Redox titrations are a versatile and essential class of analytical methods in pharmaceutical chemistry. For B.Pharm students, understanding these titrations—which are based on oxidation-reduction reactions—is crucial for the assay of a wide range of drug substances. This quiz covers the fundamental concepts of oxidation and reduction, as well as the principles and applications of specific methods like iodometry, cerimetry, and bromatometry.
- Redox titrations are based on reactions that involve the transfer of:
- Protons
- Electrons
- Neutrons
- Hydride ions
- The process of losing one or more electrons is known as:
- Reduction
- Oxidation
- Hydrolysis
- Neutralization
- A substance that gains electrons in a redox reaction is called a(n):
- Reducing agent
- Oxidizing agent
- Catalyst
- Indicator
- In iodimetry, the substance being analyzed is directly titrated with a standard solution of:
- Iodine
- Sodium thiosulphate
- Potassium permanganate
- Ceric sulphate
- Iodometry is an indirect method where an oxidizing agent liberates iodine, which is then titrated with:
- Potassium dichromate
- Ceric ammonium sulphate
- Sodium thiosulphate
- Iodine
- Which of the following acts as a self-indicator in redox titrations?
- Starch
- Potassium permanganate
- Diphenylamine
- Eosin
- Cerimetry is a type of redox titration that uses which substance as the standard titrant?
- Ceric (Ce⁴⁺) salts
- Ferrous (Fe²⁺) salts
- Iodine
- Potassium dichromate
- The indicator most commonly used in titrations involving iodine is:
- Methyl orange
- Phenolphthalein
- Starch
- Eriochrome Black T
- The gain of one or more electrons is defined as:
- Oxidation
- Reduction
- Sublimation
- Precipitation
- A substance that causes another substance to be reduced is a(n):
- Oxidizing agent
- Reducing agent
- Acid
- Base
- Dichrometry uses which of the following as the primary standard oxidizing agent?
- Potassium permanganate
- Potassium dichromate
- Ceric sulphate
- Iodine
- What color does the starch indicator give in the presence of free iodine?
- Red
- Colorless
- Pink
- Intense blue
- Iodimetry is used for the quantitative estimation of:
- Oxidizing agents
- Reducing agents
- Acids
- Bases
- In the reaction Zn → Zn²⁺ + 2e⁻, the zinc atom is:
- Reduced
- Oxidized
- Neutralized
- Precipitated
- Which of the following is an example of an internal redox indicator?
- Starch
- Diphenylamine
- Potassium ferricyanide
- Potassium permanganate
- Bromatometry involves the use of a standard solution of:
- Potassium bromide
- Potassium bromate
- Bromine water
- Hydrobromic acid
- Titrations with potassium iodate are often carried out in a strong:
- Basic medium
- Acidic medium
- Neutral medium
- Non-aqueous medium
- The main advantage of using potassium dichromate as a titrant is that it:
- Is a strong oxidizing agent.
- Acts as its own indicator.
- Is available in high purity and is stable.
- Is inexpensive.
- An oxidizing agent is a substance that:
- Donates electrons
- Accepts electrons
- Donates protons
- Accepts protons
- Cerimetry is often preferred over permanganometry because:
- Ceric solutions are more stable than permanganate solutions.
- It does not require an indicator.
- It is a much stronger oxidizing agent.
- It can only be used in basic solutions.
- The oxidation state of manganese in KMnO₄ is:
- +2
- +4
- +5
- +7
- In iodometry, the analyte is typically a(n):
- Reducing agent
- Oxidizing agent
- Weak acid
- Weak base
- Why is the starch indicator added only near the end point in an iodometric titration?
- To prevent the formation of an irreversible starch-iodine complex at high iodine concentrations.
- The indicator is unstable in acidic solution.
- The indicator only works in a narrow pH range.
- To prevent the indicator from reacting with the thiosulphate.
- A reducing agent is a substance that:
- Is oxidized in a redox reaction.
- Is reduced in a redox reaction.
- Increases in oxidation number.
- Gains electrons.
- The reaction 2S₂O₃²⁻ → S₄O₆²⁻ + 2e⁻ occurs during the titration of iodine with:
- Ceric sulphate
- Sodium thiosulphate
- Potassium permanganate
- Ferrous sulphate
- Ferroin is a common indicator used in:
- Iodometry
- Permanganometry
- Cerimetry
- Bromatometry
- What happens to the oxidation number of a substance when it is oxidized?
- It decreases.
- It increases.
- It remains the same.
- It becomes zero.
- Titrations involving potassium permanganate are usually carried out in a strongly ______ solution.
- acidic
- basic
- neutral
- alcoholic
- Which of the following represents a reduction?
- Fe²⁺ → Fe³⁺
- Cr₂O₇²⁻ → 2Cr³⁺
- 2Cl⁻ → Cl₂
- H₂S → S
- What is the purpose of adding excess potassium iodide in an iodometric titration?
- To act as an indicator.
- To react with the oxidizing analyte to liberate a stoichiometric amount of iodine.
- To buffer the solution.
- To precipitate the analyte.
- The concept of oxidation can be defined as:
- A gain of hydrogen
- A loss of oxygen
- A loss of electrons
- A decrease in oxidation number
- In dichrometry, the change in oxidation state for chromium is from:
- +3 to +6
- +6 to +3
- +2 to +3
- +7 to +2
- Which titration involves the use of a standard solution of a reducing agent?
- Cerimetry
- Permanganometry
- Iodimetry
- Dichrometry
- The disappearance of the blue color at the end point of an iodometric titration signifies that:
- All the liberated iodine has reacted with the thiosulphate.
- The reaction has reached equilibrium.
- All the thiosulphate has been consumed.
- The pH has become neutral.
- The primary standard used to standardize KMnO₄ solutions is often:
- Sodium hydroxide
- Sodium oxalate
- Sodium chloride
- Sodium carbonate
- The concept of reduction can be defined as:
- A loss of hydrogen
- A gain of oxygen
- A gain of electrons
- An increase in oxidation number
- A redox indicator must have:
- A different color in its oxidized and reduced forms.
- A high molecular weight.
- The ability to act as a primary standard.
- The ability to fluoresce.
- Which of these titrations is typically used to determine the concentration of copper sulphate?
- Cerimetry
- Iodometry
- Acid-base titration
- Complexometric titration
- What happens to the oxidation number of a substance when it is reduced?
- It decreases.
- It increases.
- It stays the same.
- It doubles.
- Which substance is both an oxidizing agent and a primary standard?
- Potassium permanganate
- Sodium thiosulphate
- Potassium dichromate
- Iodine
- The solution of sodium thiosulphate is standardized by titrating it against:
- An acid
- A base
- A standard solution of iodine (liberated from KIO₃ or K₂Cr₂O₇)
- A standard solution of silver nitrate
- The end point of a permanganate titration is a persistent:
- Blue color
- Pink color
- Yellow color
- Colorless solution
- A key feature of redox reactions is that oxidation and reduction must:
- Occur in separate steps
- Occur simultaneously
- Be catalyzed
- Be reversible
- What is the function of Zimmermann-Reinhardt reagent in permanganate titrations?
- To act as an indicator
- To prevent the oxidation of chloride ions by permanganate
- To buffer the solution
- To act as a catalyst
- Which method would be suitable for the assay of hydrogen peroxide (a reducing agent)?
- Iodometry
- Permanganometry
- Complexometric titration
- Non-aqueous titration
- The reaction I₂ + 2e⁻ → 2I⁻ is a(n):
- Oxidation half-reaction
- Reduction half-reaction
- Acid-base reaction
- Precipitation reaction
- Titrations involving iodine are sensitive to:
- pH changes
- Temperature
- The presence of light
- All of the above
- In cerimetry, the reaction involves the conversion of:
- Ce⁴⁺ to Ce³⁺
- Ce³⁺ to Ce⁴⁺
- Fe²⁺ to Fe³⁺
- MnO₄⁻ to Mn²⁺
- In which titration is the titrant itself the reducing agent?
- Dichrometry
- Permanganometry
- Cerimetry
- Iodimetry (using a substance like arsenite titrated with iodine)
- The main advantage of using potassium iodate as a titrant is its:
- Intense color
- High stability as a primary standard
- Strong reducing power
- Low molecular weight
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