Titration: A Quantitative Chemical Analysis

• Titration, or titrimetry, is a quantitative chemical analysis technique to find the unknown concentration of a reactant.
• Volumetric analysis is another term, because titration relies on volume measurements.
• A titrant (or titrator), which is a reagent with a known concentration (standard solution) and volume, reacts with an analyte (or titrand) of unknown concentration.
• A calibrated burette or chemistry pipetting syringe adds the titrant, to precisely measure the consumed amount when the endpoint is reached.
• The endpoint signals titration completion, determined via an indicator.
• The endpoint should match the equivalence point, where the titrant's moles equal the analyte's moles, or a multiple in polyprotic acids.
• In strong acid-strong base titrations, the endpoint has a pH of around 7, indicated by a lasting color change like phenolphthalein turning pink.

Moles Calculations

• Molarity x Liters = Moles
• Molarity x Milliliters = Millimoles

Endpoint indication

• Visual indicators are commonly used, where the reactant mixture changes color at the endpoint.
• Acid-base titrations use pH indicators like phenolphthalein (turns pink above pH 8.2) or methyl orange (red in acids, yellow in alkali).
• Redox titrations with KMnO4 (purple) do not need an indicator; the solution turns colorless when the titrant is reduced.
• The equivalence point is marked by a faint, lasting pink color from excess permanganate.

Sample Preparation

• Both titrant and analyte must be in liquid form, achieved by dissolving solid samples and diluting concentrated ones.
• Buffering maintains a specific pH, by adding buffer solutions to the reactant solution.
• Masking involves "masking" certain ions to prevent unwanted reactions, by adding a solution that weakly binds or forms a solid with the ion.
• Some redox reactions need heating to increase reaction rate.

Solution Properties

• A solution is a homogenous mixture of two or more substances (a solute and a solvent).
• Electrolytic property (Conduction because of ionization; electrolyte and non-electrolyte)
• Ionic compounds in water (Ionization)
• Molecular compounds in water (Do not ionize)
• Strong and Weak Electrolytes (complete and incomplete ionization)

Expressing Concentrations of Solution

• Molarity (M) is a common concentration measurement, defined as moles of solute per liter of solution.
• Molarity = Moles of solute / Liters of solution
• Moles of solute = Weight of solute / Molecular weight of solute

Dilution

• Dilution lowers concentration by adding solvent, keeping the solute's moles constant.
• M1V1=M2V2

Redox Titration

• Redox titrations involve oxidation-reduction reactions, with electron transfer between reacting ions in aqueous solutions.

Permanganate Titrations

• Use potassium permanganate as an oxidizing agent in acidic media (using dilute sulfuric acid).
• Potassium permanganate acts as a self-indicator.
• Before the endpoint, the solution is colorless; after the equivalence point, one extra drop of KMnO4 imparts a pink color.
• Used for estimating ferrous salts, oxalic acid, oxalates, hydrogen peroxide, etc.
• Potassium permanganate solution is standardized before use.

Dichromate Titrations

• Use potassium dichromate as an oxidizing agent in acidic media (using dilute sulfuric acid).
• Potassium dichromate solution can be directly used for titrations.
• Mainly used for estimating ferrous salts and iodides.
• In titrations of K2Cr2O7 versus ferrous salt, use an external indicator (potassium ferricyanide) or an internal indicator (diphenyl amine).

Iodimetric and Iodometric Titrations

• Involve the reduction of free iodine to iodide ions and the oxidation of iodide ions to free iodine.

Iodimetric Titration

• Uses free iodine, dissolved in potassium iodide solution due to iodine's volatility and low water solubility.

Iodometric Titrations

• An oxidation agent reacts with excess potassium iodide in neutral or acidic media to release free iodine.