration of a particular species in a solution at equilibrium.

4. Percent Concentration

a. weight percent (w/w) = weight solute X 100% weight solution

b. volume percent (v/v) = volume solute X 100% volume solution

c. weight/volume percent (w/v) = weight