Question

For each of the following five reactions, circle the specific chemical species that is: reduced, and draw a box around the specific chemical species that is oxidized:

a) MnO₂ (s) + 2 I^- (aq) +4 H⁺ (aq) --> Mn²⁺ (aq) + I₂ (aq) + 2 H₂O (l)
b) Cd (s) + 2 NiO(OH) (s) + 2 H₂O (l) --> 2 Ni(OH)₂ (s) + Cd(OH)₂ (s)
c) NH₄⁺ (aq) + 2 O₂ (g) --> NO₃^- (aq) + 2 H⁺ (aq) + H₂O (l)
d) 2 CuFeS₂ (s) + 4 O₂ (g) --> Cu₂S (s) + 2 FeO (s) + 3 SO₂ (g)
e) 2 K₂FeO₄ (aq) + 3 Zn (s) --> Fe₂O₃ (s) + ZnO (s) + 2 K₂ZnO₂ (aq)

Answer 1

Very confusing text. It could be about:

      -    species = elements and their oxidation states

• species = substances that are reduced forms and oxidised forms
• reactants that will be reduced or oxidised
• products that were reduced or oxidised

I solve for the first interpretation. To avoid any confusion I add the oxidation states (of the involved elements).

Bold : oxidised forms

Italic : reduced formed

a)     MnO₂ (s) + 2 I^- (aq) +4 H⁺ (aq) --> Mn²⁺ (aq) + I₂ (aq) + 2 H₂O (l)

4+ 1- 2+               0

b) Cd (s) + 2 NiO(OH) (s) + 2 H₂O (l) --> 2 Ni(OH)₂ (s) + Cd(OH)₂ (s)

0 3+ 2+ 2+

c) NH₄⁺ (aq) + 2 O₂ (g) --> NO₃^- (aq) + 2 H⁺ (aq) + H₂O (l)

3-                0              5+ 2-

d) 2 CuFeS₂ (s) + 4 O₂ (g) --> Cu₂S (s) + 2 FeO (s) + 3 SO₂ (g)

       2+      2-             0 1+ 2- 4+2-

e) 2 K₂FeO₄ (aq) + 3 Zn (s) --> Fe₂O₃ (s) + ZnO (s) + 2 K₂ZnO₂ (aq)

                 6+                   0 3+ 2+ 2+