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.
- Gravimetric analysis is a quantitative method based on the measurement of:
- Volume
- Mass
- Potential
- Absorbance
- The substance that is separated and weighed in gravimetric analysis is called the:
- Titrant
- Analyte
- Precipitate
- Indicator
- The contamination of a precipitate by substances that are normally soluble in the mother liquor is known as:
- Post-precipitation
- Co-precipitation
- Digestion
- Ignition
- The process of allowing a precipitate to stand in the hot mother liquor to form larger, purer particles is called:
- Filtration
- Washing
- Ignition
- Digestion
- 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.
- The precipitation of an impurity on the surface of the primary precipitate after its formation is called:
- Co-precipitation
- Occlusion
- Post-precipitation
- Isomorphous replacement
- 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
- The process of strongly heating a precipitate to convert it into a stable weighing form is known as:
- Drying
- Digestion
- Ignition
- Peptization
- The entrapment of soluble impurities within a growing crystal during precipitation is termed:
- Surface adsorption
- Occlusion
- Post-precipitation
- Isomorphous replacement
- A good precipitating agent should ideally produce a precipitate that is:
- Crystalline and easily filterable
- Colloidal and gelatinous
- Highly soluble
- Very finely divided
- Washing the precipitate in gravimetric analysis is done to remove:
- The analyte itself
- Insoluble impurities
- The precipitating agent
- Adhering mother liquor and soluble impurities
- The “weighing form” of a precipitate should be:
- Hygroscopic
- Thermally stable and of a definite, known composition
- Volatile
- Highly reactive
- 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
- 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
- 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
- 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
- The process of converting a colloidal precipitate back into a dispersed state is known as:
- Coagulation
- Flocculation
- Peptization
- Digestion
- 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
- 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
- The estimation of barium as barium sulphate is an example of:
- Volatilization gravimetry
- Precipitation gravimetry
- Electrogravimetry
- Particulate gravimetry
- An ideal precipitate for gravimetric analysis should have a:
- High solubility product (Ksp)
- Low solubility product (Ksp)
- High hygroscopicity
- Small particle size
- 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.
- 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
- 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
- Which apparatus is commonly used for the ignition of a precipitate at high temperatures?
- Hot plate
- Water bath
- Drying oven
- Muffle furnace
- 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.
- A common example of post-precipitation is the precipitation of ______ on calcium oxalate.
- Magnesium oxalate
- Sodium chloride
- Barium sulphate
- Silver chloride
- Which of the following is NOT a step in gravimetric analysis?
- Precipitation
- Titration
- Filtration
- Weighing
- 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
- 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
- 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
- Digestion of a precipitate is also known as:
- Ostwald ripening
- Peptization
- Flocculation
- Ignition
- 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
- Which form of co-precipitation is the most difficult to minimize?
- Surface adsorption
- Occlusion
- Isomorphous replacement
- Post-precipitation
- 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
- 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.
- For a precipitate to be suitable for gravimetry, it should NOT be:
- Of known composition
- Easily filterable
- Pure
- Hygroscopic
- 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.
- 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
- The solubility of most precipitates, like BaSO₄, ______ with an increase in temperature.
- increases
- decreases
- remains unchanged
- becomes zero
- 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
- 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
- A disadvantage of gravimetric analysis is that it is often:
- Not very accurate
- Only applicable to colored compounds
- Time-consuming
- Not very precise
- Which is an example of an inorganic precipitating agent?
- Dimethylglyoxime
- 8-Hydroxyquinoline
- Ammonia
- Cupferron
- 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.
- What is the weighing form in the estimation of Barium?
- BaCl₂
- Ba(OH)₂
- BaSO₄
- BaCO₃
- The process of separating a precipitate from a liquid by passing it through a porous medium is:
- Digestion
- Ignition
- Filtration
- Precipitation
- Which of the following is NOT a type of co-precipitation?
- Peptization
- Surface adsorption
- Occlusion
- Isomorphous replacement
- 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
- 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
