To Write Formulas of Reactants and Products Involved in a Chemical Reaction

Naming compounds and writing formulas for a series of copper reactions / ‘Cu’ Later

INTRODUCTION:

Substances may be created by chemical change and may also undergo chemical change. If a substance is produced as a result of a chemical change or reaction, it is called a product. If a substance is the subject of a chemical change, it is called a reactant. The same substance can be either a reactant or a product, depending on the chemical reaction.

One way of knowing that a chemical change has occurred is by observing that the properties of the products are different from those of the reactants. The new products can then become the reactants in another chemical reaction. In this experiment, a solution of copper(II) nitrate (cupric nitrate) is treated with a series of different reactants and the sequence of changes that occurs is observed. All of the reactions take place in the same test tube. Look for evidence that a new substance has formed from each chemical change.

The chemical conversion of one product into another useful product is called recycling. The copper(II) nitrate solution used in this experiment is prepared originally from elemental copper and nitric acid. After a series of chemical reactions, the copper metal is recovered.

Chemical changes are required to make these conversions. For example, the metals that are changed into alloys and shaped into soft drink cans are themselves converted by chemical changes into other products. Recycling enables people to reuse scarce natural resources, such as copper and aluminum, usually at a lower cost than mining ores and refining them.

OBJECTIVES:

·  To write formulas of reactants and products involved in a chemical reaction.

·  To observe the types of evidence that indicate a chemical change has taken place.

·  To infer from the observation of chemical change that a new substance has formed.

MATERIALS:

copper(II) nitrate solution hydrochloric acid

sodium hydroxide solution aluminum wire

small Pyrex test tube stirring rod

100-mL beaker iron ring

ring stand ruler

wire gauze lab marker

Bunsen burner test tube rack

PROCEDURE:

PART I

1.  In a 100-mL beaker, make a hot water bath by heating until boiling 50-mL of tap water.

2.  While the water bath is heating, make three marks that are 1 cm apart on a small test tube. Make the marks from the bottom up.

3.  Add copper(II) nitrate solution up to the first mark on the test tube.

4.  Add sodium hydroxide solution to the second mark on the test tube. Mix with the stirring rod and then rinse of the stirring rod.

5.  Touch the bottom of the test tube to determine whether any heat has been released or absorbed. Record the observation in the Observations Table.

6.  The copper(II) nitrate has been converted to copper(II) hydroxide. The other product is sodium nitrate.

PART II

1.  Place the test tube in the hot water bath begun in Part I.

2.  Heat the test tube until no more change occurs. Observe and record in the Observations Table.

3.  The products of this reaction are copper(II) oxide and water.

PART III

1.  Turn off the burner and then remove the test tube from the hot water bath.

2.  Cool the test tube and its contents for two minutes in room temperature water.

3.  Add hydrochloric acid to the third mark; mix with the stirring rod and then rinse the rod.

4.  Observe any changes and record in the Observations Table.

5.  The products of this chemical reaction are copper(II) chloride and water.

PART IV

1.  Place a 12-cm piece of aluminum wire in the test tube. Leave it until no more reaction is observed taking place.

2.  Touch the bottom of the test tube to check for any temperature change.

3.  Record all observations in the Observations Table.

4.  The copper compound has finally been converted back into copper metal. The other product is aluminum chloride.

CONCLUSIONS:

Answer these questions on a separate piece of paper.

1.  List three observations that indicate a chemical change may have occurred. Be specific.

2.  In the last step of this experiment, where is the aluminum chloride? How could it be recovered?

3.  What is the color of solutions of copper(II) compounds?

4.  What is the color of copper(II) oxide?

5.  Are parts I and IV exothermic or endothermic? Explain.

6.  Write a word equation for each of the four chemical changes. Refer to the procedure to determine what the reactants and products are in each reaction.

7.  Write the formula equation under each word equation.

Observations Table

Observations
Part I
Part II
Part III
Part IV