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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