1. Acid/Base Titration Buffers

2. Buffers
A mixture composed of a weak acid and its conjugate base (acidic buffer) OR weak base and its conjugate acid (basic buffer)
Allow small amounts of acids and bases into a solution without a huge change in the solution’s pH
Buffer capacity—trait of buffers indicating how much strong acid/base can be tolerated before a solution’s pH changes drastically.
Mixture allows both a weak acid and weak base to be present in solution—maintains pH
-so if strong acid added, the acid reacts with the weak conjugate base in an acidic buffer
-if a strong base added, the base reacts with the weak acid in an acidic buffer –keeps H+ and OH- ions from increasing to a point (only small amounts)
-concentrations of weak acid and CB > amt. of base or acid added to maintain pH

3. Why are buffers important to us?
Buffers present in our body keep fluids within a certain pH range.
Blood has a pH range of approximately
A buffer involving H2CO3/HCO3- maintains the blood pH
This pair is carbonic acid/hydrogen carbonate ion
Buffers help keep fluids in our body at a certain pH range—buffers present in our body
-Increase blood pH—alkalosis (base)
-Decrease blood pH--acidosis

4. Titration
Used to determine UNKNOWN concentrations of solutions through a solution of KNOWN concentration.
An acidic or basic solution of KNOWN concentration is added to an acidic/basic solution of UNKNOWN concentration.
Indicators such as phenolphtalein display a change when all of the acid or base has been neutralized.
Several types—we are focusing on acid/base titration
Change is usually color.
At neutralization, equal number of base and acid is present so don’t want to keep pouring because you will turn it into a basic solutionm.

5. To the right is the titration using an indicator.

6. Titration Terminology
End Point: point in a titration where a change is observed due to indicator.
Equivalence Point: point in a titration where enough base or acid is present to neutralize the acidic or basic solution.
We can plot a titration on a graph—titration curve
End point—color change with indicator
Want to use indicators where end point and equivalence points are roughly the same. Why? So we can tell when neutralization has happened and stop adding base.
Some indicators (phenolphtalein) do not change color right at equivalence point—so stop titration when a pink color persists for 10 seconds

7. Show points on graph and how titration proceeds.
Have students draw graphs. **Maybe**

10. Calculations MaVa = MbVb Where M is the molarity & V is the volume
Used to determine final concentration vs original concentration.
Solve like you would dilution problems.

11. Example 1:
If 20.0ml of M aqueous HCl is required to neutralize 30.0ml of an aqueous solution of NaOH, determine the molarity of the NaOH solution.
Work out problem on Elmo.
If we know the acid concentration and the amount of base we have—we can calculate the base’s concentration
-pour acid into solution until equivalence point and then read buret to tell how much base was needed (amt in volume) to neutralize base. **describe titration**
6.67 x 10-3 M NaOH

12. Example 2
A 15.5 ml sample of 0.215M KOH solution required 21.2ml of aqueous acetic acid solution in a titration experiment. Calculate the molarity of the acetic acid (CH3COOH) solution.
Work out problem on Elmo
0.157M CH3COOH

13. Example 3:
If ml of a solution of Ba(OH)2 requires ml of a 2.303M solution of HNO3 for complete titration, what is the molarity of the Ba(OH)2 solution?
M Ba(OH)2

14. Homework
Titration Problem Set # 1