Acid-Base Titrations 14.3

Calculations involving neutralization reactions

Learning Objectives

• Understand the neutralization reaction … strong acid and base reaction

• Concept of titration, end point, and equivalence point and how they relate to neutralization reaction

• How to solve titration problems … how to determine unknown acid or base concentration

Neutralization Reaction• Acid + Base Salt + Water

–Called a neutralization reaction–Is a double replacement reaction–Requires use of an indicator to

identify neutralization point• Strong acid + Strong base = neutral

solution–If # of H+ = # of OH-

Titration

• A titration is a reaction where a solution of known concentration (standard solution) is used to identify a solution of unknown concentration

Practical Examples of Titrations

• Determining blood glucose levels.• Determination of medical proportions

in a IV drip. • Amount of salt and sugar in food.• Level of acidity in wine and cheese.• Level of acidity in fresh water

samples.

End Point• The end point of a titration is

when the solution just barely changes color

• The equivalence point is the point where the acid and base exactly react with one another

• Ideally, the end point should be the same as the equivalence point

Titration CalculationIn a titration, 27.4 ml of a 0.0154 M HCl solution is added to 20.0 mL sample of NaOH solution of unknown concentration. What is the molarity of the basic solution?

HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)SA SB Neutralization

First we need to figure moles of HCl used to neutralize NaOH in reaction.

0.0274 L x 0.0154 mol/L = 4.22 x 10-4 mol of HCl

Titration Calculation

HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq)

= 4.22 x 10-4 mol of HCl

= 4.22 x 10-4 mol of NaOH

M of NaOH = 4.22 x 10-4 mol of NaOH .0200 L

M of NaOH = .021 M

Titration EndpointHow can you tell when you have added enough NaOH?

Titration Curve

Titration Calculation Shortcut

• Objective: to find the M of the unknown acid or base.

• Use a balanced chemical equation to determine the mole/mole ratio of acid to base.

MaVana=MbVbnb

• M = molarity• V = volume• n = # of H3O+ ions in the acid or OH- ions in the base. (if there are

no OH- ions in the base, n = 1)

Weak Acid-Strong BaseHC2H3O2(aq) + NaOH(aq) H2O(l) + C2H3O2

- (aq)

WA SB CB

HC2H3O2(aq) + OH-(aq) C2H3O2- (aq)

WA SB CB

Only basic salt is left when we reach equivalence point, therefore the final pH of solution must be basic.

Strong Acid-Weak BaseH3O+(aq) + NH3(aq) H2O(l) + NH4

+(aq)SA WB CA

H+(aq) + NH3(aq) NH4+(aq)

SA WB CA

Only acidic salt is left when we reach equivalence point, therefore the final pH of solution must be acidic.

Note: For strong acid and strong base titration, pH should be close to 7 at equivalence point.

Cool Down

• How many moles of sulfuric acid are required to completely neutralize 0.50 mol of sodium hydroxide?

• How many ml of 0.56 M potassium hydroxide are needed to completely neutralize 150.0 ml of a 1.56 M of phosphoric acid?