Lab 6 - Titration

Question 1

Titration

Answer 1

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.

Question 2

Types of titration

Answer 2

1. Redox titration
2. Precipitation Titration
3. Complexometry titration
4. Non- aqueous titration
5. Acid-base titration

Question 3

Why is titration used in pharmacy?

Answer 3

Determining the Concentration of Active Ingredients Quality Control and Purity Testing
Drug Stability Testing
Determining Solubility and Dissolution
Assaying Complexes and Chelates

Question 4

Redox reaction

Answer 4

reduction-oxidation reaction occurs between the titrant and the analyte. The titrant donates or accepts electrons, changing the oxidation state of the analyte

Question 5

Indicator reaction

Answer 5

Redox indicators or changes in colour due to oxidation state shifts

Question 6

Example of redox titrations

Answer 6

Titration of iron (II) ions (Fe²⁺) with potassium permanganate (KMnO₄) (strong oxidizing agent)

Question 7

Precipitation reaction

Answer 7

reaction between the titrant and analyte forms an insoluble precipitate

Question 8

Precipitation indicator

Answer 8

the appearance or disappearance of a precipitate

Question 9

Precipitation example

Answer 9

Titration of chloride ions (Cl⁻) with silver nitrate (AgNO₃) forming AgCl (s)

Question 10

Complexometry reaction

Answer 10

involves the formation of a complex ion between the analyte (often a metal ion) and the titrant(typically a chelating agent like EDTA)

Question 11

Complexometry indicator

Answer 11

Metal ion indicators, which change colour when metal ions are free or bound to the complexing agent

Question 12

Complexometry example

Answer 12

Titration of calcium ions (Ca²⁺) with EDTA (Ethylenediaminetetraacetic acid)

Question 13

Non aqueous reaction

Answer 13

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)

Question 14

Non aqueous indicators

Answer 14

Acid-base indicators

Question 15

Non aqueous example

Answer 15

Titration of a weak acid like benzoic acid (C₆H₅COOH) in glacial acetic acid using a non-aqueous base like sodium methoxide (NaOCH₃) (strong base)

Question 16

Acid - base reaction

Answer 16

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.

Question 17

Acid-base indicator

Answer 17

Acid-base indicators

Question 18

Acid-base example

Answer 18

Titration of acetic acid (CH₃COOH) with sodium hydroxide (NaOH)
Strong base, weak acid

Question 19

What are the indicators?

Answer 19

An indicator is an organic compound that changes the colour of the solution at the endpoint/ equivalence point.

Question 20

Acid-base indicators are composed of

Answer 20

These indicators are either weak acid or weak base.

Question 21

Equivalence point

Answer 21

No. of moles of H+ = No.of moles of OH-

Question 22

True or false
The equivalence point can be determined 100%

Answer 22

False

Question 23

Phenolphthalein

Answer 23

pH range 8-10
Colourless in acidic
Basic in medium

Question 24

Phenolpthalein

Answer 24

• 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

Question 25

Calculations at the equivalent point

Answer 25

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.

Question 26

Stoichiometric factor, fa

Answer 26

It represents the number of protons (H⁺ ions) that can be donated

1. 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+
2. 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⁻
3. 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⁻

Question 27

Stoichiometric Factor, fb

Answer 27

It represents the number of protons (H⁺ ions) that are accepted or hydroxide ions (OH⁻) that can be donated

1. Monobasic Bases
   A base that can accept only one proton (or donate one hydroxide ion, OH⁻).
   Sodium hydroxide (NaOH): NaOH → Na⁺ + OH⁻
2. 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⁻

Question 28

Molarity

Answer 28

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.

Question 29

Normality

Answer 29

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

Question 30

Why do we dilute?

Answer 30

it doesn’t affect the outcome of the titration in terms of the concentration of acetic acid being analyzed.

1. 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
2. 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.

Question 31

Common Errors During Titration

Answer 31

1. Over titration
   Addition of excess base/alkali, even after endpoint.
   The colour should be light pink, not dark pink
2. Wrong reading from burette
   When you write wrong reading from the buretteat the end point. (Always read bottom of meniscus).

Question 32

Disposal

Answer 32

Chemicals Disposal (organic waste container).

Question 33

Percent Difference

Answer 33

To achieve high accuracy, % difference should not exceed 1%. A higher percent difference may indicate inconsistencies between trials.
L - S / L × 100