Chemistry Reference
In-Depth Information
2.
[-1]—According to Rule #5, when a halogen such as chlorine appears in a
compound, it shows an oxidation number of -1.
3.
[+1]—According to Rule #2, the oxidation number shown by an alkali
metal in a compound is +1.
4.
[-2]—Rule #6 states that oxygen shows an oxidation number of -2 in all
compounds except peroxides. Water is not a peroxide.
5.
[+2]—Rule #4 states that the alkaline earth metals, such as calcium, show
an oxidation number of +2 in all compounds.
6.
[+6]—Remember that the net charge on the compound must be equal to
zero. Oxygen shows an oxidation number of -2, and there are 4 atoms of
oxygen for a total of 4(-2) = -8. Barium is an alkaline earth metal with an
oxidation number of +2, according to Rule #4. Because there is only one
barium atom, we get a total of 1(+2) = +2. After we add the +2 from the
barium atom and the -8 from the oxygen atoms, we get +2 + (-8) = -6.
Because the one sulfur atom is the only atom left, it must be +6 to balance
the rest of the atoms.
7.
[+4]—There are two atoms of lithium, for a total charge of 2(+1) = +2.
The total charge of the oxygen is 3(-2) = -6. These two elements leave a net
charge of +2 + (-6) = -4, so the sulfur must be +4 to balance this out.
8.
[+4]—The calcium from column 2 has an oxidation number of +2. There
are three atoms of oxygen for a total charge of 3(-2) = -6. These elements
leave us with a net charge of +2 + (-6) = -4, so the carbon must be +4 to
balance this out.
Lesson 5-2 Review
1.
[LiOH]—Lithium is an alkali metal with only one valence electron, so it has
an oxidation number of +1. The hydroxide ion (OH-) has an oxidation
number of -1, so the two ions combine in a 1:1 ratio because +1 + -1 = 0.
2.
[BaSO
4
]—Barium is an alkaline earth metal with two valence electrons and
an oxidation number of +2. The sulfate ion (SO
4
2-
) has an oxidation number
of -2. The ions combine in a 1:1 ratio because +2 + -2 = 0.
3.
[AgNO
3
]—Silver has an oxidation number of +1. The nitrate ion (NO
3
-
) has
an oxidation number of -1. The ions combine in a 1:1 ratio because
+1 + -1 = 0.
4.
[NH
4
NO
2
]—This compound contains two polyatomic ions. The ammonium
ion (NH
4
+
) has an oxidation number of +1. The nitrite ion (NO
2
-
) has an
oxidation number of -1. The ions combine in a 1:1 ratio because
+1 + -1 = 0.
