Volumetric Analysis: Titration

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
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 21
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
More on indicators

• Phenolphthalein is a very common acid-base
  indicator
• Colorless in acid
• Pink in base

8
Example

• 25.00 mL of 0.460 M sulfuric acid is titrated
  with NaOH, requiring 28.45 mL to reach the
  endpoint. What is the NaOH concentration?

9
Example

• We place 25.00 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 0.460 M sulfuric acid is titrated
with NaOH, requiring 28.45 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 doesnt matter, just record it!
• Dont 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 Weeks 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 Weeks 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
• Dont even think of using C1V1C2V2

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