NEUTRALIZATION REACTIONS
When an acid reacts with a base, a double displacement reaction occurs. This is called a neutralization reaction.
HCl(aq) +
Acid
+
NaOH(aq)
Base


NaCl(aq)
Salt
+
+
H2O(l)
water
When any strong acid reacts with any strong base in the mole ratio from the balanced chemical equation, a neutral
aqueous solution of a salt is formed.
For most neutralization reactions, there are no visible signs that a reaction is occurring (slight exothermic), so an
acid-base indicator is used. This is a substance that changes colour in acidic and basic solutions. Most acid-base
indicators are weak, monoprotic acids. The weak acid is one colour, its conjugate base is a different colour.
H (indicator)(aq)  H+ + (indicator)-(aq)
Colour 1
Colour 2
In an acidic solution, the indicator does not dissociate very much, and appears as colour 1. In a basic solution, the
indicator dissociates much more, appearing as colour 2. Often, a single drop of indicator causes a dramatic change
in colour.
Scientists can determine the concentration of one solution in a neutralization reaction, just by knowing the
concentration of the other solution.
Example: 13.84 mL of HCl(aq) just neutralizes 25.00 mL of a 0.1000 mol/L solution of NaOH(aq). What is the
concentration of the HCl(aq)?
Given:
VHCl
= _________ mL
VNaOH = _________ mL
[NaOH]= _________ mol/L
Step 1: Balanced Equation  HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
Step 2: Amount (in mol) = [ ] (in mol/L) x Volume (in L)
Amount NaOH
= _________ mol/L x ________ L
= _______ mol
Step 3: HCl reacts with NaOH in a 1:1 ratio, so there must be ________ mol HCl
Step 4: [ ] (in mol/L) = Amount (in mol)
Volume (in L)
= ____________mol
L
= ________ mol / L