Chemistry Reference
In-Depth Information
15. [B. Mg(OH)
2
]—Magnesium has an oxidation number of +2, and the
hydroxide has an oxidation number of -1, so they combine in a 1:2 ratio. We
use parentheses around the hydroxide ion to indicate that the subscript acts
as a multiplier for both the oxygen and the hydrogen.
16. [B. BaCl
2
]—Barium has an oxidation number of +2 and chloride has an
oxidation number of -1. They combine in a 1:2 ratio, and we don't use
parentheses for monatomic ions.
17. [D. CH
2
]—Divide each subscript by 4.
18. [D. 20]—Each formula unit contains (2 x 2) = 4 atoms of oxygen, so 5
formula units must contain 5 x 4, or 20 oxygen atoms.
19. [D. C
3
H
8
]—The total mass of the carbon atoms (3 x 12.0 u) = 36.0 u and
the total of the hydrogen atoms is (8 x 1.01 u) = 8.08 u. The total mass of
the molecule is 44.08 u.
20. [C. 111 u]—(40.1 u + 2(35.5 u)) = 111.1 u
21. [N
2
O
5
]—Nitrogen (V) has an oxidation number of +5 and oxide has an
oxidation number of -2. They will both go into the number 10 evenly. We
give nitrogen a subscript of 2 because 2(+5) = +10. We give the oxygen a
subscript of 5 because 5(-2) = -10.
22. [SrBr
2
]—Strontium, an alkaline earth metal, has an oxidation number of
+2. Bromide has an oxidation number of -1. They combine in a 1:2 ratio,
because +2 + 2(-1) = 0.
23. [MgS]—Magnesium, an alkaline earth metal, has an oxidation number of
+2. Sulfide, has an oxidation number of -2. They combine in a 1:1 ratio,
because +2 + (-2) = 0.
24. [Cu(NO
3
)
2
]—Copper (II) has an oxidation number of +2, as indicated by
the Roman numeral. Nitrate has an oxidation number of -1. They combine
in a 1:2 ratio, because +2 + 2(-1) = 0. We need parentheses because
nitrate is a polyatomic ion, and we want to indicate the need for two of
them.
25. [BaCO
3
]—Barium has an oxidation number of +2 and carbonate has an
oxidation number of -2, so they combine in a 1:1 ratio. No parentheses are
used because we only need one carbonate.
