What is titration?
Titration is a widely employed analytical technique utilized for the quantification of analytes in solution.
Type of titration procedures
- Acid-Base Titrations
- Strong Acid-Strong Base Titrations
- Weak Acid-Weak Base Titrations
- Strong Acid-Weak Base Titration
- Weak Acid–Weak Base Titration
- Redox Titrations
- Precipitation Titrations
- Complexometric Titrations
Acid-Base Titrations
The concentration of an acid or a base in a solution can be found using quantitative analytical techniques called acid-base titrations. This technique involves the gradual addition of a titrant to a sample solution until the reaction reaches its equivalence point, where the amounts of acid and base are stoichiometrically equal. The acid-base reaction is tracked using a pH indicator to determine its progress.
HA(Acid) + BOH(Base) 🡪 BA(Salt) + H2O
Example :
NaOH(aq) + HCl(aq) 🡪 NaCl(aq) + H2O
- Acid-base indictors
| Indicator | PKIN | Color Change |
| Methyl Orange | 3.5 | Red – Orange |
| Bromocresol Green | 4.7 | Yellow – Blue |
| Litmus | 6.5 | Red – Blue |
| Bromothymol Blue | 7.1 | Yellow – Blue |
| Phenol Red | 7.8 | Yellow – Red |
| Phenolphthalein | 9.4 | Colorless – Pink |
- Application of Acid-Base Titration
- Used to find the concentration of an unknown acid or base in a solution, which is essential in both educational and research laboratories.
- Ensures the correct pH levels in products like fruit juices, vinegar, and soft drinks.
- Validates the concentration of active ingredients in drugs.
- Measures the acidity or alkalinity of water samples.
- Ensures that cosmetic products are within the appropriate pH range.
- Key terms
- Titrant: The known-concentration solution that is added to the analyte in the titration process.
- Analyte: The substance whose concentration is being determined.
- Equivalence Point: The point in the titration at which the titrant’s concentration equals the analyte’s concentration in the solution stoichiometrically.
- End Point: The moment at which the titration is finished and the indicator changes color.
- Indicator: A substance that changes color at the equivalence point.
- Standard Solution: A solution of known concentration used in the titration.
- Molarity (M): A measurement of a solution’s concentration given in moles of solute per liter of solution.
- Neutralization: A process that frequently happens during acid-base titrations in which an acid and a base react chemically to generate water and salt.
- Buffer: A solution that resists changes in pH, sometimes used in titrations to maintain a constant pH environment.
Strong Acid-Strong Base Titrations
A strong acid-strong base titration is a common laboratory procedure used to determine the concentration of an acid or base.
Strong bases and acids are totally dissociated, meaning that every acid or base molecule will split into its constituent ions. Equivalency between H+ and OH– ions causes H2O to develop at the equivalence point, where pH 7.0 is reached. For this titration, the pH at the equivalence point will always be 7.0.
Thermodynamic Feasibility
H+(aq) + OH–(aq) 🡪 H2O(l)
The titration is feasible because ∆G0 value is lower than -40 kJ/mol
Plotting the titration curve
Titration of 25.00 cm3 of 0.10 M HCl with 0.10 M NaOH
- Initial pH
At the initial point there are no any OH– ions present in the solution; Only H+ ions remain.
Concentration of the HCl = 0.10 M
- 12.50 cm3 of NaOH was added to the solution
A volume of 12.50 cm3 of NaOH reacted with 12.50 cm3 of H+, leaving 12.50 cm3 of unreacted H+ remaining.
- One drop of NaOH was added just before reaching the end point (24.95 cm3)
Remaining H+ volume is 0.05 cm3
- Equivalence point pH
At the equivalence point, no acid or base molecules remain to be neutralized. The only remaining substance is H2O. Here, pH is determined by the dissociation of the water.
H2O (l) 🡪 H+(aq) + OH–(aq)
H2O (l) 🡪 H+(aq) + OH–(aq)
- An excess of one drop of NaOH was added (25.05 cm3)
An excess volume of 0.05 cm3 remains in the solution.
- 37.50 cm3 of NaOH was added to the flask
An excess volume of 12.50 cm3 remains in the solution.
