Lab 6 - Titration Flashcards
Titration
It isa volumetric technique in whicha solution of one reactant (titrant) isadded from the burette toa solution ofa second reactant (analyte) in conicalflask until the equivalence point/endpoint is reached, at end point thecolor of solution is changed.
Types of titration
- Redox titration
- Precipitation Titration
- Complexometry titration
- Non- aqueous titration
- Acid-base titration
Why is titration used in pharmacy?
Determining the Concentration of Active Ingredients Quality Control and Purity Testing
Drug Stability Testing
Determining Solubility and Dissolution
Assaying Complexes and Chelates
Redox reaction
reduction-oxidation reaction occurs between the titrant and the analyte. The titrant donates or accepts electrons, changing the oxidation state of the analyte
Indicator reaction
Redox indicators or changes in colour due to oxidation state shifts
Example of redox titrations
Titration of iron (II) ions (Fe²⁺) with potassium permanganate (KMnO₄) (strong oxidizing agent)
Precipitation reaction
reaction between the titrant and analyte forms an insoluble precipitate
Precipitation indicator
the appearance or disappearance of a precipitate
Precipitation example
Titration of chloride ions (Cl⁻) with silver nitrate (AgNO₃) forming AgCl (s)
Complexometry reaction
involves the formation of a complex ion between the analyte (often a metal ion) and the titrant(typically a chelating agent like EDTA)
Complexometry indicator
Metal ion indicators, which change colour when metal ions are free or bound to the complexing agent
Complexometry example
Titration of calcium ions (Ca²⁺) with EDTA (Ethylenediaminetetraacetic acid)
Non aqueous reaction
involves the titration of substances that are insoluble or poorly soluble in water. The titration is carried out in a non-aqueous solvent (such as acetic acid or ethanol)
Non aqueous indicators
Acid-base indicators
Non aqueous example
Titration of a weak acid like benzoic acid (C₆H₅COOH) in glacial acetic acid using a non-aqueous base like sodium methoxide (NaOCH₃) (strong base)
Acid - base reaction
acid and a base react to neutralize each other. The titration involves adding a titrant (either an acid or a base) to the analyte (the substance being analyzed) until the equivalence point is reached, where the number of moles of H⁺ ions from the acid equals the number of moles of OH⁻ ions from the base.
Acid-base indicator
Acid-base indicators
Acid-base example
Titration of acetic acid (CH₃COOH) with sodium hydroxide (NaOH)
Strong base, weak acid
What are the indicators?
An indicator is an organic compound that changes the colour of the solution at the endpoint/ equivalence point.
Acid-base indicators are composed of
These indicators are either weak acid or weak base.
Equivalence point
No. of moles of H+ = No.of moles of OH-
True or false
The equivalence point can be determined 100%
False
Phenolphthalein
pH range 8-10
Colourless in acidic
Basic in medium
Phenolpthalein
• Weak acid
• Acid-base indicator, pH indicator
• In a titration of acetic acid (weak acid) and sodium hydroxide (strong base), the equivalence point typically occurs at a pH around 8.7 (slightly basic).
• CH3COOH + NaOH → CH3COONa + H2O
Calculations at the equivalent point
fa x Ma x Va= fb x Mb x Vb
Number of moles of acid (H+) = number of moles of base (OH-)
fa= number of reacting H+ per formula of the acid.
fb= number of reacting OH- per formula of the base.
Stoichiometric factor, fa
It represents the number of protons (H⁺ ions) that can be donated
- Monoprotic Acids
An acid that donates only one proton (H⁺) per molecule in an aqueous solution.
* Hydrochloric acid (HCl): HCl → H⁺ + Cl⁻
* Acetic Acid (CH3COOH): CH₃COOH ⇌ CH₃COO− + H+ - Diprotic Acids
An acid that can donate two protons (H⁺) in a stepwise manner.
Sulfuric Acid (H₂SO₄):
First dissociation: H₂SO₄ → H⁺ + HSO₄⁻
Second dissociation: HSO₄⁻ → H⁺ + SO₄²⁻ - Triprotic Acids
An acid that can donate three protons.
Phosphoric acid (H₃PO₄):
First dissociation: H₃PO₄ → H⁺ + H₂PO₄⁻
Second dissociation: H₂PO₄⁻ → H⁺ + HPO₄²⁻
Third dissociation: HPO₄²⁻ → H⁺ + PO₄³⁻
Stoichiometric Factor, fb
It represents the number of protons (H⁺ ions) that are accepted or hydroxide ions (OH⁻) that can be donated
- Monobasic Bases
A base that can accept only one proton (or donate one hydroxide ion, OH⁻).
Sodium hydroxide (NaOH): NaOH → Na⁺ + OH⁻ - Dibasic Bases
A base that can accept two protons (or donate two hydroxide ions, OH⁻)
Calcium hydroxide
(Ca(OH)₂): Ca(OH)₂ → Ca²⁺ + 2OH⁻
Magnesium hydroxide
(Mg(OH)₂): Mg(OH)₂ → Mg²⁺ + 2OH⁻3.
Tribasic Bases
A base that can accept three protons (or donate three hydroxide ions, OH⁻) These bases are less common but still important in certain chemical contexts.
Aluminium hydroxide (Al(OH)₃)Al(OH)₃ → Al³⁺ + 3OH⁻
Molarity
the number of moles of solute per litre of solution
Does not consider the chemical reactivity or the number of ions produced by the solute. It is simply the amount of substance in a given volume.
Normality
the number of gram equivalents of solute per litre of solution
equivalent refers to the amount of a substance that reacts with or supplies one mole of H⁺ ions (for acids) or one mole of OH⁻ ions (for bases)
For acids:
Normality (N) = Molarity (M) × fa number of protons (H⁺) donated per molecule
For bases:
Normality (N) = Molarity (M) × fb number of hydroxide ions (OH⁻) released per molecule
For monoprotic acids and bases, molarity and normality are equal
Why do we dilute?
it doesn’t affect the outcome of the titration in terms of the concentration of acetic acid being analyzed.
- Dilution for Easier Titration: It is easier to observe the endpoint of the titration, If the vinegar were too concentrated, the colour change might happen too quickly, making it harder to get an accurate measurement
- Does Not Affect Moles of Acetic Acid: does not change the number of moles of acetic acid present in the sample of vinegar, and the moles of titrant needed will still correspond to the moles of aceticacid in the original 5 mL of vinegar.
Common Errors During Titration
- Over titration
Addition of excess base/alkali, even after endpoint.
The colour should be light pink, not dark pink - Wrong reading from burette
When you write wrong reading from the buretteat the end point. (Always read bottom of meniscus).
Disposal
Chemicals Disposal (organic waste container).
Percent Difference
To achieve high accuracy, % difference should not exceed 1%. A higher percent difference may indicate inconsistencies between trials.
L - S / L × 100
