Background

By now you are familiar with seeing and working with balanced chemical equations. But how do you know the coefficients in these equations are correct? Do the coefficients reflect how the chemical substances actually combine? In this experiment, you will determine the values for the coefficients used in a balanced chemical equation. the coefficients you are trying to determine are for the reaction of iron metal with a copper(II) chloride solution, which produces copper metal and an iron compound.

You will use the fact that the coefficients of the substances in a chemical equation represent the relative number of moles of each substance involved in the reaction. You will determine the relative numbers of moles of each reactant and product in the reaction you observe. From the mole ratios, you will derive the appropriate coefficients to be used in the chemical equation. If your experiment is successful you should be able to determine the mole ratio of the iron used to the copper produced.

Goals

·Measure the number of moles of iron consumed and copper produced in the reaction of iron with aqueous copper(II) chloride.

·Write a balanced chemical equation for the reaction.

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Equipment
 

safety goggles	2 drying oven/class or
1 50-mL graduated cylinder	2 heat lamps/class
2 250-mL beakers	1 crucible tongs
1 plastic wash bottle	8 centigrams balances/class
1 glass stirring rod	1 glass-marking pencil/class

Materials
 

iron nails, Fe	steel wool
1 M copper(II) chloride dihydrate, CuCl2 . 2H2O	paper towel
	distilled water

Safety

Copy Tables 12.1 and 12.2 into your laboratory notebook. As you perform the experiment, record your data in Table 12.1 and your observations in Table 12.2.

Day 1

1. Using a glass-marking pencil, label a clean, dry 250-mL beaker with your name.

2. Add 50 mL of copper(II) chloride solution to the beaker.
3. Clean two iron nails with steel wool to remove any rust or protective coatings. Determine the combined mass of the nails to the nearest 0.01 g and record.
4. Slide the nails carefully into the solution of copper (II) chloride. Let the beaker stand undisturbed for at least 20 minutes. Record any evidence of a chemical reaction in Table 12.2.
5. Using crucible tongs, remove one of the nails from the reaction solution. Hold the nail over the reaction beaker. Rinse th adherent reaction product off the nail and into the beaker, using a jet of distilled water from a wash bottle, as shown in Figure 12.1. Repeat this procedure for the second nail.
6. Allow the nails to dry on a paper towel in a safe place. (You will remeasure their mass later.)
7. Carefully decant the liquid portion of the reaction solution into another 250-mL beaker, as shown in Figure 12.2. Leave the solid reaction product in the original beaker. Dispose of the decanted solution by pouring it into the sink.
8. Use 25mL of distilled water to wash the reaction product contained in the beaker. Decant the wash water into the collection container. Repeat the washing and decanting procedures two more times, being careful to avoid losing any reaction product. Pour the contents of the collection container into the sink.
9. Give the reaction beaker containing the solid product to your teacher to be dried.

10. Determine the combined mass of the dry nails to the nearest 0.01 g and record the measurement.
11. Determine the mass of the beaker and the dry reaction product to the nearest 0.01 g and record the measurement. When you are finished, dispose of the nails and the solid product in a waste conatiner.

Table 12.1 Mass Determinations

Item Weighed	Mass
Empty dry beaker
Iron nails (before reaction)
Iron nails (after reaction)
Beaker and dry product

Table 12.2 Observations

Step	Observations

Data Analysis

1. Determine the mass of iron lost by the nails.
2. Calculate the number of moles of iron used.
3. Determine the mass of the product produced.
4. Assuming that one of the products is copper metal, calculate the number of moles of copper produced.
5. Calculate the mole ratio of iron used to copper produced. Express this ratio as a simple whole- number ratio.

1. Calculate the percent error in your calue for the mole ratio. Your teacher will give you the accepted value.


Percent error= accepted value – experimental value  X 100 percent

accepted value
accepted value
2. Assuming that one product is iron (II) chloride, write a balance equation for the reaction. What type of reaction is this?
3. Copper could be lost in this experiment during the steps of washing and decanting. How would this effect the iron:copper mole ratio?
4. What other factors might account for any error in you mole ratio?
5. 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?

1. What test could you do to prove that the product is copper?
2. There was evidence that not all the copper chloride was consumed in this reaction. Describe the evidence. Design an experiment that would measure the amount of iron and copper chloride used. Show how you would calculate the mole ratio of copper chloride used to copper produced.
3. Identify two other cations besides the copper (II) ion tha would be used in this experiment. For one of your choices, design and carry out an experiment to find the mole ratio of iron used to metal produced.