Humboldt State University ® Department of Chemistry

Richard A. Paselk

Chem 107

Fundamentals of Chemistry

Fall 2009

Lecture Notes: 15 September

© R. Paselk 2005
 
     
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Chemical Nomenclature, cont.

Acids

Acids are compounds which give hydrogen ions (protons) in solution. There are two common inorganic acid types in terms of nomenclature:

Special names

These compounds don't follow the rules, but have been in common use so long they keep their traditional names. Examples:

Expressing and Determining Concentration

Review Formulae, FW's, and MW's:

Recall that formula weights, atomic weights and molecular weights may all be expressed in two distinct ways:

  1. amu's/particle for a single atom, molecule or "formula unit," or
  2. they may be expressed in grams/mole for macroscopic quantities.

Recall also some important terms for describing substances:

 

Moles and Molarity

When talking about atoms, molecules, etc. we are talking about individual entities, so we need a unit of amount of substance in the sense of a counted amount. The unit of substance is the mole.

Whenever we do problems involving formulae or chemical equations, in other words ratios of particles, we need to use moles. (Chemists frequently use a special term for such expressions involving ratios: Stoichiometry. We will spend some time on this concept later [see Burns, pg 315].)

So what is a mole? It is the number of atoms in 12 grams of 12C. This turns out to be a huge number: 6.022 x 1023, which is given the name Avogadro's Number. Obviously it is a constant.

Note that when we look at the Periodic Chart the atomic masses have two meanings for chemists and for us:

For example, for the equation:

2H2 + O2 right arrow 2 H2O

We have two meanings:

2Al + 3S right arrow Al2S3

  1. Two atoms of aluminum combine with three atoms of sulfur to give one "formula unit" of aluminum sulfide; thus 2(27.0 amu) + 3(32.1 amu) = 150.3 amu, or 54 amu + 96.3 amu = 150.3 amu.
  2. Two moles of aluminum combine with three moles of sulfur to give one mole of aluminum sulfide; thus 2(27.0 g) + 3(32.1 g) = 150.3 g, or 54 g + 96.3 g = 150.3 g.

Examples

% quantities:

Masses and particles:

 

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Last modified 16 September 2009