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
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