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 - = H 2 O 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 formula M acid x V acid = M base x V base

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 Rx B. calculate V acid = 50 ml V base = 25 ml M base = 0.5 M M acid =M base x V base = 0.5 M x 25 ml = 0.25 M V acid 50 ml

Multiprotic Acids/Bases Acids/Bases that release more than one H+/OH- Example: Ca(OH) 2 is a diprotic base aq Dissociation: Ca(OH) 2 Ca OH- 1 mole of Ca(OH) 2 releases 2 moles of OH- Formula changes to : M acid V acid = 2 M base V base

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 M acid x V acid = 2 M base x V base V acid = 50 ml V base = 25 ml M base = 0.5 M M acid = 2 x M base x V base = 2 x 0.5 M x 25 ml = 0.5 M V acid 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: M acid x V acid = 3 M base x V base V acid = 150 ml V base = 38 ml M base = 2 M M acid =3 M base x V base = 3x 2 M x 38 ml = 1.52 M V acid 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 : H 2 SO 4 New Formula: 2M acid x V acid = 3M base x V base V acid = 150 ml V base = 38 ml M base = 2 M M acid =3 M base x V base = 3x 2 M x 38 ml = 0.76 M V acid 2 x 150 ml