IGCSE Chemistry Alternative to Practical

Explain how you would test for the presence of carbon dioxide gas in a given sample using limewater.

• Pass the gas through limewater and observe the formation of a white precipitate.

• Shake the limewater vigorously and observe any changes

• Heat the limewater and observe the color change

• Mix the limewater with vinegar and observe the reaction

Describe a method to determine the melting point of a solid substance.

• Observing the substance under a microscope

• Using a melting point apparatus and recording the temperature at which the solid substance begins to melt.

• Using a thermometer to measure the color change of the substance

• Heating the substance until it turns black

Outline the steps involved in preparing a standard solution of sodium carbonate.

• Prepare a standard solution of sodium carbonate by weighing the compound, dissolving it in water in a volumetric flask, filling up to the mark, mixing thoroughly, and labeling appropriately.

• Skip the labeling step

• Heat the compound in an open flame

• Use a dirty volumetric flask for dissolving

Discuss the procedure for testing the presence of chloride ions in a solution.

• Heat the solution and check for the release of a pungent odor to detect chloride ions.

• Add sodium chloride (NaCl) to the solution and observe the color change to confirm the presence of chloride ions.

• Add silver nitrate (AgNO3) to the solution and observe the formation of a white precipitate of silver chloride (AgCl) to confirm the presence of chloride ions.

• Mix the solution with potassium iodide (KI) and look for the formation of a yellow precipitate to identify chloride ions.

Explain how you would investigate the rate of reaction between hydrochloric acid and magnesium ribbon.

• Use a ruler to measure the color change of the reaction mixture

• Heat the reaction mixture to speed up the reaction

• Mix the hydrochloric acid and magnesium ribbon in a closed container to prevent gas escape

• Measure the initial mass of magnesium ribbon, add hydrochloric acid, monitor hydrogen gas volume produced over time.

Describe a method to separate a mixture of sand and salt.

• Add oil, heat, evaporate

• Add water, filter, evaporate

• Add sugar, dissolve, evaporate

• Add vinegar, filter, evaporate

Outline the steps to determine the concentration of a hydrochloric acid solution using a standard solution of sodium hydroxide.

• The concentration of the hydrochloric acid solution can be determined by titrating it with a standard solution of potassium hydroxide.

• The concentration of the hydrochloric acid solution can be determined by titrating it with a standard solution of sodium hydroxide and using the volume and concentration of the sodium hydroxide solution.

• The concentration of the hydrochloric acid solution can be determined by heating the solution to evaporate the water content.

• The concentration of the hydrochloric acid solution can be determined by using a pH meter to measure the acidity.

Discuss the procedure for testing the presence of starch in a food sample.

• Heat the food sample, if it turns green, starch is present

• Perform the iodine test by applying iodine solution to the food sample. A blue-black color change indicates the presence of starch.

• Add vinegar to the food sample, a color change to red indicates the presence of starch

• Mix the food sample with sugar, a sweet taste confirms the presence of starch

Explain how you would investigate the effect of temperature on the rate of reaction between sodium thiosulfate and hydrochloric acid.

• Using different concentrations of the chemicals

• Conducting the experiment in different locations

• Mixing the chemicals without measuring the time

• Conduct a controlled experiment varying the temperature while keeping other factors constant, measure the time it takes for the 'X' to disappear at each temperature, and repeat the experiment multiple times for accuracy.

Describe a method to identify the gases evolved during the electrolysis of water.

• Mix the gases together and observe the color change

• Heat the gases and observe the change in volume

• Collect the gases separately at the anode and cathode. Oxygen is identified by its ability to relight a glowing splint, while hydrogen burns with a 'pop' sound.

• Use a magnet to separate the gases based on their magnetic properties