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Chemistry Lab Final Exam.pptx - SKELETON GUIDE

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University of Waterloo
BIOL 110

CHEMISTRY FINAL EXAM Notes General • Know the safety information from the introduction of your lab manual. • Pay attention, ask more questions if not understood, don’t perform unattended and unrequired experiments, bench-tops must be free of backpacks, stools, etc. • Protective clothing: Safety goggles, Footwear, lab coats • Long hair tied up. • Food & Drink prohibited. • First aid: • For acid, alkali or other chemical splashed on skin, cuts, abrasions or burns. • Chemicals on skin: Wash immediately, health services if immediate • Chemicals in eye: Emergency eye wash station, health services • Cuts, abrasions & burns: Report to TA; for all as well General Cont’D • Fire & Explosions • Stop, drop, roll • Locate nearest exit • Fire extinguishers • Class A fires: ordinary combustible materials (paper, wood, plastics) • Class B fires: flammable/combustible liquids (gasoline, grease, oil, solvents) • Class C fires: electrical equipment (appliances, circuit breakers, outlets) • To operate fire extinguisher (PASS) • Pull the pin or locking device. • Aim low, at the base of the fire. • Squeeze the handle. • Sweep slowly and evenly across the base of the fire. • Safety with chemicals and glassware • MSDS sheets, proper disposal, labelling, mercury spills, rubber bulb, stoppers, etc General Cont’D • Review Appendix C: Laboratory techniques for all techniques used this term. • Qualitative Techniques • Handle with attitudes of cleanliness, neatness, orderliness and respect for the equipment. • Gross Errors of Technique • Caused by not paying attention. • Some are due to: • Spilling a solution of a sample – collision • Splashing sample solution our of the container – addition of water • Recording weight incorrectly. • Neglecting to cover a beaker or flask & allowing impurities to fall into the sample. Reading the start volume of burette’s. • Neglecting labelling/identify – confusing containers. • Weighing an object diff. temp than the analytical balance. General Cont’D • Measurement of Mass • Mass: measure of the quanitity of matter. • Analytical balance: measures mass by comparing mass of an object with the mass of a set of “weights” which have been universally accepted for this purpose. • Weight vs. Mass • Weight: the force of the earth’s attraction on an object. • Weight = mass x acceleration of gravity. • Accuracy & Precision • The “true” values. – But not always obtainable. • Precision: A measure of the reproducibility of an experiment & can be quantitatively expressed as an average or standard deviation. • It’s not necessarily a precise measurement as many errors in the measuring techniques can constant. General Cont’D • Weighing Replicate Samples of a Solid • Initial weighting: • A measure of the clean, dry beaker/flask/etc = weighing beaker • Analytical by difference: • Take weighing beaker & 3 other flasks. • Use paper to lift beakers. • While weighing to desired weight, pour/tap a little bit into each of the flask so that they all have the equal amount. • Advantages: • The advantage of weighing the weighing beaker rather than the revieving flasks are: • A) Only n+1 weighings are required to prepare n samples: ie. 4 weighings for 3 samples. • B) The titrating flasks need not be dry, only the weighing beaker. • It don’t matter if exactly the same amount is weighed into each flask. General Cont’D • Use of a Burette in a Standardization Titration • A burette used for accurately measuring volumes of a solution. The key operations in using a burette are: • A) Reading the meniscus level • Proper rinsing • Proper filling without spillage • Removing air from the tip • Touching off droplets from the tip • Rinsing the burette • Not dirty, small funnel, rinse around 3 times. • Filling the burette • Use small funnel to fill to near the zero with desired solution. Wipe. • Initial reading of the burette • Pour above 0, pour out from bottom until the meniscus reaches 0. General Cont’D Continued: Use of A Burette In a Standardization Titration • Titration • 2/3 cm into the titration flask. Rate of drops decreases.
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