Chemistry 30

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1. Balance the following redox reactions using the oxidation number method.

a. SnCl₂ + HgCl₂ → SnCl₄ + HgCl

				balance for electrons
	initial		final	change		Coefficient		Total e-
Sn		→			×		=
Hg		→			×		=
Answer:

b. HNO₃ + H₂S → NO + S + H₂O

				balance for electrons
	initial		final	change		Coefficient		Total e-
N		→			×		=
S		→			×		=
Answer:

c. NaClO + H₂S → NaCl + H₂SO₄

				balance for electrons
	initial		final	change		Coefficient		Total e-
Cl		→			×		=
S		→			×		=
Answer:

d. CdS + I₂ + HCl → CdCl₂ + HI + S

Because one of the atoms undergoing oxidation or reduction has a subscript (I₂) we will account for the number of atoms of each element when preparing our summary chart:

balance for electrons

initial

final

change

no. atoms

No. e -

Coefficient

Total e-

S

→

×

=

I

→

×

(in I2)

=

×

=

Answer:

e. I₂ + HNO₃ → HIO₃ + NO₂ + H₂O

Once again, because one of the atoms undergoing oxidation or reduction has a subscript (I₂) we will account for the number of atoms of each element when preparing our summary chart:

balance for electrons

initial

final

change

no. atoms

No. e -

Coefficient

Total e -

I

→

×

(in I2)

×

=

N

→

=

×

=

Answer:

f. MnO₄^- + H⁺ + Cl^- → Mn²⁺ + Cl₂ + H₂O

Make your own summary chart

2. Balance the following half-reactions for both atoms and electrons by adding the appropriate number of electrons to the correct side of the equation. Also identify each as either an oxidation or reduction.

		Add electrons to the equation	Oxidation or Reduction?
a.	Pb2+ → Pb
b.	Cl2 → Cl-
c.	Fe3+ → Fe2+
d.	N2O + H2O → NO + H+

3. Break each equation into two half-reactions. Identify each half-reaction as oxidation or reduction.

a.	Cu + 2 H+ → Cu2+ + H2
		oxidation
		reduction
b.	2 Al + 3 S → Al2S3
		oxidation
		reduction

4. Balance the following equations using the half-reaction method.

a. Na + Br₂ → NaBr

Step 1	Step 2	Step 3
Write the two balanced half-reactions, removing any spectator ions:	Balance for electrons	Add the half-reactions, replacing any spectator ions that were removed and/or recombining compounds
add together:
reform compound:

b. Zn + S → ZnS

Step 1	Step 2	Step 3
Write the two balanced half-reactions, removing any spectator ions:	Balance for electrons	Add the half-reactions, replacing any spectator ions that were removed and/or recombining compounds
added together:
reform compound:

c. Ag + Cr₂O₇^2- + H⁺ → Ag⁺ + Cr³⁺ + H₂O

For each half-reaction, remember to balance for atoms first, then add electrons to balance for charge.

Step 1	Step 2	Step 3
Write the two balanced half-reactions, removing any spectator ions:	Balance electrons	Add the half-reactions, replacing any spectator ions that were removed and/or recombining compounds
added together:
reform compound:

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