Analytical Chemistry II: Quantitative Analysis - SS3 Chemistry Past Questions and Answers - page 3
A mixture of iron filings and sulphur can be separated using a magnet. What property of iron allows it to be separated from sulphur using this method?
Iron is magnetic
Iron has a higher density than sulphur
Iron reacts with sulphur
Iron is soluble in water
Discuss the principles and applications of filtration as a separation technique. Provide examples of how filtration is used in various industries and research fields.
Filtration is a separation technique that relies on a porous barrier to separate solid particles from a liquid or gas based on particle size. The principle behind filtration is that smaller particles pass through the pores of the filter, while larger particles are retained, leading to the separation of the mixture. Filtration is widely used in industries and research fields for various purposes.
In the pharmaceutical industry, filtration is a crucial step in the production of drugs and medicines. It is used to remove impurities, separate crystals, and sterilise liquids. For example, during the manufacturing of antibiotics, filtration is employed to remove microbial contaminants, ensuring the final product is safe for consumption.
In environmental science and water treatment, filtration plays a vital role in purifying drinking water and wastewater. Large-scale filtration systems are used to remove suspended particles, sediments, and microorganisms, making water safe for human use and minimising environmental impacts.
Laboratories use filtration in research and analysis processes. For instance, in chemical analysis, filtration is utilised to separate a solid precipitate from a liquid solution after a chemical reaction. This enables researchers to isolate and study the solid compound further.
Describe the principles and applications of evaporation as a separation technique. Provide examples of how evaporation is used in different scientific and industrial settings.
Evaporation is a separation technique that involves the conversion of a liquid into its vapour phase, leaving behind solid solutes or concentrated solutions. The principle behind evaporation is the application of heat to increase the vapour pressure of the liquid, allowing molecules to escape from the liquid phase into the gas phase. The remaining substances become more concentrated as the liquid volume decreases.
Evaporation finds widespread applications in various scientific and industrial settings:
1. Salt Production: In the salt industry, seawater is collected in large shallow ponds. The sun's heat causes the water to evaporate, leaving behind crystallised salt, which is then harvested.
2. Food Processing: Evaporation is utilised in the food industry to concentrate liquid products like fruit juices and dairy. By evaporating water, the desired compounds become more concentrated, leading to higher quality and longer shelf life.
3. Separation of Solvents: In laboratories and chemical industries, evaporation is employed to separate solvents from dissolved substances. For instance, after a chemical reaction, a chemist may use rotary evaporators to remove the solvent and obtain the desired compound.
4. Desalination: In some regions, where freshwater is scarce, evaporation is part of the desalination process. Seawater is evaporated to leave the salts behind, and the condensed vapour is collected as freshwater.
5. Effluent Treatment: Evaporation is used in the treatment of industrial effluents to concentrate the pollutants for further processing or disposal.
6. Cooling Systems: Evaporative cooling systems use the principle of evaporation to cool down the air, commonly seen in air conditioners or cooling towers.
In conclusion, evaporation is a versatile separation technique widely used in industries ranging from food processing to environmental remediation. Its ability to concentrate solutions and separate solvents makes it an essential process in various scientific and industrial applications.
Which of the following statements about titration in volumetric analysis is correct?
Titration is used to determine the volume of a reactant in a solution.
Titration is a technique used to measure the mass of a solute in a solution.
Titration involves measuring the concentration of an unknown solution by reacting it with a known reagent of known concentration.
Titration is used to determine the colour of a solution.
During an acid-base titration, phenolphthalein is commonly used as an indicator. What colour change is observed when the endpoint is reached in an acid-base titration using phenolphthalein?
From pink to colourless
From colourless to pink
From yellow to orange
From colourless to yellow
In a redox titration, which species is used as the titrant?
Indicator
Analyte
Oxidising agent
Reducing agent
In a titration of potassium permanganate (KMnO₄) with sodium oxalate (Na₂C₂O₄), what is the balanced chemical equation?
2KMnO₄ + 5Na₂C₂O₄ → 2MnO₂ + 5Na₂CO₃ + 4CO₂
2KMnO₄ + 3Na₂C₂O₄ → 2MnO₂ + 3Na₂CO₃ + 2CO₂
KMnO₄ + Na₂C₂O₄ → MnO₂ + Na₂CO₃ + CO₂
2KMnO₄ + 5Na₂C₂O₄ → 2MnO₂ + 10Na₂CO₃ + 8CO₂
In an iodometric titration, which reagent is commonly used to release iodine for titration?
Sodium thiosulfate (Na₂S₂O₃)
Potassium iodide (KI)
Sodium hydroxide (NaOH)
Sodium carbonate (Na₂CO₃)
Which of the following is NOT a primary standard in titration analysis?
Sodium hydroxide (NaOH)
Potassium permanganate (KMnO₄)
Sulphuric acid (H₂SO₄)
Sodium chloride (NaCl)
In a back titration, why is an excess of reagent added initially to the analyte?
To speed up the reaction.
To ensure that all of the analyte reacts with the reagent.
To avoid the need for an indicator.
To increase the precision of the titration