Acid-Base Titration Experiment

• Experiment 1 focuses on Acid-Base Titration
• This experiment conducted in the Analytical Chem. 236 Lab at Kuwait University, Chemistry Department
• Objectives of the experiment are:
• Standardization of NaOH solution vs. standard KHP
• Titration of HCl vs. standard NaOH solution
• Analysis of Vinegar
• Analysis of aspirin

Acid-Base Titration

• Neutralization is a process where an acid reacts with a base to produce salt and water
• Acid + Base yields Salt + Water
• The acid–base titration process involves adding a known concentration of a base to an acid or vice versa to determine the concentration of an unknown solution
• The different types of titration:
• Acid-base titration
• Redox titration
• Precipitation titration
• Complexometric titration
• Three basic things needed for titration:
• Standard solution (Titrant): A solution of accurately known concentration
• Unknown solution (Titrand): A solution of unknown concentration
• Acid-base indicators: Weak organic acids or bases that change color based on hydrogen ion concentration
• Molarity is the number of moles of solute per liter of solution
• M = n / V, where n represents number of moles and V represents volume in liters
• The equivalence point is the point in the titration where the number of equivalents of an acid equals the number of equivalents of a base
• The endpoint is the point at which the titration process is stopped, usually indicated by a color change of an indicator

Primary Standard Solution

• Primary standard reagents must fulfill certain requirements:
• Known exact composition and purity
• Stable
• Non-hygroscopic, does not absorb CO2 from the atmosphere
• Reacts rapidly
• High molecular weight
• Phenolphthalein (ph.ph) is used as an indicator
• It is colorless in acidic medium and light pink in basic medium

Determining Solution Concentration by Titration

• Add 20.0 mL of acid solution to a flask
• Add a few drops of an acid-base indicator
• Add a standard NaOH solution from a buret
• The solution becomes basic, triggering the indicator to change color, indicating the equivalence point

Potassium Hydrogen Phthalate (KHP)

• KHP is a monoprotic, weak, very stable acid used as a primary standard
• Reaction: KHC8H4O4(aq) + NaOH(aq) -> KNaC8H4O4(aq) + H2O(l)

Chemical Equations

• NaOH + HCl -> NaCl + H2O
• NaOH + CH3COOH -> CH3COONa + H2O

Comments and Precautions

• Fill the burette with NaOH solution, removing any air bubbles from the tip.
• Add the indicator to the solution before starting the titration
• Remove air bubbles from the burette tip to prevent errors in volume reading
• Wash the burette with NaOH titrant solution to avoid diluting the titrant

Standardization of NaOH Solution Using KHP (Procedure I)

• Fill the burette with NaOH aqueous solution
• Pipette 10.00 mL of 0.10 M KHP into a 250 mL conical flask
• Add 50 mL of deionized water and 2-3 drops of phenolphthalein indicator
• Titrate against NaOH(aq) until the endpoint is reached (faint pink color)
• Record the volume of NaOH(aq) solution used
• Repeat the titration two more times

Determination of HCl Concentration Using NaOH (Procedure II)

• Pipette 10.00 mL of HCl aqueous solution into a 250 mL conical flask, then add 50 mL of distilled water and 2-3 drops of phenolphthalein indicator
• Titrate with standardized NaOH(aq) solution until a faint pink color that persists for at least 20 seconds appears
• Repeat the titration two more times and record each volume used
• Average the volumes and calculate the molarity of the unknown HCl(aq)

Analysis of Vinegar (Procedure III)

• Transfer 10.00 mL of vinegar sample to a volumetric flask and dilute to 100.00 mL
• Transfer 10.00 mL of the diluted vinegar solution to a 250 mL conical flask and add about 50 mL of distilled water
• Add 2-3 drops of phenolphthalein indicator
• Titrate against the standardized NaOH(aq) solution
• Calculate the number of moles of vinegar in the 10.00 mL diluted sample solution
• Calculate the number of moles in the original 10.00 mL vinegar sample
• Calculate the weight of vinegar in the original 10.00 mL sample and determine % (w/v), assuming the density of vinegar is 1.00 g/mL

Analysis of Aspirin (Procedure IV)

• Grind 10-20 aspirin tablets into a fine powder
• Weigh exactly 1 tablet of aspirin
• Dissolve the sample in about 30 to 50 mL of ethanol and quantitatively transfer into a 250 mL conical flask
• Add 2-3 drops of phenolphthalein indicator
• Titrate with the standardized NaOH(aq) solution from Experiment 1 until the endpoint
• Repeat the experiment
• Calculate the mass of acetylsalicylic acid in the sample, then calculate its purity [% w/w]

Standardization of NaOH using 0.10 M KHP (Calculations)

• Reaction: KHC8H4O4 (aq) + NaOH (aq) -> KNaC8H4O4 (aq) + H2O (l)
• 1 mole of NaOH reacts with 1 mole of KHP
• Moles of NaOH = moles of KHP
• MNaOH * Vaverage = MKHP * VKHP

Titration of HCl with Standard NaOH (Calculations)

• Reaction: NaOH (aq) + HCl (aq) -> NaCl (aq) + H2O (l)
• 1 mole of NaOH reacts with 1 mole of HCl
• Moles of NaOH = moles of HCl
• MNaOH * Vaverage = MHCI * VHCI

Titration with Vinegar (Calculations)

• Moles of NaOH = moles of CH3COOH
• MNaOH * Vaverage = Macetic acid * Vacetic acid
• 0.1M * burette = ? * Pipette (10 mL)
• Molarity after dilution is used to find the actual molarity before dilution: (M? x 10)before dilution = (Macetic acid x 100)after dilution
• Molesacetic acid = Macetic acid × Volacetic acid = x
• massacetic acid = molesacetic acid × molar massacetic acid = Z
• Assuming density of vinegar is 1g/mL, hence 10 mL = 10 g
• % by weight (%w/w) in 10 mL = (Z g / 10g) × 100% = x %

Titration with Aspirin (Calculations)

• Moles Aspirin = moles NaOH
• MNaOH × VNaOH
• (Mass Aspirin (g) / Molecular Wt Aspirin) x = MNaOH(partII) x VNaOH(average)
• Mass Aspirin = (0.1 moles / L) * (burette in L / 1000) * molecular weight Aspirin (180g/mol)
• % of acetyl salicylic acid in aspirin sample as tablet: (Mass A.S.A(g) / Mass tablet(g)) ×100%