MCQ Quiz- Gravimetry

MCQ Quiz: Gravimetry

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Gravimetric analysis represents a cornerstone of quantitative chemical analysis, valued for its high accuracy and precision. For B.Pharm students, understanding the principles of gravimetry is essential for the absolute measurement of an analyte’s mass, a critical skill in the quality control and standardization of raw materials and finished pharmaceutical products. This quiz covers the fundamental steps, principles, and potential sources of error, such as co-precipitation and post-precipitation.

  1. Gravimetric analysis is a quantitative method based on the measurement of:
    • Volume
    • Mass
    • Potential
    • Absorbance
    Answer: Mass
  2. The substance that is separated and weighed in gravimetric analysis is called the:
    • Titrant
    • Analyte
    • Precipitate
    • Indicator
    Answer: Precipitate
  3. The contamination of a precipitate by substances that are normally soluble in the mother liquor is known as:
    • Post-precipitation
    • Co-precipitation
    • Digestion
    • Ignition
    Answer: Co-precipitation
  4. The process of allowing a precipitate to stand in the hot mother liquor to form larger, purer particles is called:
    • Filtration
    • Washing
    • Ignition
    • Digestion
    Answer: Digestion
  5. Which of the following is a crucial step in gravimetric analysis?
    • Ensuring the precipitate is completely insoluble.
    • Converting the precipitate to a pure substance of known composition.
    • Washing the precipitate to remove soluble impurities.
    • All of the above.
    Answer: All of the above.
  6. The precipitation of an impurity on the surface of the primary precipitate after its formation is called:
    • Co-precipitation
    • Occlusion
    • Post-precipitation
    • Isomorphous replacement
    Answer: Post-precipitation
  7. In the estimation of sulphate ions as barium sulphate, which reagent is used as the precipitating agent?
    • Silver nitrate
    • Barium chloride
    • Lead acetate
    • Hydrochloric acid
    Answer: Barium chloride
  8. The process of strongly heating a precipitate to convert it into a stable weighing form is known as:
    • Drying
    • Digestion
    • Ignition
    • Peptization
    Answer: Ignition
  9. The entrapment of soluble impurities within a growing crystal during precipitation is termed:
    • Surface adsorption
    • Occlusion
    • Post-precipitation
    • Isomorphous replacement
    Answer: Occlusion
  10. A good precipitating agent should ideally produce a precipitate that is:
    • Crystalline and easily filterable
    • Colloidal and gelatinous
    • Highly soluble
    • Very finely divided
    Answer: Crystalline and easily filterable
  11. Washing the precipitate in gravimetric analysis is done to remove:
    • The analyte itself
    • Insoluble impurities
    • The precipitating agent
    • Adhering mother liquor and soluble impurities
    Answer: Adhering mother liquor and soluble impurities
  12. The “weighing form” of a precipitate should be:
    • Hygroscopic
    • Thermally stable and of a definite, known composition
    • Volatile
    • Highly reactive
    Answer: Thermally stable and of a definite, known composition
  13. When two compounds have the same crystal structure and can form mixed crystals, the resulting co-precipitation is called:
    • Occlusion
    • Surface adsorption
    • Isomorphous replacement
    • Post-precipitation
    Answer: Isomorphous replacement
  14. The gravimetric factor is a conversion factor that relates:
    • The mass of the precipitate to the mass of the analyte
    • The volume of the titrant to the mass of the analyte
    • The mass of the precipitate to its molar mass
    • The mass of the analyte to its molar mass
    Answer: The mass of the precipitate to the mass of the analyte
  15. What is the first step in a typical gravimetric analysis by precipitation?
    • Filtering the precipitate
    • Adding the precipitating agent to the sample solution
    • Weighing the final precipitate
    • Drying the precipitate
    Answer: Adding the precipitating agent to the sample solution
  16. Which of the following helps in reducing co-precipitation?
    • Rapid precipitation from a concentrated solution
    • Slow precipitation from a dilute, hot solution
    • Using a large excess of the precipitating agent
    • Avoiding the washing step
    Answer: Slow precipitation from a dilute, hot solution
  17. The process of converting a colloidal precipitate back into a dispersed state is known as:
    • Coagulation
    • Flocculation
    • Peptization
    • Digestion
    Answer: Peptization
  18. The primary contaminant in co-precipitation by surface adsorption is an impurity that is:
    • Trapped inside the crystal
    • Bound to the surface of the precipitate
    • Chemically similar to the analyte
    • Precipitated after the main precipitate
    Answer: Bound to the surface of the precipitate
  19. To prevent peptization during the washing step, one should use a wash liquid containing:
    • A volatile electrolyte
    • A non-polar solvent
    • A strong acid
    • Pure distilled water only
    Answer: A volatile electrolyte
  20. The estimation of barium as barium sulphate is an example of:
    • Volatilization gravimetry
    • Precipitation gravimetry
    • Electrogravimetry
    • Particulate gravimetry
    Answer: Precipitation gravimetry
  21. An ideal precipitate for gravimetric analysis should have a:
    • High solubility product (Ksp)
    • Low solubility product (Ksp)
    • High hygroscopicity
    • Small particle size
    Answer: Low solubility product (Ksp)
  22. The main difference between co-precipitation and post-precipitation is that:
    • Co-precipitation involves soluble impurities, while post-precipitation involves insoluble ones.
    • Co-precipitation occurs during the formation of the precipitate, while post-precipitation occurs after.
    • Co-precipitation can be minimized, while post-precipitation cannot.
    • Co-precipitation is desirable, while post-precipitation is not.
    Answer: Co-precipitation occurs during the formation of the precipitate, while post-precipitation occurs after.
  23. The main purpose of the digestion of a precipitate is to:
    • Increase the surface area
    • Increase the particle size and purity
    • Decrease the solubility
    • Remove water of hydration
    Answer: Increase the particle size and purity
  24. In the gravimetric analysis of barium sulphate, why is the solution acidified?
    • To increase the solubility of BaSO₄
    • To prevent the co-precipitation of other barium salts like barium carbonate
    • To speed up the reaction
    • To dissolve the precipitate
    Answer: To prevent the co-precipitation of other barium salts like barium carbonate
  25. Which apparatus is commonly used for the ignition of a precipitate at high temperatures?
    • Hot plate
    • Water bath
    • Drying oven
    • Muffle furnace
    Answer: Muffle furnace
  26. Post-precipitation is a significant problem when:
    • The primary precipitate has a high surface area.
    • The solution contains an impurity that forms a sparingly soluble substance with the precipitating agent.
    • The digestion process is too long.
    • The solution is too dilute.
    Answer: The solution contains an impurity that forms a sparingly soluble substance with the precipitating agent.
  27. A common example of post-precipitation is the precipitation of ______ on calcium oxalate.
    • Magnesium oxalate
    • Sodium chloride
    • Barium sulphate
    • Silver chloride
    Answer: Magnesium oxalate
  28. Which of the following is NOT a step in gravimetric analysis?
    • Precipitation
    • Titration
    • Filtration
    • Weighing
    Answer: Titration
  29. The gravimetric factor for converting BaSO₄ to SO₄²⁻ is calculated as:
    • Molar mass of SO₄²⁻ / Molar mass of BaSO₄
    • Molar mass of BaSO₄ / Molar mass of SO₄²⁻
    • Molar mass of Ba / Molar mass of BaSO₄
    • Molar mass of S / Molar mass of BaSO₄
    Answer: Molar mass of SO₄²⁻ / Molar mass of BaSO₄
  30. Which type of filter paper is used for filtering fine crystalline precipitates in gravimetry?
    • Coarse filter paper
    • Ashless filter paper
    • Hardened filter paper
    • Qualitative filter paper
    Answer: Ashless filter paper
  31. The final constant weight is obtained in gravimetry by:
    • Repeated cycles of heating, cooling, and weighing
    • A single heating step
    • Measuring the volume accurately
    • Using a catalyst
    Answer: Repeated cycles of heating, cooling, and weighing
  32. Digestion of a precipitate is also known as:
    • Ostwald ripening
    • Peptization
    • Flocculation
    • Ignition
    Answer: Ostwald ripening
  33. The key to a successful gravimetric analysis is the:
    • Choice of indicator
    • Speed of the reaction
    • Purity and known stoichiometry of the final precipitate
    • Use of a non-aqueous solvent
    Answer: Purity and known stoichiometry of the final precipitate
  34. Which form of co-precipitation is the most difficult to minimize?
    • Surface adsorption
    • Occlusion
    • Isomorphous replacement
    • Post-precipitation
    Answer: Isomorphous replacement
  35. The mother liquor is the:
    • Wash solution used to clean the precipitate
    • Pure solvent used to dissolve the sample
    • Solution from which the precipitate was formed
    • Standard solution used for titration
    Answer: Solution from which the precipitate was formed
  36. Gravimetry is considered an “absolute method” because:
    • It is always 100% accurate.
    • It relies on the absolute measurement of mass and known stoichiometric relationships.
    • It requires an absolute zero temperature.
    • It does not require calibration.
    Answer: It relies on the absolute measurement of mass and known stoichiometric relationships.
  37. For a precipitate to be suitable for gravimetry, it should NOT be:
    • Of known composition
    • Easily filterable
    • Pure
    • Hygroscopic
    Answer: Hygroscopic
  38. The term ‘supersaturation’ in precipitation refers to a solution state where:
    • The solvent is completely saturated.
    • The concentration of solute is greater than its equilibrium solubility.
    • The precipitate is forming rapidly.
    • The solution is heated.
    Answer: The concentration of solute is greater than its equilibrium solubility.
  39. Which of these errors leads to a lower result in gravimetric analysis?
    • Incomplete precipitation of the analyte
    • Co-precipitation of a more massive impurity
    • Incomplete drying of the precipitate
    • Insufficient washing
    Answer: Incomplete precipitation of the analyte
  40. The solubility of most precipitates, like BaSO₄, ______ with an increase in temperature.
    • increases
    • decreases
    • remains unchanged
    • becomes zero
    Answer: increases
  41. What is the purpose of a desiccator in gravimetric analysis?
    • To heat the precipitate to a high temperature
    • To allow the hot crucible and precipitate to cool in a dry atmosphere without absorbing moisture
    • To filter the precipitate under vacuum
    • To wash the precipitate with an electrolyte
    Answer: To allow the hot crucible and precipitate to cool in a dry atmosphere without absorbing moisture
  42. A precipitating agent added as a dilute solution promotes the formation of:
    • A colloidal precipitate
    • Larger, more perfect crystals
    • A supersaturated solution
    • A gelatinous precipitate
    Answer: Larger, more perfect crystals
  43. A disadvantage of gravimetric analysis is that it is often:
    • Not very accurate
    • Only applicable to colored compounds
    • Time-consuming
    • Not very precise
    Answer: Time-consuming
  44. Which is an example of an inorganic precipitating agent?
    • Dimethylglyoxime
    • 8-Hydroxyquinoline
    • Ammonia
    • Cupferron
    Answer: Ammonia
  45. The purity of the precipitate is a critical factor because:
    • Impurities can add to the weight of the precipitate, causing a positive error.
    • Impurities can react with the precipitate.
    • Impurities change the color of the precipitate.
    • Impurities make the precipitate more soluble.
    Answer: Impurities can add to the weight of the precipitate, causing a positive error.
  46. What is the weighing form in the estimation of Barium?
    • BaCl₂
    • Ba(OH)₂
    • BaSO₄
    • BaCO₃
    Answer: BaSO₄
  47. The process of separating a precipitate from a liquid by passing it through a porous medium is:
    • Digestion
    • Ignition
    • Filtration
    • Precipitation
    Answer: Filtration
  48. Which of the following is NOT a type of co-precipitation?
    • Peptization
    • Surface adsorption
    • Occlusion
    • Isomorphous replacement
    Answer: Peptization
  49. Checking for the completeness of precipitation is done by:
    • Adding more sample solution
    • Adding a few more drops of the precipitating agent to the clear supernatant
    • Heating the solution
    • Weighing the precipitate
    Answer: Adding a few more drops of the precipitating agent to the clear supernatant
  50. The main objective of all the steps in gravimetric analysis is to:
    • Get the largest possible amount of precipitate
    • Isolate the analyte in the form of a pure, stable compound of known composition
    • Complete the analysis as quickly as possible
    • Use the least amount of precipitating agent
    Answer: Isolate the analyte in the form of a pure, stable compound of known composition

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