Acid-Base Titration

Finding the amount of Acetyl Salicylic Acid in three different doses of

Aspirin

Objective

• Measuring the amount of acid (Acetyl Salicylic Acid) by neutralizing it with base

Procedure

• Adding measured amounts of a prepared base solution to an acid solution

• Neutralization Reaction• H+ + OH- = H2O• Continuously checking pH • Stop when pH= 7 is reached• Equivalence point

Equivalence Point

• pH titration curve

Dye to indicate Equivalence point

Procedure and Equipment

• Acid Base Titration

Calculating Acid/Base Titration Problems

• Use modified dilution formulaMacid x Vacid = Mbase x Vbase

P1: A 50 ml sample of HCl is neutralized by 25 ml of 0.5 M NaOH. What is the concentration of the HCl?

A. write the neutralization RxB. calculate

Vacid = 50 ml

Vbase = 25 ml

Mbase = 0.5 M

Macid =Mbase x Vbase = 0.5 M x 25 ml = 0.25 M

Vacid 50 ml

Multiprotic Acids/Bases

Acids/Bases that release more than one H+/OH-Example: Ca(OH)2 is a diprotic base

aqDissociation: Ca(OH)2 Ca2+ + 2OH-

1 mole of Ca(OH)2 releases 2 moles of OH-

Formula changes to : MacidVacid = 2 MbaseVbase

P2: A 50 ml sample of HCl is neutralized by 25 ml of 0.5 M Ca(OH)2. What is the

concentration of the HCl?Ca(OH)2 new formula Macid x Vacid = 2 Mbase x Vbase

Vacid = 50 ml

Vbase = 25 ml

Mbase = 0.5 M

Macid = 2 x Mbase x Vbase = 2 x 0.5 M x 25 ml = 0.5 M Vacid 50 ml

P3: If 38 ml of 2 M Aluminum hydroxide is used to titrate 150 ml of Hydrochloric Acid, what is the molarity of the acid?

• Al(OH)3 aluminum hydroxide : triprotic base

• New formula: Macid x Vacid = 3 Mbase x Vbase

Vacid = 150 ml

Vbase = 38 ml

Mbase = 2 M

Macid =3 Mbase x Vbase = 3x 2 M x 38 ml = 1.52 M

Vacid 150 ml

P4: If 38 ml of 2 M Aluminum hydroxide is used to titrate 150 ml of Sulfuric Acid, what

is the molarity of the acid?

Sulfuric Acid : H2SO4

New Formula: 2Macid x Vacid = 3Mbase x Vbase

Vacid = 150 ml

Vbase = 38 ml

Mbase = 2 M

Macid =3 Mbase x Vbase = 3x 2 M x 38 ml = 0.76 M

Vacid 2 x 150 ml