mole of a hydrogen molecule H 2 equals 2 g. Water has one oxygen atom.
Therefore, multiply 1 ×16 g. One mole of oxygen is 16 g.- Sum the atomic mass of atoms that make up the molecule to determine one
mole of the molecule. For water this is 2 g ++16 g =18 g. One mole of
water equals the atomic mass of 18 g. - The weight of one mole is the atomic mass of a molecule expressed in
grams. Therefore, one mole of water weighs 18 grams. - A liter of water has a mass of 1,000 grams. Calculate the number of moles
per liter by dividing the number of grams (1,000) by one mole of water (18
grams). The result is 55 moles/liter.
An Unlikely Pair: Inorganic and Organic
Chemical compounds are divided into two general categories of substances.
These are:
- Inorganic compound. A compound that does not contain the chemical ele-
ment carbon (C). - Organic compound. A compound containing carbon atoms, the exception
is carbon dioxide (CO 2 ). Carbon dioxide is inorganic. - Inorganic compounds are further divided into three categories. These are:
- Acids. An acid is any compound that dissociates into one or more hydro-
gen ions (H+) and one or more negative ions (called anions) and is a pro-
ton donor. - Bases. A base is any compound that dissociates into one or more positive
ions (called cations) and one or more negative hydroxide ions. The nega-
tive hydroxide ions (OH−) can either accept or share protons. - Salts. A salt is an ionic compound that dissociates into one or more positive
or negative ions in water, although some salts are not soluble in water. The
positive and negative ions are neither hydrogen ions nor hydroxide ions.
Sodium and chlorine atoms break away from the salt lattice when water
molecules surround them. Water molecules become oriented so that the pos-
itive poles face the negatively charged chlorine ions and the negative poles
face the positively charged sodium ions. The water’s hydrogen shells react
with the sodium and chlorine ions, drawing the ions from the salt lattice.
CHAPTER 2 Chemical Elements of Microorganisms^37