Primary and secondary standards MCQs With Answer

Primary and secondary standards MCQs With Answer is a focused practice set for B. Pharm students to master standardization concepts in pharmaceutics and analytical chemistry. This collection covers definitions, criteria for primary standards (purity, stability, non-hygroscopic nature, known stoichiometry), common primary examples (KHP, potassium dichromate), why reagents like NaOH are secondary, and methods of preparing and standardizing titrants. Questions emphasize assay accuracy, titrimetric calculations, equivalence factors, endpoint detection, storage, traceability and pharmacopoeial compliance. Each MCQ reinforces understanding of volumetric analysis, calibration, and good laboratory practice essential for pharmaceutical analysis. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What is a primary standard in analytical chemistry?

• A reagent of very high purity used to prepare a solution of known concentration
• A colored indicator used to detect end point
• A volumetric flask used for dilutions
• A buffer solution for pH calibration

Correct Answer: A reagent of very high purity used to prepare a solution of known concentration

Q2. Which of the following is NOT a desirable criterion for a primary standard?

• High purity and stable composition
• Non-hygroscopic and does not absorb CO2 from air
• Low molar mass to minimize weighing error
• Known and unambiguous stoichiometry

Correct Answer: Low molar mass to minimize weighing error

Q3. Which compound is commonly used as a primary standard for acid-base titrations?

• Potassium hydrogen phthalate (KHP)
• Sodium hydroxide solution
• Hydrochloric acid solution
• Phenolphthalein indicator

Correct Answer: Potassium hydrogen phthalate (KHP)

Q4. Why is commercial sodium hydroxide typically treated as a secondary standard?

• It absorbs carbon dioxide and moisture from air, altering concentration
• It has an extremely high molar mass
• It is insoluble in water
• It is always available as a primary standard

Correct Answer: It absorbs carbon dioxide and moisture from air, altering concentration

Q5. Which reagent is a common primary standard for redox titrations?

• Potassium dichromate (K2Cr2O7)
• Potassium permanganate (KMnO4) unstandardized
• Sodium thiosulfate directly without standardization
• Phenolphthalein

Correct Answer: Potassium dichromate (K2Cr2O7)

Q6. How is a secondary standard defined in volumetric analysis?

• A solution whose exact concentration is determined by titration against a primary standard
• A chemical of absolute purity used without standardization
• An indicator solution used to detect end point
• A solid reagent used directly as a titrant

Correct Answer: A solution whose exact concentration is determined by titration against a primary standard

Q7. What is meant by ‘standardization’ of a volumetric solution?

• Determination of the exact concentration of the solution by titration with a primary standard
• Preparing a solution by diluting distilled water only
• Heating the solution to constant volume
• Adding indicator to a solution without titration

Correct Answer: Determination of the exact concentration of the solution by titration with a primary standard

Q8. The equivalence factor used to convert between molarity and normality is BEST described as:

• The number of equivalents per mole of a substance (valence factor)
• The pH at equivalence point
• The molar mass divided by Avogadro’s number
• The volume of titrant required to reach end point

Correct Answer: The number of equivalents per mole of a substance (valence factor)

Q9. Which primary standard is commonly used to standardize sodium hydroxide solutions?

• Potassium hydrogen phthalate (KHP)
• Hydrochloric acid
• Sodium chloride
• Phenolphthalein

Correct Answer: Potassium hydrogen phthalate (KHP)

Q10. Why is a high molar mass advantageous for a primary standard?

• It reduces relative weighing errors and improves accuracy of prepared solution
• It increases volatility for easy handling
• It makes the compound more hygroscopic
• It always makes the compound colored for visual checks

Correct Answer: It reduces relative weighing errors and improves accuracy of prepared solution

Q11. What is the chemical name of KHP used as a primary standard?

• Potassium hydrogen phthalate
• Potassium hydroxide phthalate
• Potassium phthalate dibasic
• Potassium hydrogen phosphate

Correct Answer: Potassium hydrogen phthalate

Q12. Which end-point detection method is generally more precise than visual indicators?

• Potentiometric titration using an electrode
• Using a colored paper strip
• Estimating by smell
• Weighing the titrant directly during titration

Correct Answer: Potentiometric titration using an electrode

Q13. Which property makes potassium dichromate a suitable primary standard for certain redox titrations?

• High purity, stability and well-defined stoichiometry
• Strong hygroscopic nature
• Rapid decomposition in air
• Low molar mass

Correct Answer: High purity, stability and well-defined stoichiometry

Q14. Which of the following is hygroscopic and therefore unsuitable as a primary standard solid?

• Sodium hydroxide (NaOH)
• Potassium hydrogen phthalate (KHP)
• Potassium dichromate (K2Cr2O7)
• Potassium chloride (KCl)

Correct Answer: Sodium hydroxide (NaOH)

Q15. The main purpose of preparing a secondary standard is to:

• Obtain a working solution of known concentration through standardization
• Have a reagent that never requires calibration
• Create an indicator solution for titration
• Produce a solid primary standard

Correct Answer: Obtain a working solution of known concentration through standardization

Q16. Potassium permanganate (KMnO4) is often standardized before use because:

• Its exact concentration varies and it undergoes side reactions and decomposition
• It is always a primary standard and requires no standardization
• It is colorless by nature
• It has no redox activity

Correct Answer: Its exact concentration varies and it undergoes side reactions and decomposition

Q17. Best storage conditions for a primary standard solid are:

• Tightly closed container, dry place or desiccator, away from CO2
• Open container on the bench exposed to air
• Stored in dilute aqueous solution
• Kept in direct sunlight

Correct Answer: Tightly closed container, dry place or desiccator, away from CO2

Q18. One advantage of using a primary standard is:

• Traceability to mass measurement and high accuracy in concentration
• It eliminates need for any titration
• It always has a colored endpoint
• It allows indefinite storage as aqueous solution without change

Correct Answer: Traceability to mass measurement and high accuracy in concentration

Q19. How many grams of KHP (molar mass 204.22 g·mol−1) are required to prepare 250 mL of 0.1 N solution? (KHP is monoprotic)

• 5.105 g of KHP
• 0.5105 g of KHP
• 51.05 g of KHP
• 2.042 g of KHP

Correct Answer: 5.105 g of KHP

Q20. Which indicator is commonly used for titration of a weak acid with a strong base when the end point is above pH 8?

• Phenolphthalein
• Methyl orange
• Bromothymol blue for pH below 4
• Starch for non-redox acid-base titrations

Correct Answer: Phenolphthalein

Q21. Which statement about potassium hydrogen phthalate (KHP) is TRUE?

• It is stable, non-hygroscopic, and has a known molecular weight suitable for primary standard use
• It readily absorbs CO2 and is unsuitable as a standard
• It decomposes at room temperature and cannot be weighed accurately
• It is only used as an indicator

Correct Answer: It is stable, non-hygroscopic, and has a known molecular weight suitable for primary standard use

Q22. A secondary standard solution is usually prepared by:

• Standardizing a convenient titrant (e.g., NaOH) against a primary standard
• Directly using commercial reagents without checking concentration
• Mixing two colored indicators
• Heating a primary standard to evaporate impurities

Correct Answer: Standardizing a convenient titrant (e.g., NaOH) against a primary standard

Q23. Using an impure substance incorrectly labeled as a primary standard will mainly introduce what type of error?

• Systematic error in the concentration of prepared solutions
• Random error that cancels out over repeated trials
• Improved precision but reduced accuracy
• No error if indicator color change is observed

Correct Answer: Systematic error in the concentration of prepared solutions

Q24. The equivalence point in a titration is defined as the point at which:

• The stoichiometric amounts of titrant and analyte have reacted
• The first drop of titrant is added
• The indicator color starts to fade slightly
• The solution reaches boiling point

Correct Answer: The stoichiometric amounts of titrant and analyte have reacted

Q25. For a primary standard solid, why is low hygroscopicity important?

• It prevents mass change due to moisture uptake, ensuring accurate weighing
• It increases the reaction rate in titration
• It guarantees the solid is colored for easy handling
• It makes the substance volatile

Correct Answer: It prevents mass change due to moisture uptake, ensuring accurate weighing

Q26. Which of the following solids can typically be used as a primary standard by direct weighing?

• Potassium dichromate (K2Cr2O7)
• Commercial sodium hydroxide pellets without drying
• Potassium permanganate directly without standardization
• Liquid hydrochloric acid

Correct Answer: Potassium dichromate (K2Cr2O7)

Q27. In alkalimetry, which titrant must always be standardized before use as a titrant?

• Sodium hydroxide (NaOH)
• Potassium hydrogen phthalate (KHP) as reagent
• Phenolphthalein indicator
• Distilled water

Correct Answer: Sodium hydroxide (NaOH)

Q28. Back titration is preferred when:

• The analyte reacts slowly with the titrant or direct titration is impractical
• The titration is extremely fast and visual end point is sharp
• No primary standard is available and none is needed
• The analyte is volatile and cannot be contained

Correct Answer: The analyte reacts slowly with the titrant or direct titration is impractical

Q29. The titrimetric term ‘titer’ most nearly means:

• The mass of analyte that reacts with 1 mL of a titrant solution
• The pH at which the indicator changes color
• The molar mass divided by the volume of titrant used
• The number of drops of indicator added

Correct Answer: The mass of analyte that reacts with 1 mL of a titrant solution

Q30. Which practice helps maintain accuracy of a secondary standard over time?

• Periodic re-standardization against a fresh primary standard
• Leaving the solution open to air for equilibration
• Heating the solution frequently to refresh concentration
• Adding excess indicator at storage

Correct Answer: Periodic re-standardization against a fresh primary standard

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