The Foundations of Chemistry

 5 0 
 2 
 2

8 n

888888 888n

888888

8888888888888888888888888

8888888888

0 
 1 
 3 0

H
(aq)
NO 3 (aq)
Cu(s)88nCu^2 
(aq)
NO(g)
H 2 O(
)

We see that copper is oxidized; it is the reducing agent. Nitrate ions are reduced; they are the

oxidizing agent.

H

NO 3 
Cu88nCu^2 

NO
H 2 O


 2

 3

We make the totalincrease and decrease in oxidation numbers equal.

Oxidation Numbers Change/Atom Equalizing Changes Gives

Cu 0 88nCu
 2 
23(
2)
 6

N
 5 88nN
 2 32(3) 6

Now we balance the redox partof the reaction.

H

 2NO 3  
 3Cu 88n 3Cu^2 
 
 2NO 
H 2 O

There are 6 O on the left in NO 3 ions. A coefficient of 4 before H 2 O balances O and gives

8 H on the right. So we need 8 H
ions on the left to balance the net ionic equation.

8H
(aq)
2NO 3 (aq)
3Cu(s)88n3Cu^2 
(aq)
2NO(g)
4H 2 O(
)

This solution contains excess HNO 3 , so NO 3 is the only anion present in significant concen-

tration. Therefore, we add six more NO 3 ions to each side to give the total ionic equation.

8[H
(aq)
NO 3 (aq)]
3Cu(s)88n3[Cu^2 
(aq)
2NO 3 (aq)]
2NO(g)
4H 2 O(
)

Now we can write the balanced formula unit equation.

8HNO 3 (aq)
3Cu(s)88n3Cu(NO 3 ) 2 (aq)
2NO(g)
4H 2 O(
)

You should now work Exercise 52.

EXAMPLE 11-20 Balancing Redox Equations (CON method)

Drano drain cleaner is solid sodium hydroxide that contains some aluminum chips. When

Drano is added to water, the NaOH dissolves rapidly with the evolution of a lot of heat. The

Al reduces H 2 O in the basic solution to produce [Al(OH) 4 ]ions and H 2 gas, which gives the

bubbling action. Write the balanced net ionic and formula unit equations for this reaction.

Plan

We are given formulas for reactants and products. Recall that NaOH is a strong soluble base

(OHand H 2 O can be added to either side as needed). We apply our five-step procedure.

Solution

We write the unbalanced net ionic equation and assign oxidation numbers.

OH(aq)
Al(s)
H 2 O(
)88n[Al(OH) 4 ](aq)
H 2 (g)

Copper is cleaned by dipping it into
nitric acid.

422 CHAPTER 11: Reactions in Aqueous Solutions II: Calculations

 1 
 5  2 0 
 2 
 2  2 
 1  2

The Drano reaction.