1. Volumetric Analysis: Titration
An introduction

2. The Big Picture
Use a solution of known concentration (the standard solution) to determine the concentration of an unknown solution

3. What we need The chemical equation
A way to measure amounts of solution added
Fixed and variable
A way to determine that the titration is complete
Reaction should be fast

4. NaOH(aq) + H2SO4(aq)  Na2SO4(aq) + H2O(l)
The Chemical Reaction
Must know the equation and correct stoichiometric ratios
Example:
Write the equation for the titration of sulfuric acid with sodium hydroxide
NaOH(aq) + H2SO4(aq)  Na2SO4(aq) + H2O(l) 2 2
Not balanced
Therefore the base to acid ratio is 2:1

5. Volume Measurements
Titrate a variable amount of solution into a known volume of solution until titration is complete
Fixed (known) volume should be measured with high precision:
Use pipette (p.17)
Variable volume should be as high precision as possible: Use burette

6. How to determine titration is complete
Usually an indicator is used
Terms
End point: when indicator changes color
Equivalence point: when a stoichio-metrically equivalent amount of titrant has been added to solution

7. Phenolphthalein is a very common acid-base indicator
More on indicators
Phenolphthalein is a very common acid-base indicator
Colorless in acid
Pink in base

8. Example
25.00 mL of M sulfuric acid is titrated with NaOH, requiring mL to reach the endpoint. What is the NaOH concentration?

9. 2 NaOH(aq) + H2SO4(aq)  Na2SO4(aq) + 2 H2O(l)
Example
We place mL of acid and a couple drops of the indicator into the flask and titrate with base until the solution turns slightly pink.
2 NaOH(aq) + H2SO4(aq)  Na2SO4(aq) + 2 H2O(l)

10. Example
25.00 mL of M sulfuric acid is titrated with NaOH, requiring mL to reach the endpoint. What is the NaOH concentration?

11. Example
Moles of acid
Moles of base
Concentration of base

12. Some Titration Techniques
Start with burette at or beyond 0.00 mL
It doesn’t matter, just record it!
Don’t waste time getting exactly 0.00 mL
Titrate to the ½ drop
Add extra water if needed
How does this affect calculations?

13. Some Titration Techniques
Stir!
Place on white paper
Palest and most reproducible pink possible

14. Common Abbreviations for Acetic Acid
CH3COOH
HCH3CO2
C2H4O2
C2H3O2H
HOAc

15. This Week’s Analysis
Goal: Determine molar concentration and mass percentage acetic acid in vinegar
Units of concentration of acetic acid in vinegar:
Units on mass % of acetic acid in vinegar:

16. This Week’s Analysis Oxalic acid as a primary standard
Why?
One oxalic acid solution per 2 groups
Note that oxalic acid is a hydrate
How does this affect you?
10 mL pipettes
250 mL volumetric flasks

17. Procedure Proposal
How you will prepare your oxalic acid solution (~0.25 M)
How you will determine NaOH concentration including calculations and chemical reactions
How you will determine the concentration of the acetic acid in vinegar (and how many trials)
Road map of calculations for calculating C and mass % acetic acid from your data
Don’t even think of using C1V1=C2V2

18. This investigation, Author
3: Introduction and Conclusion
1: Discussion
2: Data/Results and Experimental
A: Introduction, Conclusion, Data/Results
B: Discussion and Experimental