Chen Lab 2

.pdf

School

University of Waterloo *

*We aren’t endorsed by this school

Course

121

Subject

Chemistry

Date

Dec 6, 2023

Type

pdf

Pages

Uploaded by DrFlyMaster964

Procedure: Sign out from the storeroom: 50 mL round bottom flask 500 mL vacuum flask Buchner funnel powder funnel thermometer Pick up from the side bench or cabinets: (*if not already at your bench) metal rod utility clamp 2 2 filter paper melting point tubes hot plate and cord* Mel Temp (melting point apparatus)* As soon as you arrive in the laboratory, set up a water bath, on a hot plate, using ~250 mL of deionized water in a 400 mL beaker. The reaction mixture will be heated in a water bath at 65-75 •C. monitor the temperature with a thermometer. Bring the water bath to the desired temperature quickly by heating @ 400 °C, then turn the temperature down. Try to find a setting on the hot plate which will maintain the water bath within this temperature range. Note that it is easy to cool down a water bath quickly by adding some cool DI water. Part 1: Synthesis On the top-loading balance, weigh ~3.0 g of p-aminophenol into a clean, dry 50 mL beaker. Record the actual mass ed, with correct significant digits, on your data sheet. Using the powder funnel (which has a wide neck, signed out from the storeroom), add the p-aminophenol to the 50 mL round bottom flask. Measure 10 mL of deionized water using a 25 mL graduated cylinder, use this water to rinse the beaker and funnel and add it to the round bottom flask When the water bath has reached the desired temperature range, attach a utility clamp to the neck of the round bottom flask, and clamp it in place in the water bath. Heat the mixture in the water bath for 5 minutes while stirring continuously with a glass rod. Some p-aminophenol will dissolve at this time; the rest will dissolve upon the addition of acetic anhydride. In the fume hood, measure 4.0 mL of pure acetic anhydride with a dry 10 mL graduated cylinder. Back at your bench, quickly pour the acetic anhydride into the round bottom flask. Continue heating and stirring the reaction mixture for 5 more minutes. All of the p-aminophenol should dissolve during this step, and you should observe a clear solution when it does. Remember that observations need to be recorded on your data sheet throughout the experiment.

Be sure not note when you next see solid form in the flask. Remove the round bottom flask from the heated water bath and continue to mix the reaction at room temperature for 5-10 more minutes (stir with a glass rod, or simply swirl the flask gently). Next, place the flask in an ice-water bath (mix ice and water in a 250 mL, or larger, beaker) to cool: DO NOT STIR! The solid product should precipitate from solution. If no precipitate forms after 10 minutes, scratch the bottom of the flask with a glass rod, to induce precipitation. Cool for another ~5 minutes after scratching. Collect the crude product using vacuum filtration. Use a small amount of cold deionized water to assist in the transfer of the solid to the Buchner funnel. Keep the solid under vacuum for ~5 minutes to dry. Load a small portion of this crude solid into a melting point tube and set aside for melting point determination once both crude and purified products are isolated. (Your instructor will demonstrate how during the pre-lab talk.) After filtration, keep the solid and discard the filtrate (liquid) into the aqueous waste container. Part 2: Recrystallization The crude product will now be purified by recrystallization using DI water as the solvent. Using a top-loading balance, weigh a clean and dry 125 mL Erlenmeyer flask. Record this mass on your data sheet. Back at your lab bench, transfer the crude product to the weighed Erlenmeyer flask. (Do not transfer chemicals at the balances.) Return to the top-loading balance and reweigh the flask plus product. Record this mass on your data sheet. Calculate the mass of crude product and record this value on your data sheet. Add 10.0 mL of deionized water per gram of crude product to the Erlenmeyer flask. Record the volume of water added on your data sheet. Heat the mixture in the flask on a hot plate until all the product dissolves, swirl the mixture frequently to ensure even heating. The solution temperature will need to reach 85-90 °C for the crude product to dissolve. Once the solid has dissolved, remove the flask from the hotplate and let the flask cool on the lab bench, undisturbed, to room temperature (~5 minutes). Turn off and unplug the hotplate. After 5 minutes, carefully move the flask to an ice-water bath for ~10 minutes, do not disturb the flask while it cools. If after 10 minutes the product has not recrystallized out of solution scratch the bottom of the flask with a glass rod to induce crystallization, cool for 5 more minutes. Recover the pure product by vacuum filtration using a small amount of cold deionized water to assist in the transfer of the solid to the Buchner funnel. Keep the solid under vacuum for 5 minutes to dry. Weigh the purified product using the top-loading balance. Record the mass of purified product on your data sheet. Load a sample of purified product into a melting point tube for melting point determination. Using a MelTemp melting point apparatus from the side bench, take a melting point of both the crude and purified products. The MelTemp will accommodate up to three melting point tubes, do both melting points at the same time. Record the melting temperature (or temperature range) for both the crude and purified products on your data sheet.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version