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13 Dec 2019

Students are attempting to construct a battery in the laboratorythat will light up a light bulb. Compare the following listsprepared by students and determine which student will not be ableto successfully build a "battery" that will light up the bulb.

Select one:

a. Student 1

large beaker

strip of aluminum metal

strip of silver metal

sodium nitrate solution

aluminum nitrate solution

a porous membrane

a length of copper wire

light bulb

b. Student 2

2 beakers

strip of magnesium metal

strip of nickel metal

magnesium chloride solution

nickel(II) chloride solution

potassium chloride salt bridge

a length of copper wire

light bulb

c. Student 3

2 beakers

strip of zinc metal

strip of gold metal

gold(III) chloride solution

zinc(II) chloride solution

sodium chloride salt bridge

a length of copper wire

light bulb

d. Student 4

1 large beaker

strip of cadmium metal

strip of copper metal

copper(II) chloride solution

cadmium chloride solution

sodium chloride solution

a porous membrane

a length of copper wire

light bulb

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Deanna HettingerLv2

17 Dec 2019

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OBJECTIVE:

In this lab, you will produce several different voltaic cells, measure the total voltage, and determine the corresponding half-cells and total potentials. A copper electrode and a copper gluconate electrolyte solution will be used in every system, and four additional half-cells with different metals and salts will be run against it to compare the half-cells and total overall voltage. The salt bridge, consisting of filter paper and potassium chloride, connects the two cells.

PROCEDURE

Put on your goggles and lab apron.

Label five clean, dry 100 mL beakers as copper gluconate, tin sulfate, aluminum sulfate, iron sulfate, and zinc

sulfate.

Using a clean, dry 100 mL graduated cylinder (and pipette if needed), measure and pour 25.0 mL of each

solution into the corresponding beaker. Be sure to thoroughly rinse the graduated cylinder with dH2O before measuring out a new solution. Some of your bottles of solution may need shaken up before using to re- dissolve anything that has settled out. If shaking doesnât completely work, use a clean, dry glass stirring rod to help break up and dissolve. Mix thoroughly. Just be sure to clean the stir rod before moving it to a different solution bottle.

Lightly sand the provided metal strips of copper, tin, aluminum, iron, and zinc down with sand paper to remove the oxidized layer. When finished, wipe off any debris. Set the strips aside. Be sure you have sanded these well to ensure reaction.

Use scissors to cut the filter paper into five strips. Each strip should measure about 20 mm (2 cm) x 150 mm (15 cm).

Note: When your electrochemical cell apparatus is set-up, each strip should be long enough to connect the electrolyte solutions in the two adjacent beakers (half-cells). The strips may look short now, but after they soak, you will see that are the proper length. See pic below.

Using a clean, dry 100 mL graduated cylinder, measure and pour 25.0 mL of potassium chloride solution into a 100 mL beaker. Place the filter paper strips into the beaker. Allow the strips to soak for approximately 5 minutes. This process creates the salt bridge. Be sure all papers are in contact with KCl and get soaked.

Place the metal copper strip in the copper gluconate beaker, allowing it to lean against the side of the beaker.

Repeat Step 7 for each of the metal strips and the corresponding beakers (see pic below).

Place one of the potassium chloride soaked filter papers between the copper gluconate solution and the tin

sulfate solution so that the filter paper is immersed in both solutions simultaneously. The KCl strip must be touching both solutions (itâs OK for the strip to cling to the wall of each beaker, so long as it is touching both solutions)! Pick up the strip by the middle, and drain excess solution by touching the ends to a paper towel. Position the paper strip salt bridge so that it makes contact with both solutions, but is not touching the electrodes.

Assemble the 7-Function Multi-Meter by firmly pressing the positive (red) Test Lead into the V?mA (center) jack. Press the negative (black) Test Lead into the COM (bottom) jack. Rotate the red, center dial until it is pointing towards the DCV 2000 m position (Hint: this position is similar to the northwest position on a compassâsee pic below). 2000 m is equal to 2 volts. That means your read out is now in mV, so you will have to divide the readout by 1,000 when recording your data in V. For example, in the picture below, my readout of 980 mV would be 0.980 V. Turn the multi-meter on.

Touch the red multi-meter probe to the top of the copper strip, and the black multi-meter probe to the top of the tin strip. This works best when you press lightly down on the top edge of the metal strip with the side of the probe, as this creates more constant contact and less fluctuation movement. See pic below. If you happen to have a set of alligator clips to connect the probes to the metal, that would work even better.

Note: The red probe should be placed on copper for all of the half-cell apparatuses. The black probe should be placed on the remaining metals.

Note: Alternatively, you can bend the metal strips to rest over the edge of the beaker, and to give a flat surface that makes it easier to rest the probes:

Record the voltage differential created between the two half-cell in Table 1 (see below). Watch the voltage for a few seconds and then take a reading. Some readings stabilize quickly, others will drift for as long as you want to watch. (Swirling the solution with the electrode can also change the reading.) Typically, waiting a few seconds after connecting the cell yields the most reliable reading.

Take a picture of your voltaic cell. This will be a little tricky since you have to hold the probes, but try to get someone to help. Otherwise, do the best you can. The digital readout on the multimeter must be visible for each sample, and both half cells must be visible and clearly labeled. Your face must be visible in the picture also, as well as a label with your name/student ID, the lab title, and the date. Unless all fourâyour face, name/ID, the lab title, and the date are clear, you will not receive credit. Save this picture, and combine all four voltaic cells (Sn, Al, Fe, Zn) into a single PDF document in order to submit it in the Lab 14 Assignment.

Discard the salt bridge, and repeat Steps 9 -13 three more times using the aluminum sulfate solution, iron sulfate solution, and the zinc sulfate solution. Each solution should be paired with the copper gluconate solution, placing the red probe of the volt meter on the copper each time. A new salt-bridge should be used for each electrochemical cell. Record your data in Table 1 (see below).

Wash your glassware (and plasticware) with warm water and soap. To minimize spotting and mineral contamination, it is best to do a final rinse with dH2O. Dry your glassware (or leave set to dry) and put it away. All chemical solutions used in this lab can now be safely washed down the sink, and solid metals can be thrown away or recycled. Clean up your lab and put away your materials.

RESULTS

Make a data table in either Word or Excel that shows the multi-meter voltage measurements (V), experimental half-cell potential using copper electrode as the standard, the theoretical half-cell voltage, percent error, the half-cell and net cell reactions, and free energy (?G). Your table should look something like the one on page 6 of this document. Also see the description below the sample table for help in determining all of these values. Make sure that the calculation sections shown below are included within your Table 1 document as well.

Save your Table 1 as a PDF file to be submitted with the Lab 14 Assignment. Be sure your document includes your name/student ID, lab title, and date. Unless all threeâyour name/student ID, the lab title, and the date are on the document and legible, you will not receive credit. All columns and values must be clearly labeled.

You should have = 1 PDF of a pic of you and your 4 electrochemical cells being measured (Step 13) + (Steps 16-17). All pictures, tables, and labels must be clear and properly labeled or they will not receive credit.

Question:

You probably observed the cell voltage change slightly while you were observing it. Explain what is occurring at the electrode that causes the observed voltage to change?

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)

You are asked to construct a voltaic cell that would simulate an alkaline battery by providing an electrical output of 1.50 VV at the beginning of its discharge. After you complete it, your voltaic cell will be used to power an external device that draws a constant current of 0.50 AA (amperes) for 2.0 hh. You are given the following supplies: electrodes of each transition metal from manganese to zinc; the chloride salts of the +2 transition metal ions from Mn2+Mn2+ to Zn2+Zn2+ (MnCl2MnCl2, FeCl2FeCl2, CoCl2CoCl2, NiCl2NiCl2, CuCl2CuCl2, and ZnCl2ZnCl2); two 100 mLmL beakers; a salt bridge; a voltmeter; and wires to make electrical connections between the electrodes and the voltmeter. The standard reduction potentials for the divalent metal ions are as follows: Half-reactionMn2+(aq)Fe2+(aq)Co2+(aq)Ni2+(aq)Cu2+(aq)Zn2+(aq)++++++2e−2e−2e−2e−2e−2e−→→→→→→Mn(s)Fe(s)Co(s)Ni(s)Cu(s)Zn(s)E∘(V)−1.18−0.44−0.28−0.250.34−0.76 Since you were tasked with constructing a cell that produces a potential of 1.50 VV, you decide to fine tune your concentrations to minimize the error. If you used the same concentration for each electrolyte, your voltaic cell would produce a potential of 1.52 VV. Therefore, you should adjust the concentration ratio that would lower your cell potential by 0.02 VV. You and a fellow researcher decide that you should prepare two 100 mLmL solutions for the voltaic cell. Your fellow researcher already prepared one of the electrolyte solutions for you: 0.228 MM CuCl2 CuCl2. At what concentration should you prepare the MnCl2MnCl2 solution such that your initial voltaic cell potential is 1.50 VV? Assume that the temperature is consistently 25 ∘C∘C. If the battery is permitted to discharge for a period of two hours at a constant current of 0.50 AA, what will be the concentration of the manganese(II) ion in the anode electrolyte solution at the end of the discharge? Similarly, what will be the concentration of the copper(II) ion in the cathode electrolyte solution at the end of the discharge? Given the nature of how a cell is constructed, you would usually deplete the ions at the cathode before completely oxidizing the anode (since the latter would break the circuit). This is because the complete oxidation of the anode would likely only occur if you were using an extremely thin wire of the metal. In this case, let us assume you constructed the voltaic cell using sufficiently sized rods for each metal. This means that the total time you can run your cell will depend on the initial copper ion concentration. Calculate the maximum run time for your voltaic cell if it runs at 0.5 AA and your initial concentration of CuCl2(aq)CuCl2(aq) was 0.228 M'