:Preparation of Iron (II) acetate and iron (III) acetate In this experiment, you

Question

:Preparation of Iron (II) acetate and iron (III) acetate In this experiment, you will perform and observe an oxidation-reduction reaction. LAB SAFETY: Both the matches and the Sterno® can cause fire or burns to skin, clothing, or lab materials if the flame comes into contact with them. Do not stick any body part, loose clothing, or other flammable items in or near the flame. Be sure you have your safety glasses on and never leave any burning fuel unattended!! Do this exercise in a well-ventilated area and have a fire extinguisher nearby. Procedure Part 1: Preparation of Iron (II) Acetate 1. Use a 100 mL graduated cylinder to measure and pour 150 mL of acetic acid into a 500 mL glass beaker. 2. Place a weigh boat on the scale. Press the button on the right hand side (0/T). Your scale should now read 0.0g. 3. Weigh out 1.0 g of steel wool. Then transfer the steel wool into the 500 mL glass beaker with the acetic acid. 4. Choose an area that is well-ventilated (yet not windy) and place your Sterno® cooking fuel can on a flat, heat resistant surface. 5. Thoroughly read all of the directions on your Sterno® cooking fuel can and then use your metal spatula to pry open the lid. Put the lid aside being careful not to touch any of the contents. If you accidently touch the contents wash your hands before you proceed with the experiment. 6. Use your metal spatula to slide the Sterno® cooking fuel can under the wire mesh stand. 7. Carefully place your 500 mL beaker with the acetic acid and steel wool inside on top of the wire mesh stand. 8. Touch a lit match to the Sterno® contents and drop the match into the contents. The contents will flame up immediately. Under bright lights you may not be able to see the flame but know that it is there. 9. Bring the acetic acid plus steel wool mixture to a boil and evaporate off 50 mL. This is the process to produce a solution of iron (II) acetate and should take approximately 30 to 45 minutes. 10. When the acetic acid plus steel wool mixture is down to the 100 mL mark on the 500 mL beaker, use the insulated glove to place the hot flask on an hot pad to cool. Do not place the hot flask directly on the counter because it can crack the glass! 11. Extinguish your Sterno® cooking fuel can by placing the cover on top of the can. Do not blow out the flame. Once the can is cooled (look at the temperature indicator on the label) snuggly fit the cover onto the can and store it in a safe place away from heat or flames. 12. Allow your solution of iron(II) acetate to cool down. This should take approximately two to five minutes. 13. Observe and record the color of the iron(II) acetate solution in Table 3. 14. Obtain a piece of round filter paper, a funnel and clean, dry glass 250 mL Erlenmeyer flask. 15. Prepare a filtering funnel as shown in Figure 3. Fold a piece of filter paper in half twice to make a quarters, and place the paper in the funnel so that three quarters are open on one side and one quarter is on the opposite side. Seat the filter paper into the funnel by moistening the paper with a small amount of water. 16. Insert the filter paper into the funnel and place the funnel into the mouth of the 250 mL Erlenmeyer flask. 17. Filter the iron(II) acetate solution into the 250 mL Erlenmeyer flask, leaving the steel wool in the funnel and place the 500 mL beaker aside. 18. Clean and dry your 500 mL beaker. Part 2: Oxidation of Fe2+ to Fe3+ 1. Rinse your 100 mL graduated cylinder thoroughly with water. Dry your graduated cylinder with a paper towel. 2. While you are waiting for the iron(II) acetate to finish filtering measure and pour 150 mL of 3% hydrogen peroxide into the clean dry 500 mL beaker. i. Hint: Use your clean dry 100 mL graduated cylinder to measure 50 mL of 3% hydrogen peroxide and pour it into the clean dry 500 mL beaker. Use the 100 mL graduated cylinder to measure 100 mL of 3% hydrogen peroxide and pour it into the 500 mL beaker. Your beaker should now contain a total of 150 mL of 3% hydrogen peroxide. 3. Place a weigh boat on the scale. Press the button on the right hand side (0/T). Your scale should now read 0.0g. 4. Use your metal spatula to weigh out 3 g of cream of tarter into your weigh boat. 5. Transfer your 3 g of cream of tartar into the 500 mL beaker which contains the 150 mL of 3% hydrogen peroxide solution. 6. Thoroughly stir the solution with the glass stir rod until the cream of tartar is evenly distributed throughout the hydrogen peroxide. 7. Remove the funnel from the Erlenmeyer flask and throw the filter paper with the steel wool into the trash and rinse out your funnel. 8. Thoroughly rinse your 100 mL graduated cylinder with water. Dry your graduated cylinder with a paper towel. 9. Use your clean dry 100 mL graduated cylinder to measure 15 mL of the iron acetate solution from the Erlenmeyer flask. 10. Place the thermometer into the beaker and record the initial temperature (Time = 0) in Table 3. As with all experiments in this Lab course, record all temperatures to one decimal place, i.e. ±0.1oC. . Hint: Before proceeding to the next step, get your clock/stopwatch ready, have your Table 3 in front of you and a reliable pen or pencil. 11. Add the 15 mL of the iron(II) acetate solution into the 500 mL beaker. 12. Use Table 3 to record the temperature and color of the solution every ten seconds for two minutes. 13. When the reaction is complete take a picture of your set up.

Table 3: Temperature and Color Change Data Record all temperatures to one decimal place, i.e. ±0.1oC. Time (seconds) Temperature (degrees C) Color 0 27.0 Whitish yellow 10 28.0 Pale yellow 20 28.0 Pale yellow 30 28.0 Pale yellow 60 29.0 Dim yellow 90 29.0 Bright yellow 120 29.0 Bright yellow The instructions ask you to record color and temperature every 10 minutes, from 0 seconds through 2 hours. This is a bit much, so just make your measurements and observations every 10 minutes for the first 30 minutes, then every half-hour until a total fo 2 hours.

Post-Lab Questions:

1. The oxidation-reduction reaction that was performed in Part 1 is: Fe(s)+ 2 HC2H3O2(aq) ? Fe(C2H3O2)2(aq) + H2(g)

a. What substance was reduced in this reaction? Note that only reactants (not products) are reduced.

b. What substance was oxidized in this reaction? Note that only reactants (not products) are oxidized.

2. The oxidation-reduction reaction that was performed in Part 2 is: 2 Fe(C2H3O2)2(aq) + H2O2(aq)+ 2H+(aq) + 2 C2H3O2-(aq) ? 2 Fe(C2H3O2)3(aq) + 2 H2O(l)

a. What substance was reduced in this reaction? Note that only reactants (not products) are reduced.

b. What substance was oxidized in this reaction? Note that only reactants (not products) are oxidized.

3. What color change did you observe? Why does the oxidation change result in a color change? Hint: re-read the Introduction in the lab Moodle shell.

4. Consider the equation in question 2. When the acetate anion is removed from the equation and the results simplified, the Net Ionic Equation below is obtained for the Oxidation-Reduction: 2 Fe2+ + H2O2 + 2H+ ? 2 Fe3+ + 2 H2O Split the above Oxidation-Reduction reaction into half-reactions, the Oxidation and the Reduction halves. Complete each by writing in the proper number of electrons and correctly balancing each half-reaction. Use the Introduction in the lab Moodle shell as a guide. Oxidation: Reduction:

5. Does the temperature of the reaction increase or decrease as the reaction proceeds? Explain why this happens.

Explanation / Answer

1) The reaction taking place in the first part of the lab is

Fe (s) + 2 HC2H3O2 (aq) --------> Fe(C2H3O2)2 (aq) + H2 (g)

a) Acetic acid ionizes in aqueous solutions to proton (H+) and acetate ion.

HC2H3O2 (aq) --------> H+ (aq) + C2H3O2- (aq)

The protons gain electrons to form molecular hydrogen.

2 H+ (aq) + 2 e- --------> H2 (g)

Reduction is defined as the addition of one or more electron(s) to an ion or molecule. The proton accepts an electron; hence, the proton is reduced. The ionization of acetic acid furnishes the proton and hence, acetic acid is reduced in this reaction.

b) The oxidation state of elemental iron (Fe) is 0 while the oxidation state of iron in iron (II) acetate is +2. Oxidation is defined as the removal of one or more electron(s) from an ion or molecule. Since Fe loses electrons, hence, iron is oxidized in this reaction.

2) The reaction taking place in the second part of the lab is

2 Fe(C2H3O2)2 (aq) + H2O2 (aq) + 2 H+ (aq) + 2 C2H3O2- (aq) --------> 2 Fe(C2H3O2)3 (aq) + 2 H2O (l)

a) The oxidation states of oxygen in H2O2 and H2O are -1 and -2 respectively. Since the oxidation state of oxygen decreases in the reaction, hence, H2O2 is reduced in the reaction.

b) The oxidation state of iron in Fe(C2H3O2)2 is +2 while the oxidation state or iron in Fe(C2H3O2)3 is +3. Since the oxidation state of iron increases, hence, Fe(C2H3O2)2is oxidized in the reaction.

3) Iron (II) salts are pale in color while iron (III) salts are intense yellow or orange in color. Hence, the oxidation reaction in the second part of the lab results in a color change of the solution from pale (almost colorless) to intense brownish-red or orange. The yellow or orange color of iron (III) salts is due to transitions of d electrons between available energy shells, i.e, d-d electronic transitions.

4) The net ionic equation for the oxidation reaction in the second part of the lab is

2 Fe2+ (aq) + H2O2 (aq) + 2 H+ (aq) ---------> 2 Fe3+ (aq) + 2 H2O (l)

Oxidation is defined as the removal of electrons from an ion or molecule while reduction is the addition of electrons. Clearly, we can see that Fe3+ is formed from Fe2+ by losing an electron. Therefore, this is the oxidation reaction. The half reactions are given below.

Oxidation: Fe2+ (aq) ---------> Fe3+ (aq) + e-

Reduction: H2O2 (aq) + 2 H+ (aq) + 2 e- --------> 2H2O (l)

5) The oxidation of iron (II) acetate yields iron (III) acetate. Iron (III) is more stable due to half filled configuration of the 3d orbitals and hence, less reactive. Consequently, iron (II) salts are less stable and more reactive. Thus, in this reaction, a less stable iron (II) salt is oxidized to a more stable iron (III) salt. Thus, the reaction must release energy and hence, the temperature of the reaction is expected to rise during the reaction.

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