Acid-Base Titrations and Curves

Acid-Base Titrations

• Titration is a technique used to determine the concentration of an unknown solution (analyte) by reacting it with a solution of known concentration (titrant).
• Neutralization reactions are common in acid-base titrations.
• Acidimetry involves the quantitative determination of basic drugs.
• Alkalimetry involves the quantitative determination of acidic drugs.
• Strong acids and bases completely dissociate in water.
• The stoichiometric ratio of the acid-base reaction needs to be known.
  • Example: HCl + NaOH → HOH + Na⁺ + Cl⁻, the stoichiometric ratio is 1:1.
• Equilibrium needs to be considered, like Kw = [H₃O⁺][OH⁻] = 10⁻¹⁴

Titration Curves for Strong Acids and Bases

• The pH before titration begins can be calculated using the given concentration of the analyte.
• pH calculation before equivalence point can be calculated by knowing the concentrations of the acid and base, along with the volumes of those substances. 
  • Example: [H₃O⁺] = ((Cacid Vacid - Cbase Vbase)/(Vacid + Vbase) * consider acid volume in litres, and the base volume in litres, and their respective concentrations in Moles/Litres
• pH at equivalence point is determined by the autodissociation of water.
  • Example: Kw = [H3O⁺] [OH⁻) = 10⁻¹⁴ which leads to pH = 7.0000 (4s.f.)

Titration Curves for Weak Acids and Bases

• Differences in titration curves of weak acid/base solution vs strong acid/base solution:
  • The end point break in the weak acid/base titration curves are smaller than that of strong acid/base titration curves.
  • The selection of indicator is critical in weak acid/base titration than strong acid/base titration
• The midpoint on the titration curve of a weak acid/base occurs at pH = pKa.
• The equivalence point pH changes depending on if the substance being titrated is an acid or base
  • If a weak acid is titrated, a buffer region exists before the equivalence point. If a weak base is titrated, a buffer region will also exist before the equivalence point.

Polyfunctional Acids/Bases

• Polyfunctional acids have multiple ionizable protons (e.g., H₃PO₄).
• Polyfunctional bases have multiple ionizable hydroxide ions (e.g., ethylenediamine).
• Separate equivalence points are observed in the titration curves if the ratios of successive dissociation constants are greater than approximately 10⁴ .
• Equivalence points can be observed in the titration curves for dissociation steps where Kₐ is greater than approximately 10⁻⁸.

Acid-Base Color Indicators

• Indicators are organic weak acids or bases that change colour over a specific pH range.
• The indicator's colour change from acid form to conjugate base form is distinct.
• The indicator's ratio of concentrations of the acid form to conjugate base form (HIn/In⁻) determines the solution's colour.
• pH = pKa ± 1, the indicator changes colour between pH = pKa - 1 and pKa + 1.

Amino Acids

• Amino acids are polyprotic, containing both a carboxyl group and an amino group.
• The isoelectric point (pI) is the pH at which an amino acid or the ion of an amino acid has zero net charge.
• Titration of amino acids reveals multiple equivalence points due to their multiple ionizable protons.

Direct Titration Methods

• Direct titration methods are used for analyzing substances using standard solutions.

Indirect Titration Methods

• Indirect titration methods, also known as residual or back titrations, determine the concentration of substances by reacting with a known excess of a standard solution, then titrating the remaining unreacted excess.

Additional Notes

• There are different types of titrations (e.g., strong acid/strong base, weak acid/strong base, strong base/weak acid, weak base/strong acid etc.). Different titrations give different titration curves. There can be graphs, tables, equations etc. that go along with specific titrations.
• Titration curves can be used to determine equivalence points, select indicators, determine pH at equivalence points etc.

Explore the concepts of acid-base titrations and the calculation of pH in various scenarios. This quiz covers neutralization reactions, stoichiometric ratios, and titration curves for strong acids and bases. Test your understanding of these essential chemistry principles.