A titration - Nichols Nickelsnicholschemistry.weebly.com/uploads/5/3/2/2/5322331/titrations_without_ph.pdf · • A titration of a 25.00 mL sample of a hydrochloric acid solution

•  A titration is a process of reacting a solution of unknown concentration with one of known concentration.

•  The titrations that we will discuss are acid-base titrations. In these cases, the titration is nothing more than a neutralization reaction.

Titration Lingo

•  The substance with the unknown concentration is called the analyte.

•  The substance with the known concentration is called the titrant or standard solution.

How do you titrate?

•  In titrations, the titrant is added incrementally to the analyte until the neutralization reaction is complete.

•  During the titration, there will be a point in which the amounts of the titrant and the analyte are stoichiometrically equivalent. This point is the titration’s equivalence point.

•  Indicators are used to help detect the equivalence point of a titration.

•  Indicators change colors depending upon the acidic/basic environment of the solution.

Indicators

•  Indicators will change colors in different ranges. •  We use particular indicators for specific types of

titrations. For example, for weak acid-strong base titrations, phenolphthalein is used.

•  Phenolphthalein changes from colorless (in acidic solutions) to pink (in basic solutions).

•  The indicator’s color change should coincide with the titration’s equivalence point. This color change will signal the end point of the titration.

•  The end point of a titration signifies the complete conversion of the acid to a base or vice versa.

How do solve a problem like a titration?

•  There are various strategies, but this strategy is the most direct.

•  n[moles of acid] = n[moles of base]

•  n = moles from balanced equation (mole ratio)

•  M = moles/L

Practice Calculation #1

•  A titration of a 25.00 mL sample of a hydrochloric acid solution of unknown molarity reaches the equivalence point when 38.28 mL of 0.4370 M NaOH solution is added. What is the molarity of the HCl solution?

•  HCl + NaOH → NaCl + H2O

Practice Calculation #2

•  A student titrates a 20.00 mL sample of a solution of HBr with unknown molarity. The titration requires 20.05 mL of a 0.1819 M solution of NaOH. What is the molarity of the HBr solution?

•  HBr + NaOH → NaBr + H2O

Practice Calculation #3

•  A 50.00 mL sample of a sodium hydroxide solution is titrated with a 1.605 M solution of sulfuric acid. The titration requires 24.09 mL of the acid solution to reach the equivalence point. What is the molarity of the base solution?

•  H2SO4 + 2NaOH → Na2SO4 + 2H2O

Practice Calculation #4

•  Vinegar can be assayed to determine its acetic acid content. Determine the molarity of acetic acid in a 15.00 mL sample of vinegar that requires 22.70 mL of a 0.550 M solution of NaOH to reach the equivalence point.

•  CH3COOH + NaOH → CH3COONa + H2O

Practice Calculation #5

•  A 50.00 mL sample of potassium hydroxide solution is titrated with a 0.8186 M HCl solution. The titration requires 27.87 mL of the HCl solution to reach the equivalence point. What is the molarity of the KOH solution?

•  HCl + KOH → KCl + H2O

Sample Calculation #6

•  A 15.00 mL sample of acetic acid is titrated with 34.13 mL of 0.9940 M NaOH. Determine the molarity of the acetic acid.

•  CH3COOH + NaOH → CH3COONa + H2O

Sample Calculation #7

•  A flask contains 41.04 mL of a solution of potassium hydroxide. The solution is titrated and reaches the equivalence point when 21.65 mL of a 0.6515 M solution of HNO3 is added. Calculate the molarity of the base solution.

•  KOH + HNO3 → KNO3 + H2O