Chemistry II Past Paper - 27.10.2023 - PDF

Basic Laboratory Equipment Note: The noun 'equipment' is uncountable. Equipment does not have a plural form.  Basic Laboratory Equipment Spatulas are used to transfer samples or chemicals from their original containers to weighing paper, or containers for weighing. F...

Basic Laboratory Equipment Note: The noun 'equipment' is uncountable. Equipment does not have a plural form.  Basic Laboratory Equipment Spatulas are used to transfer samples or chemicals from their original containers to weighing paper, or containers for weighing. Flasks can be used for making solutions or sometimes volumetrically measuring chemicals, samples, solutions, etc. for chemical reactions or other processes such as mixing, heating, cooling, dissolving, precipitation, boiling (as in distillation), or analysis. Funnels are used to channel liquids or fine-grained chemicals (powders) into labware with a narrow neck or opening. When used with filter paper, filter funnels, can be used to remove fine particles from a liquid in a process called filtration. A pestle is a tool used to crush, mash or grind materials in a mortar. A buret is used to deliver solution in precisely-measured, variable volumes. A dropper is a device used to transfer small quantities of liquids.  Basic Laboratory Equipment An evaporating dish is used for the evaporation of solutions. A pipette is a laboratory instrument used to measure out or transfer small quantities of liquid, in volumes of milliliters (mL), microliters (μL). While beakers are used for transporting and mixing solutions, graduated cylinders are used to measure the volume of liquids. A crucible is a type of laboratory glassware used to burn, melt or mix solid chemical compounds over a burner. A crucible is a ceramic or metal container in which substances may be melted or subjected to very high temperatures. Test tubes are used to heat, hold and mix small amounts of liquid or solid chemicals during experiments. They have a round bottom and are made of borosilicate glass to withstand temperature changes and resist chemical reaction. The test tubes have transparent glass to allow monitoring and observation during an experiment.  An Example Experiment: Physical Separation Techniques In this experiment, you will separate a three-component mixture of sodium chloride, iron filings, and silicon dioxide into its individual components. Measuring the mass of the original mixture and measuring the masses of the pure components will allow you to calculate the percent by mass of each substance in the original mixture. Safety Safety goggles must be worn at all times during this and all chemistry experiments, from the very beginning to the very end of the time you spend in the laboratory. Disposal Dispose of the iron in the heavy metal waste container. You may rinse sodium chloride residues down the drain with water. Dispose of the sand you isolate from the mixture in the regular trash can. Cleanup At the end of the lab period, wipe down all your work surfaces with a damp sponge. Experimental Procedure 1. Obtain an unknown solid mixture and record its number. 2. Using a weighing bottle, determine the mass of your unknown solid mixture. A. Separation of Iron Filings Place the bar magnet inside a sandwich bag. While holding one end of the magnet, move the other end through the mixture. The iron filings will stick to the magnet. Shake gently to remove any trapped sand. It is not necessary to remove all the iron filings at one time. Gently lift the magnet with the iron filings and place the end with the filings inside a preweighed 100-mL beaker. Fold the plastic bag over the beaker. Carefully pull the magnet out of the bag, leaving the filings in the beaker. Repeat twice to remove the last traces of iron filings from the sand-salt mixture. Determine the mass of the 100-mL beaker with the iron filings. Calculate the mass of iron fillings in the mixture. B. Extraction of NaCl Weigh a 400 or 600 mL beaker together with a watch glass. Weigh a piece of filter paper. Add about 5 mL of distilled water to the NaCl- SiO2 mixture in an evaporating dish and stir gently for 1 minute. Filter the sand-salt solution through the weighed filter paper in a funnel into a weighed beaker. The solution that comes through the funnel should appear clear. Add 5 mL more distilled water to the evaporating dish to dislodge the remaining sand and pour this through the funnel. If all the sand is now gone from the evaporating dish, pour a fourth 5 mL portion of water directly onto the sand in the funnel. If any sand remains in the evaporating dish, pour the last portion of water into the dish to remove the rest of the sand, making sure all the water and sand go in the funnel. C. Drying of SiO2 Carefully place your wet filter paper cone with sand on a watch glass. There is no need to unwrap the cone. Place the watch glass in the laboratory drying oven. After about 30 minutes, the sand will be dry. Remove the watch glass, dried filter paper, and sand from the oven. Allow them to cool to room temperature and weigh the filter paper and sand on the same balance you used earlier to weigh the filter paper. Calculate the mass of SiO2 alone. D. Drying of NaCl While the SiO2 is in the drying oven, place the beaker containing the NaCl solution on a hot plate. Place the watch glass on top of the beaker. Heat the solution to evaporate the water. If the salt appears to be dry but there is still water on the beaker walls, continue heating until all the water is gone. Remove the beaker from the hot plate and let it cool to room temperature. Weigh the beaker, watch glass, and salt together on the same balance you used to weigh the beaker and watch glass. Subtract to find the mass of NaCl in the original mixture. You may rinse the solid NaCl residue down the drain. E. Percent by Mass Determine the percent by mass of each component on your mixture using the following formula: