Neutralization Reactions

Acid-Base Reactions• If we mix a strong acid solution with

a strong base solution

• we get a neutral solution that is neither acidic nor basic.

• For example:

• HCl + NaOH → NaCl + H2O

• H2SO4 + 2 KOH → K2SO4 + 2 H2O

Acid-Base Reactions• Mixing a strong acid with a strong

base gives us

• water

• a salt

• the conjugate base of the acid plus the conjugate acid of the base

• In this case, a salt is an ionic compound of any kind.

Acid-Base Reactions• In most cases, the net ionic

equation of a neutralization reaction is:

• H3O+ + OH- → 2 H2O

• The salt that is formed usually stays in solution.

• The salt ions are spectator ions.

Titration• Acids and bases combine in

different ratios:

• 1:1

• HCl + NaOH → NaCl + H2O

• 1:2

• H2SO4 + 2 KOH → K2SO4 + 2 H2O

• 2:1

• 2 HCl + Ca(OH)2 → CaCl2 + 2 H2O

Titration• The point where the number of mols

of hydronium ions equals the number of mols of hydroxide ions is called the equivalence point.

• The stoichiometric ratio of the acid to the base in the balanced equation tells us where the equivalence point is.

TitrationExample 1:

How many mols of sulfuric acid are required to neutralize 0.50 mols of sodium hydroxide?

nNaOH = 0.50 molH2SO4 + 2 NaOH → Na2SO4 + 2 H2O

nNaOH

nH2SO4

=21 ➙ nH2SO4 =

1×nNaOH

2 =0.50 mol

2

nH2SO4 = 0.25 mol

Titration• A titration is a neutralization

reaction under controlled conditions.

• We control the amounts of acid and base reacted while monitoring the pH of the reaction solution.

• When we reach neutralization (the equivalence point), we carefully measure the amounts of the acid and the base.

Titration• A titration uses

• a flask or beaker to hold the unknown solution

• a burette to hold the known (standardized) solution

• an indicator (added to the flask) to show the end of the titration.

Titration• The burette shows the volume

of titrant added to the flask.

• We read the meniscus to find the amount added.

• Placing a white sheet with a black section below the meniscus can help to define the meniscus.

Titration• We can use an indicator to show the

equivalence point (end point) of the titration.

• We can also use a pH meter to find the end point by generating a pH curve.

Titration• On the left, a strong base is added

to a strong acid.

• The equivalence point occurs at pH = 7.

Titration• On the right, a strong acid is added

to a strong base.

• The equivalence point also occurs at pH = 7.

TitrationExample 2:A 25-mL solution of H2SO4 is completely neutralized by 18 mL of 1.0 M NaOH. What is the concentration of the H2SO4 solution?

MNaOH = 1.0 M VNaOH = 18 mL = 0.018 LMH2SO4 = ? M VH2SO4 = 25 mL = 0.025 LH2SO4 + 2 NaOH → Na2SO4 + 2 H2O

nNaOH

nH2SO4

=21

➙nH2SO4 = nNaOH

2=

0.018 mol2

MH2SO4 = 0.36 M

nNaOH

=0.0090 mol

nH2SO4

VH2SO4=

0.0090 mol0.025 L =

= MNaOHVNaOH =(1.0)(0.018) mol =0.018 mol