An Observation of a Single Replacement Reaction with Iron and Copper

Single Replacement Lab

Purpose: The purpose of this lab was to observe a single replacement reaction with iron and copper. Through the observations, the students were able to see the activity series and the changing of electrons and examine an oxidation/reduction reaction. In addition, the students were able to confirm the values of the coefficients for the balanced chemical equation between the iron nails and the copper chloride dihydrate solution.

Hypothesis: If the two iron nails are placed within the copper chloride dihydrate solution, then the amount of moles of solid iron lost during the reaction will have a one-to-one ratio with the amount of solid copper because both substances have a coefficient of one in the balanced chemical equation.

Theory: The activity series is a series of elements arranged in descending order of chemical activity. Iron is higher than copper on the activity series, thus creating the chemical reaction observed in the lab. In the aqueous state, both elements have a 2+ bond with the chloride. Reduction refers to a chemical reaction in which electrons are gained and oxidation refers to a chemical in which electrons are lost. In this lab, the iron is oxidized and the copper is reduced to a solid. One mole of copper chloride equates to 134.452 grams and one mole of iron chloride equates to 126.753 grams. The accepted balanced equation for this reaction is:

CuCl2 (aq) + Fe(s) à FeCl2 (aq) + Cu(s) .

Variables:

Independent Variable: Number of iron nails

Dependent Variable: Moles of copper

Controlled Variables: Time, temperature of solution, air temperature, crucible tongs, amount of copper chloride dihydrate, same balance, types of beakers

Materials:

1. Safety Goggles
2. Gloves
3. Digital Balance to the 100th place in grams
4. Paper towels
5. 2 250 ml Beakers
6. Unspecific amount of copper chloride dihydrate
7. 2 Iron Nails
8. Steel Wool
9. Distilled Water
10. Wash Bottle
11. Crucible Tongs
12. Hot Plate
13. Timer

Procedure:

1. Measured mass of beaker
2. Cleaned iron nails with steel wool
3. Measured mass of iron nails
4. Added 50 mL of copper(II) chloride solution to beaker
5. Carefully slid both nails into copper chloride solution
6. Let beaker sit for 30 minutes and observe
7. Removed one nail with crucible tongs
8. Rinsed adherent reaction product off nail into reaction beaker using distilled water from wash bottle
9. Repeated step 8 with second nail
10. Put nails on paper towel and let them dry
11. Decanted liquid portion of reaction solution into another 250 mL beaker
12. Poured decanted solution into the sink
13. Used 25 mL of distilled water and washed reaction product in beaker
14. Decanted wash water into 250 mL collection beaker
15. Repeated steps 13-14 two more times
16. Poured content of collection beaker into sink
17. Let reaction beaker with solid product dry for 48 hours
18. Measured mass of dry nails
19. Measured mass of beaker and dry reaction product
20. Disposed of nails and solid product in waste container
21. Recorded all results in data table

Qualitative Observations:

1. Head of iron nails turned eraser-like red
2. Copper chloride solution gradually became darker, light blue to dark blue
3. Red copper easily removed from nails
4. Thin layer of red copper on second nail
5. Solid copper in beaker is powdery and red
6. Decanting created a murky brown collection container

Results:

Sample calculations:

Mass of iron nails (before reaction) = (Mass of beaker + mass of iron nails) – (mass of beaker)

2 Iron Nails: (81.78 grams) – (77.72 grams) = 4.06 grams of iron

Mass of copper = (Mass of beaker + copper) – (mass of beaker)

Dry Product: (78.64 grams) – (77.72 grams) = 0.92 grams of copper

Mass of iron lost by nails = (Mass iron nails before reaction) – (mass iron nails after reaction)

Iron Lost: (4.06 grams) – (3.26 grams) = 0.80 grams of iron

Moles of iron = (mass of iron in grams) X (1 mole of iron/55.85 grams of iron)

Moles of iron: (0.80 grams) X (1 mole of iron/55.85 grams of iron) = 0.014 moles of iron

Moles of copper = (mass of copper in grams) X (1 mole of iron/63.55 grams of copper)

Moles of copper: (0.92 grams) X (1 mole of iron/63.55 grams of copper) = 0.014 moles of copper

Mole ratio of iron to copper = (moles of iron) : (moles of copper)

Mole Ratio: (0.014 moles of iron) : (0.014 moles of copper) =

1 mole of iron : 1 mole of copper

Item Mass in Grams

Empty dry beaker 77.72 grams

Nails (before reaction) and beaker 81.78 grams

Iron nails (before reaction) 4.06 grams

Iron nails (after reaction) 3.26 grams

Dry product and beaker 78.64 grams

Table 1: Mass Observations

Iron Lost by Nails Dry Copper Product

Mass in grams 0.80 grams 0.92 grams

Moles 0.014 moles of Fe 0.014 moles of Cu

Accepted Value 1 mole of Fe to 1 mole of Cu

Experimental Value 1 mole of Fe to 1.01 moles of Cu

Percentage Error 1.1%

Table 2: Iron and Copper Comparisons and Error

Table 3: Iron and Copper Comparison Chart

Conclusion:

Although the amount of grams was different, the comparison of the number of moles of both copper and iron was consistent with the accepted value. The hypothesis was supported by the results of the experiment because a one-to-one ratio was created and observed. Since iron was more active on the activity series, the iron molecules chemically bonded with the chloride in the place of the copper ions. Through the process of reduction, these copper molecules gained the electrons and became a solid. The reddish substances observed are the copper molecules on the two iron nails. Furthermore, the copper on the nails was easily removed because the copper did not bond with the iron nails. During the decanting process, the copper stayed red since it had already changed into a solid. Even though only one trial was performed, the experimental value was extremely accurate, with a margin of error of only 1.1%. The mass of iron lost and the mass of the dry copper product directly correlated in the calculation of the mole ratio. However, there was one main sources of error during the experiment. The second nail was dropped into the beaker with the copper chloride solution during the rinsing process and attracted an extremely thin layer of copper that could have affected the results.

Evaluation of Procedure:

The main weakness of the procedure was the unspecified time frame. Although the experiment needed the solid product to be dry to cut out any source of error, the procedure did not specify how long the nails should dry for. If more trials were carried out to test the precision of the results, a specific time frame would be needed in order to eliminate experimental error. The procedure also asked to measure the mass of the substances to the hundredths place and not the thousandths place. The changes in the thousandths place could have changed the percentage error and the results since less than a gram of each substance was tested in the experiment. The 250 mL beaker also did not fit both nails without laying one nail on top of the other.

Improving the Investigation:

The addition of a balance to the thousandths place instead of the hundredths would give a better observation of the measured substances. In addition, only one trial took place for the experiment. In order to improve the investigation, more trials are needed to calculate the precision of the trials to the accepted value. The nails had to lay on top of each other in order to maximum the space in the 250 mL beaker. A bigger or secondary beaker would eliminate the contact between the two nails and shift the results of the lab.

Additional Questions:

Copper could be lost in this experiment during the washing and decanting steps. How would this effect the iron: copper mole ratio? Explain.

Since less copper was used in the equation as a result of decanting, the molar mass of the copper was slightly smaller than the amount of copper on the nails. In the results, the moles of copper were slightly bigger than the moles of iron. If less copper was lost, the margin between the moles of copper and the moles of iron would widen.

What other factors might account for any error in your mole ratio?

Since the second nail fell into the beaker, it attracted a small layer of copper. During the washing and decanting process, a small amount of copper was lost and some of the red substance stayed in the original beaker. A layer of copper formed on the tongs during the washing process.

Examine the data collected by other members of the class. Were the masses of iron and copper the same in all experiments? Were the mole ratios the same? Does the mole ratio of a substance in a chemical equation depend on the amounts of reactants used?

The mass ratios were different for all the students even though the mole ratios were the same. All other students also had a one-to-one ratio between the moles of copper and moles of iron. The mole ratio did not depend on the amounts of reactants used during the lab.