titration lab technique commonly utilized to determine an unknown concentration of a chemical...
TRANSCRIPT
Acid-Base Titrations
Titration
Lab technique commonly utilized to determine an UNKNOWN concentration of a chemical compound with a KNOWN concentration of another chemical compound.
Chemical compounds combine with exact stoichiometric proportions
Analyte— Chemical compound with unknown concentration
Titrant— Chemical compound with known concentration Measured with volume and concentration Added to chemical compound with unknown concentration
in titration
Acid-Base Titration
Technique used to perform a neutralization reaction
Acid/Base with KNOWN concentration used to determine acid/base with UNKNOWN concentration
Neutralization Reaction: Acid + Base Salt + H2O
Titration Terminology
End Point: point in a titration where a color change is observed
due to indicator.
Equivalence Point: point during a titration when neutralization has
occurred. Equal amount of acid and base Cannot usually be observed
We can plot a titration on a graph—titration curve
**Ideally, equivalence point = endpoint **
2 Types of Acid-Base Titrations
1) Strong Acid/Strong Base Titrations
2) Weak Acid/Strong Base Titrations
1. Strong Acid/Strong Base Titrations
Low initial pH value
Sharp increase in pH before equivalence point
Equivalence point is pH = 7
Rapid pH increase after equivalence point
**Indicators with pH range 4-10 helpful for these titrations
**Neutralization reactions
Strong Acid with Strong Base Titrant
Strong Base with Strong Acid Titrant
Example 1: Strong Acid/Strong Base Titration
Calculations
30 ml of 0.50M HCl is titrated with 0.50M NaOH.
a) Find the pH of 0.50M HCl
Example 1: Strong Acid/Strong Base Titration
Calculations
30 ml of 0.50M HCl is titrated with 0.50M NaOH.
b) Find the pH after 15 ml of NaOH added
Example 1: Strong Acid/Strong Base Titration
Calculations
30 ml of 0.50M HCl is titrated with 0.50M NaOH.
c) Find the pH after 30 ml of NaOH added
Example 1: Strong Acid/Strong Base Titration
Calculations
30 ml of 0.50M HCl is titrated with 0.50M NaOH.
d) Find the pH after 45 ml of titrant added
2. Weak Acid/Strong Base Titrations
High initial pH value
pH = pKa at half-neutralization [weak acid] = [conjugate base]
Ka = [H3O+] [A -] SO Ka = [A-]/[HA] is 1:1
[HA]
Ka = [H3O+], SO pH = pKa
2. Weak Acid/Strong Base Titrations
Equivalence point > 7 on pH scale
**Indicators with pH range > 7 helpful as pH equivalence point is basic
Example 1: Weak Acid/Strong Base Titration Calculations
30 ml of 0.5M HC2H3O2 titrated with 0.50M NaOH. Ka for acetic acid is 1.8x10 -5.
a) Find the initial pH of 0.5M acetic acid.
HC2H3O2 + OH- C2H3O2- + H2O (titration
view)
HC2H3O2 H+ + C2H3O2- (in detail)
Example 1: Weak Acid/Strong Base Titration Calculations
b) Find the pH after 15ml of NaOH were added
pH = pKa + log [C2H3O2-] / [HC2H3O2]
-used when dealing with buffer solutions
-buffer—mixture of weak acid/conjugate base
-more on this concept later
Example 1: Weak Acid/Strong Base Titration Calculations
c) Find the pH at the equivalence point.
C2H3O2- + H2O HC2H3O2 + OH-
Example 1: Weak Acid/Strong Base Titration Calculations
c) Find the pH after 40ml of NaOH are added to 30ml of 0.50M HC2H3O2.
Homework
Titration Worksheet