titration lab technique commonly utilized to determine an unknown concentration of a chemical...

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