CHEM-UA 225 Chapter : Recrytallization

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21 Oct 2014

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These changes should not be interpreted as the beginning of the melting process. Includes melting point, boiling point, index of refraction, density, specific rotation, and solubility. 114: melting point - the temperature at which the liquid and solid phases of a substance exist in equilibrium with one another without change of temperature a. If a sample lies more to one side of the eutectic point than the other, it may be considered impure in relation to the side it"s on. Trap should be a heavy-walled bottle or second vacuum filter flask wrapped with electrical or duct tape. If a filter flask is used, it should be equipped with a two-holed stopper with its sidearm attached to the first filter flask with heavy-walled tubing. If sudden backup occurs, the vacuum should be released immediately so that the trap doesn"t fill completely with water.

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Procedure Reaction 1: Dissolving the Copper 1. Obtain a clean, dry, glass centrifuge tube. 2. Place a piece of copper wire in a weighing paper, determine the mass of the wire and place it in the centrifuge tube. The copper wire should weigh less than 0.0200 grams. 3. In a fume hood, add seven drops of concentrated nitric acid to the reaction tube so that the copper metal dissolves completely. Describe your observations in the lab report. (Caution, Concentrated nitric acid and nitrogen dioxide are very corrosive. Either will turn your skin yellow on contact. Do not leave any spills on the lab bench or in the fume hood.) 4. When the copper has dissolved, add seven drops of distilled water to the tube. Reaction 2: Preparation of Copper(II) Hydroxide 1. Add 15 drops of 3.0 M aqueous sodium hydroxide to the tube. Make sure that the reactants are well mixed. Shake the tube carefully or gently flick the bottom of the tube with your finger. Remember that the contents of the tube may still be corrosive. 2. Add a second 15 drops of NaOH(aq), mix well, and record your observations. If you have two layers at this point it means that you have not mixed the solution well enough. 3. Centrifuge the reaction mixture. 4. The liquid at the top of the centrifuged mixture is called the supernatant while the solid is called a precipitate. Before separating the supernatant from the precipitate it is necessary to ensure that all of the copper(II) hydroxide has been precipitated. The supernatant should be clear and colorless indicating the absence of any Cu+2 ions in the solution. It should also be basic due to an excess of OH- ions. Using a clean glass stirring rod, transfer a drop of the supernatant onto a piece of red litmus paper. If the litmus paper turns blue then the solution is basic and enough NaOH has been added. If the paper does not turn blue, add more NaOH, mix well, recentrifuge, and repeat the litmus paper test until the paper does turn blue. 5. An efficient separation of supernatants and precipitates is key to obtaining a good final yield of copper. The supernatant liquid can be separated from the precipitate by expelling the air from the bulb of a Pasteur pipet, inserting the tip of the pipet into the supernatant, then gently sucking the supernatant into the pipet. If you expel air or liquid into the precipitate with the pipet, you will stir up the precipitate and will have to repeat the centrifugation step. Remove as much liquid as possible and discard it in the waste container provided on the instructorâs cart. It is better to leave a small amount of supernatant liquid than to remove some of the copper(II) hydroxide precipitate. Reaction 3: Formation of Copper(II) Oxide 1. Set up a hot water bath by placing a beaker of water on a hotplate, placing an iron ring around the beaker, and heating the water to boiling. 2. Place the centrifuge tube containing the copper(II) hydroxide into the boiling water. Carefully hold the tube with a test tube clamp so that it doesnât get water into it. Record your observations. Reaction 4: Formation of Copper(II) Sulfate 1. Add 20 drops of 3.0 M H2SO4 to the solid in the centrifuge tube. Stir carefully to ensure that the copper(II) oxide dissolves completely. Complete dissolution of the mixture will require thorough mixing and possibly heating of the solution. 2. Obtain the mass of a small, clean, glass test tube as accurately as possible. 3. Transfer the liquid from the centrifuge tube into the test tube. Rinse the centrifuge carefully with 1.0 mL of distilled water and transfer the rinse into the test tube containing your sample. 4. Record your observations on the data sheet. Reaction 5: Formation of Copper Metal 1. Add a small quantity of zinc powder to the sample solution. Continue adding zinc in small quantities until the solution loses the blue copper(II) color. Any excess zinc added will need to be removed so donât add it too quickly or in large quantities. When the solution has turned colorless, add several drops of 3.0 M H2SO4 to the tube to dissolve any left over zinc. You can tell that the zinc has dissolved when addition of sulfuric acid does not generate bubbles. 2. Allow the copper metal to sink to the bottom of the tube and carefully remove the supernatant liquid using a Pasteur pipet. 3. Wash the red-brown copper metal in the tube with 1.0 mL of water. Allow the copper metal to settle to the bottom and remove the excess water. Repeat this rinsing process two more times. 4. Describe your observations on the data sheet. Drying the copper metal 1. After removing as much of the third rinse water as possible you are ready to dry the metal. This must be done carefully in a cool Bunsen Burner flame. If the tube is heated too quickly there is a risk of ejecting the contents of the tube as the water boils. Also, if the flame is too hot you may convert the copper metal back into black copper(II) oxide. The objective is to drive the water from the tube as steam. Make sure that as water condenses on the walls of the tube that you continue to heat until all of the water if gone from the tube. 2. Once all of the water is removed from the tube, cool the tube and its contents then determine the mass of copper by weighing the tube and subtracting the tube + copper weight from the weight of the empty tube (Reaction 4 step 2). If the mass of copper is higher than the original mass of the copper wire it either contains water or zinc or has been converted to copper(II) oxide. Excess water can be removed by reheating the tube and reweighing to constant mass. Excess zinc requires addition of sulfuric acid followed by re-rinsing with water and re-drying. Chemistry 1215 Experiment 9 Lab Report Name ______________________________ Data Sheet Mass of copper wire _______________ Mass of clean, dry test tube _______________ Mass of test tube plus copper _______________ Mass of final copper sample _______________ Percent recovery of copper. Show all calculations. Observations 1. Describe your observations for Reaction 1 including colors, gases formed, etc. 2. Describe your observations for Reaction 2 including colors, gases formed, etc. 3. Describe your observations for Reaction 3 including colors, gases formed, etc. Estimate the temperature of the decomposition of Copper(II) hydroxide. 4. Describe your observations for Reaction 4 including colors, gases formed, etc. 5. Describe your observations for Reaction 5 including colors, gases formed, etc. Write a brief discussion of your results including a statement of the final percent recovery of copper and a discussion of reasons why the recovery differs from 100%. Chemistry 1215, Experiment #9; Copper and its compounds, Pre-lab Name ____________________________________ 1. Write a balanced chemical equation including phase labels for the reaction between aqueous copper (II) nitrate and aqueous sodium hydroxide. 2. Nitrogen monoxide (NO) and nitrogen dioxide (NO2) are toxic, corrosive gases that significantly lower blood pressure when inhaled. How are these gases produced in todayâs experiment? What should you do to protect yourself against their toxicity? 3. Iron reacts with oxygen from the atmosphere to produce iron (III) oxide, also known as rust (Fe2O3). What chemical species is oxidized in this reaction? What is the reducing agent? Jaffrey Zagnut couldnât find any nitric acid so he tried to dissolve his copper sample in hydrochloric acid instead. Unfortunately his copper wouldnât dissolve in HCl. Why will copper dissolve in nitric acid but not in hydrochloric acid (after all, HCl is a stronger acid than HNO3). Chemistry 1215, Experiment #9; Copper and its compounds, Post-lab Name ____________________________________ 1. Copper (II) hydroxide is converted into copper (II) oxide by heating the test tube containing Cu(OH)2 in a hot water bath. Is it necessary to use distilled water in this water bath? Why or why not? 2. Copper metal doesnât ârustâ in the presence of oxygen at room temperature. However, it will react with O2 at elevated temperatures. Write a balanced chemical equation describing the formation of copper (II) oxide when copper metal is heated in air. 3. When zinc is dissolved in sulfuric acid a gas is produced. What is the chemical identity of this gas? How is it produced? 4. Jaffrey Zagnut started with a 0.032 g sample of copper which he took through the series of reactions described in this experiment. At the end of the experiment he obtained 0.038 g of a black product. What was his percent yield? What is the most likely source of the error in his experiment? (Hint: consider question 2 above)

Part 1: Separation of Iron filings

Mass a watchglass and record
Obtain a Kimwipe tissue from the top of the benches and a rodmagnet
Wrap the Kimwipe tissue around the magnetic end, holding thetissue tight to the rod magnet.
Swirl the Kimwipe in your mixture. Knock off excess sand beforemoving on to step 5
Carefully over the watch glass remove the Kimwipe tissue fromthe magnet so the iron falls on the the watch glass
Repeat steps 4 and 5 two more times, make sure you record howsuccessful this separation was ï¿½ does the evaporating dish containonly iron?
Mass the watchglass and the collected iron.
Dispose of the iron in the hood.

Part 2: Separation of N

Mass a clean, dry, evaporating dish.
Pour the leftover mixture from step 1 into the evaporating dishand mass.
Place the evaporating dish on a hot plate in the hood.
Gently and slowly heat the mixture until the white fumes cease.Be patient. Depending on the amount of ammonium chloride in yoursample, this could take quite a while. A half our would not beunheard of.
Stir the mixture frequently to facilitate the sublimation ofthe ammonium chloride. This is crucial in order to obtain goodresults. (Use crucible tongs to hold onto the dish so it doesnï¿½tmove as much)
After the white fumes disappear, turn off the hot plate andremove the evaporating dish with crucible tongs and let it cool inthe hood.
When the evaporating dish is cooled, mass the left overmaterial and the evaporating dish.

Part 3: Determining the amount of NaCl.

Measure 10 mL of distilled water in a graduated cylinder.Slowly add the water to the mixture in the evaporating dish whilecontinuously stirring with a clean, glass stirring rod. Afteradding all of the water, stir for 2 min more.
Assemble the gravity filtration apparatus shown in Figure1.
Fold a piece of filter paper as shown in Figure 2. Open up thepaper cone, and place it in the filtering funnel.

Position a beaker under the funnel, making sure that the funnelstem is touching the inside wall of the beaker. Pour as much of thesupernatant liquid as possible from the evaporating dish intofunnel. Collect the filtrate in the beaker.
Transfer the solid remaining in the evaporating dish into thefunnel, using a stream of distilled water from a wash bottle, asshown in Figure 3.
Re mass the watchglass from Part 1 and record this mass.
Pour the filtrate in the beaker into the evaporating dish
Place the evaporating dish containing the filtrate on a hotplate. Begin heating the solution.
While the solution is heating to boiling, move onto Part 4

Carefully remove the filter paper and residue from the funnel.Place the paper and residue onto the watchglass.
Place the watchglass with the filter paper and sand on top ofthe boiling salt solution to dry the sand
Keep the salt water boiling, until there is just a little bitof water left, or popping sounds are heard, then turn off the hotplate, and allow the heat from the hot plate to finish evaporatingand drying your salt.
Allow the evaporating dish and its contents to cool to roomtemperature.
Obtain another watch glass and mass.
Transfer the dried sand and filter paper from original watchglass (caution, salt has spattered onto this watch glass, so donï¿½tknock any off, that is product you will need) onto the new cleanmassed watch glass. Replace the original watch glass onto thecooling evaporation dish
Mass the new watch glass, sand and filter paper all together.Discard filter paper and sand into garbage. Observe how pure yoursand looks.
After evaporating dish has cooled, determine the mass of theevaporating dish, watch glass plus NaCl. Record this mass. Then,discard the NaCl as directed. Wash evaporating dish and watch glassto dissolve the salt.
Observe how pure your salt looks.

Result and Discussion: Separation Lab

Substance	Grams recovered	% mass
Fe
NH4Cl
NaCl
SIO2

Overall percentRecovery:

A) Explain what steps(s) youcould have improved (and how) to help your percentrecovery.

b) Write a paragraph about thelab include briefly what was done, your result, were you correctand possible experimental errors- do not state human measurementerrors as errors. Be Specific, what specific human errors occurred,what measurement errors occurred, what process in the experimentcould errors have occurred.

used 0.113g of CuCl, 1.0ml 95% ethanol, 1.0ml 2-methyl-3butyn-2-ol, 0.51ml NH4OH, 0.50ml concentrated hydrochloric acid, 2.5ml NaCl, 5ml MTBE, 2.7ml NaCl

Organic Chemistry I Lab-Chem. 322 A Greener Glaser II: Oxidative Coupling of Alkynes: 2,7-Dimethyl-3,5-octadiyn-2,7-diol er Glaser Il: Oxidative Coupling of Alkynes: 2,7-Dimethyl-3,5-octadiyn-27-diol ã¢q pa25 mL filtering flask with a magnetic stirring bar and arm and secured with a small rubber band: (Practice placing a 19/22 white rubber septum tne tlask, folding the top of the septun down and over the lip of the fask Add 0.1g concentrated NH OH. Place a 19/22 White rubber septum over the top of the fask, purge Clamp the flask 1-2 ãabo eastr plate and let the o a small balloon attached to the side 0.1g of CuC catlalyst to the flask Tollowed by 10 mt 95% ethanol 1.0 mL- of 2-methy-3butyn-2-ol, and 0.5mf ygen for1 minute, then fill the baltoon untit mosty inflated- (Your instructor wil you with this procedure. ur. A greenish-blue or blue color should begin to develop almost imme diately. If the batoon deflates substantially, refill it with more oxygen. Stir for 1 hour to mix the slurry well at and every few minutes swirl the flask . Open the reaction flask, cool if warm, and add 0.5 m L of concentrated hydrochloric acid to neutralize the NH OH and keep the copper compounds in solution. Th colo a few more drops of acid. Add 2.5 mL of saturated NaÄI solution to precipitate Pasteur pipette, until all n. The color will change from b in color ater mixing thoroughly, add or yellow, If the mi the diol and stir the sion that results Add MTBE (methyl t-butyl ether) in 2mL increments, mixing well using a organic solids dissolve (add up to 6 mL MTBE, but no more). [Note: If a te precipitate forms, add additional water to the mixture to dissolve it. All solids should be dissolved at this point. Fransfer the mixture to a centrifuge tube and separete the two layers by removing the bottom ayer using a Pasteur pipette: Add-about 3mL of saturated NaCl solution to the organic layer and mix well using the pipette. Allow the layers to separate and again remove the bottom layer. The organic layer-shoutd be clear and cotortess or light yellow (IF NOTwash again with another 3 ml of saturated aqueous NaCt and separate the layers).Transfer the organic layer to a dry 16x100-mm-test tube and dry the solution with anhydrous sodium sulfate (use approximately the amount you would need to cover a dime) for at least 10 min: The drying agent should remain granular in appearance. Using a Pasteur pipette, transfer the organic layer to a 10mt Erlenmeyer flask teaving the drying agent behind Add-Norit activated charcoat (use approximately the amount you would need to cover a dime and boil the with a small cotton plug and about 1 cm of Celite. Use compressed air and a dry condenser hose to speed the filtration if necessary mixture gently for 2 minutes Filter the cooled solution through a fiter pipet fitted Rapidly boil off all the solvent on a hot plate set to -80Â°C in the hood. When the boiling, remove it from the heat. You should have a solid residue at this point. At your bench remove the last traces of solvent by connecting the flask to a vacuum trap apparatus using the thermometer adapter and a short glass tube solution stops At your bench, recrystallize the product from a minimal amount of boiling toluene. You will need to use a heating mantle to generate sufficient heat to boil toluene. Cool the solution slowly to room temperature, then cool on ice. Isolate the product using the Hirsch funnel rinsing the product with a small amount (ca. 0.5-1.0 mL) of ice-cold toluene. Allow the product to air dry in a sample envelop in your drawer until next week, and then determine the mp and yield. Submit your product (label as Diyne' with your 1 initial last name, w, and mp) to your instructor The aqueous filtrate from the reaction mixture should be placed in the acidic aqueous waste. The filtrates from recrystallization of the diol should be placed in the or Clean up: ganic non-halogenated waste

CHEM-UA 225 Chapter : Recrytallization

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