# Quiz | Oxidation-Reduction Reactions

1

What kind of reactions is Cu2+ (aq) + 2 e- → Cu (s) ?

Oxidation-Reduction reaction

Oxidation reaction

Reduction reaction

Galvanization reaction

Oxidation: particle becomes more positively charged (loss of electrons)
Reduction: particle becomes less positively charged (gain of electrons)
In this half reaction, Cu2+ gains 2 electrons and becomes less positively charged

2

What is an oxidation reaction?

The loss of electrons and a decrease in oxidation state

The loss of electrons and an increase in oxidation state

The gain of electrons and an increase in oxidation state

The gain of electrons and a decrease in oxidation state

Oxidation: particle becomes more positively charged (loss of electrons) ⇒ oxidation number increases

3

What is the oxidation number of the carbon atom in H2CO3?

0

+2

+4

+8

Oxidation states: Hydrogen atoms with a nonmetal: +1 and Oxygen atoms in compounds: -2

H2CO3 ⇒ 2 H+ + 3 O2- + Cx
H2CO3 is neutral: 0 = 2 (+1) + 3 (-2) + x ⇒ x = +4
Oxidation number of the carbon atom in H2CO3 = +4

4

What is the oxidation number of chromium atom in Cr2O72-?

+4

+6

+8

+12

Oxidation number of oxygen atoms in compounds: -2

Cr2O72- ⇒ 7 O2- + 2 Crx
Cr2O72- is negatively charged: -2 = 7 (-2) + 2 x ⇒ x = +6
Oxidation number of chromium atom in Cr2O72- = +6

5

What is the reducing agent in the reaction: Fe2O3 + 3 CO → 2 Fe + 3 CO2?

Fe2O3

CO

Fe

CO2

Reducing agent: substance that is oxidized in a redox reaction (electron donor). Its oxidation state increases
Oxidation state of Iron: in Fe2O3 = +3; in Fe = 0 ⇒ Fe is reduced, Fe2O3 is the oxidizing agent
Oxidation state of Carbon atom: in CO = +2; in CO2 = +4 ⇒ C is oxidized, CO is the reducing agent

6

What is the reduced species in the reaction: O2 + 6 I- + 2 H2O  2 I3- + 4 OH-?

O2

I-

H2O

OH-

The reduced species is the particle that becomes less positively charged ⇒ its oxidation state decreases
Oxidation state of oxygen atoms: in O2 = 0; in H2O = -2; in OH- = -2 ⇒ O2 is reduced