Tasks and exercises
1. Indicate the oxidation number of each of underlined atom in the
compounds below.
(a) HBr, (b) LiH, (c) CCl4, (d) CO, (e) ClO-,
(f) Cl2O7, (g) H2O2 (h)
CrO3 (i) CrO42-, (j)
Cr2O72-
2. When the equation, Al(s) + NO3-(aq)
→ NO(g) + Al3+(aq)
is balanced, the Al/NO3-
ratio is …
3. For each of the following questions, find the oxidation number of
underlined atoms. Identify
oxidants and reductants and point out the atoms whose oxidation
number changed.
a)
PbO2 + 4H+ + Sn2+ → Pb2+
+ Sn4+ + 2H2O
b)
5As2O3 + 4MnO4- + 12H+ →
5As2O5 + 4Mn2+ +
6H2O
4. In the reaction,
O2 + 4e- → 2O2-, is O2 oxidized or
reduced?
5. Balance the following redox reaction using the oxidation number
method.
Al + Cu2+ → Al3+ +
Cu
6. Balance the following redox reaction using the oxidation number
method.
copper + nitric acid
→ copper(II) nitrate +
nitrogen monoxide + water
7. In a redox reaction, MnO4- is changed to
MnO42-. How many electrons must be lost or gained by
Mn?
8. What is the oxidation number of each element in potassium dichromate
(K2Cr2O7)?
9. A solution was made by taking 2.500g of
KMnO4
and dissolving it in enough water to make 1.000 liter of solution.
This solution was used to titrate
H2C2O4·2H2O, a very pure substance.
In acidic media, the reaction is
MnO4- (aq) + H2C2O4
(aq) + … → CO2 (g) + Mn2+ (aq) +
…
How many ml of this solution are required to titrate a 0.480 g sample
of H2C2O × 2H2O? …