CHEM 281 LAB EXAM QUESTIONS WITH CORRECT ANSWERS LATEST UPDATE 2026

CHEM 281 LAB EXAM QUESTIONS WITH CORRECT ANSWERS LATEST UPDATE 2026 separates impurities from a solid - Answers recrystallization recrystallization is achieved by dissolving the solid in a ___ solvent then _______ that solvent to allow the formation of crystals - Answers hot, cooling when choosing an adequate solvent for the solid to purify, it must dissolve the solid when it is ___ but not _____ - Answers hot, cold what is the role of activated charcoal in recrystallization - Answers absorbs impurities steps for cooling down recrystalization solution: 1. cool _______ flask down to room temperature 2. place in ____ _____ - Answers conical, ice bath in the recrystaliziation lab, what solvent was used - Answers methanol adding boiling stones to the flask ensures that the methanol boils more calmly and is less likely to _____ - Answers spill methanol's boiling point - Answers 65 before recrystallization can begin, the solution must be ______ to remove _______ _________ and associated impurities - Answers filtered, activated charcoal during filtration, if the liquid is not very hot, crystals will form in the _________ and the ________ - Answers funnel, filter what size must the filter be - Answers same as the funnel the solution should not be put in the ice bath if it is still hot because cooling too quickly might trap ______ in the _________ - Answers impurities, crystals what piece of equipment is used to separate napthalene crystals from methanol solvent - Answers suction filtration it is important to remove the methanol remaining in the sample before reweighing it because otherwise we will measure its _______ - Answers weight an impure substance will have a ______ melting point than a pure substance - Answers lower the lower the melting point in comparison to the pure substance, the _____ impurities the solid contains - Answers more these are used to distribute heat homogeneously in the tube during the melting point part of recrystallization - Answers capillary tubes the melting point apparatus measures the temperature at which the napthalene ____ _______ and when all napthalene is ______ - Answers starts melting, melted we shake the separatory funnel to _________ the contact surface of the two ________ - Answers increase, phases we vent the separation funnel to release a build up of _______ - Answers pressure before performing liquid liquid extraction with coffee, you must ______ the coffee first - Answers filter when the contact area between the two phases is increased, caffeine can transfer from the ________ phase to the _________ phase - Answers aqueous, organic we add dichloromethane to extract the caffeine because caffeine has a ________ relative _________ in dichloromethane than in water - Answers higher, solubility the organic layer is the _____ one - Answers lower after separating the organic phase from the aqueous phase, we must remove the ________ by heating the solution above the boiling point of DCM - Answers solvent the heating mantle should be placed on what side of the distillation apparatus - Answers left what is the first thing that you calculate when performing a distillation on a mixture - Answers mole percent of water the thermometer bulb should extend just _____ the sidearm connecting the condenser to the distillation head - Answers below the thermometer measures the temperature of the _____ that condenses in the __________ - Answers vapor, condenser water should flow into the _____ of the condenser - Answers bottom if you were to add water to the top of the condenser, the water would fall to the bottom and create an ____ _______ in the cooling jacket - Answers air pocket lowest curve on a boiling point composition diagram - Answers liquid composition line the liquid composition line tells you the _____ _______ of the compounds when they are in the liquid phase at a given temperature - Answers mole composition highest curve on a boiling point composition diagram - Answers vapor composition line simple distillation is only an effective technique to purify a mixture of liquids if they have __________ boiling points - Answers different in a simple distillation, the mixture is heated to ______, the ________ travel up the glassware until they hit the _______ reflux condenser, the vapors re-condense and are collected in a ______ ______ - Answers reflux, vapors, cold, collection flask