1. Neutralization Reactions
When an acid and base are both placed in the same aqueous system, they react.
These are a special type of double replacement reaction called a neutralization reaction

2. Neutralization Reactions
In a neutralization reaction, an acid and base react to make water and salt
Salt is just a name for an ionic compound
Example:
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

3. Neutralization Reactions
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
Let’s look at the ionic equation for this reaction.
Now if we look at the net ionic equation

4. Neutralization Reactions
We will ONLY look at STRONG ACID AND STRONG BASES reacting
This is because when we have equal moles of acid and base, we will have a neutral solution
A pH of 7
If you did not have a BOTH strong acids and bases, the pH when the moles are equal would not be exactly 7.
It would depend on the Ka and Kb of the acids and bases

5. Titrations
Neutralization reactions are used in a lab procedure called a Titration
In a titration, an acid and base are mixed until their moles are equal.
When they are neutralized
This can be used to find the concentration of either substance
When the moles are equal this is called the equivalency point

6. Titrations
Typically the substance with the known concentration (standard) is added to the substance with the unknown concentration
The substance being added from the burette is called the Titrant
The substance in the flask being added to is called the Analyte

7. Indicators
During a titration, the equivalency point is shown using an indicator
Indicators change colour in acidic or basic conditions
Every indicator has it’s own equilibrium that allows it to change colour

8. Indicators Indicators change colour based on their own equilibrium
In-(aq) + H+(aq) ⇌ HIn(aq)
Basic Form Acidic Form
Colour 1 Colour 2
Phenophthalein

9. Indicators
Because indicators work using equilibrium, they have a range that they will change colours over.
This means that when an indicator changes colour, it is not an EXACT pH that they do this at.
Because of this, different titrations may need different indicators.
Indicator
pH range
Colour change
methyl orange
red to yellow
litmus
red to blue
phenolphthalein
colourless to pink

10. Indicator Examples
Indicator
pH range
Colour change
methyl orange
red to yellow
litmus
red to blue
phenolphthalein
colourless to pink
Example - A given solution turns methyl orange yellow, litmus blue, and phenolphthalein pink. What is the approximate pH of the solution?
Methyl orange in yellow when pH is above 3.2 Litmus is blue when pH is above 5.8, and Phenolphthalein is pink when pH is above 8.2.
Therefore the solution would have to have a pH ___________

11. Indicators
The moment the colour changes in a titration is called the Endpoint
The moles may not be equal at the endpoint, but the colour has changed indicating that you should stop adding your substance.

12. Titration Examples
During a titration 75.8 mL of a M standard solution of HCl is titrated to end point with mL of a NaOH solution with an unknown concentration. What is the concentration of the NaOH solution?
A 20.0 mL solution of strontium hydroxide, Sr(OH)2, is placed in a flask and a drop of indicator is added. The solution turns colour after 25.0 mL of a standard M HCl solution is added. What was the original concentration of the Sr(OH)2 solution?