Interview questions and their answers on titration

Introduction and outcome

The following are the most asked questions in pharma interviews:

What is the titration?

The process of determining of strength of a solution with the help of a standard solution (of known normality) is called titration.

What is the differance between Normality and molarity?

Normality describes the amount of gram equivalent of compound present in the solution whereas Molarity describes the number of moles present in the solution. For example: The molecular weight of sulfuric acid is 98.079. Hence, it 1M solution will be prepared by dissolving 98 grams of Sulfuric acid in 1000 ml of water whereas the 1N solution of Sulfuric acid will be prepared by dissolving 49 grams of Sulfuric acid) in 1000 ml of water.

What are the different types of volumetric titration?

Following are the different types of volumetric titration:

• Acid-base titration e.g. HCl titration with NaOH
• Oxidation-reduction titration e.g. Iodometric and Iodimetric titration
• Precipitation titration e.g. AgNO₃ titration
• Complexometric titration e.g. EDTA titration

Which indicator is used in EDTA titration?

Calmagite and Eriochrome Black

Which indicator is used in Iodometric titration?

Starch solution

Which indicator is used in Potassium permanganate (KMnO₄) titration?

Not any indicator. KMnO₄ acts as a self indicator.

Which indicator is used in non-aqueous titration?

crystal violet

Which indicators are used during acid-base titration?

Phenolphthalein and Methyl orange are used during acid base titration

Which indicator is used during precipitation(Silver nitrate) titration?

Potassium chromate solution

What is differance between Iodimetry and Iodometry titration?

In Iodometry titration, the standard solution of Iodine is used as a titrant whereas, in the Iodometry titration, the liberated Iodine (in the chemical reaction) is titrated with another titrant.

Why Potassium iodide (KI) is added during the preparation of 0.1N Iodine solution?

Iodine is slightly soluble in water. But in the presence of iodide ion of potassium iodide, it forms an {I₃}^–
unstable water-soluble Triiodide anion complex and dissolves quickly👇

Iodine + Iodide anion ⇌Triiodide anion  complex

That is why Potassium iodide is added during the preparation of 0.1N Iodine solution.

Why is starch added before the endpoint in iodometric titration?

Starch is made of Amylose and Amylopectin.

Amylose is a straight chain compound and it gives a blue colour with iodine and the chain assumes a spiral form. Amylopectin is the branched-chain form and it adsorbs to form a red-purple colour.

In water, starch gives a water-insoluble complex with iodine. This water-insoluble complex creates problems in detecting the actual endpoint. This means that the endpoint appears before the actual endpoint. That is why the starch indicator is added just before the end point when the colour is pale-straw yellow.

Abbreviations:

• N: Normality
• M: Molarity
• HCl: Hydrochloric acid
• NaOH: Sodium hydroxide
• AgNO₃: Silver nitrate