Types of Chemical Reactions

CHEMISTRY

UNIT: CHEMICAL REACTIONS

TYPES OF CHEMICAL REACTIONS

How can you determine the products of a chemical reaction? By just examining the formulas for the reactants, many different products could be predicted. To find clues, chemists look for observable physical changes such as gas production, radiation of heat, formation of a precipitate, or color changes. They also know that many reactions can be classified as synthesis (combination), decomposition, single replacement, or double replacement.

In this lab you will observe what happens when a number of different substances are heated or combined with other substances. Your task is to verify the identity of at least one of the products, determine the type of reaction, and write a balanced chemical equation to summarize your findings.

OBJECTIVE

When you have completed this activity, you should be able to:

Identify and classify chemical reactions based on five general categories.

MATERIALS

PROCEDURE

1.  Put on your goggles and lab apron.

2.  As you perform each investigation record all observations in the DATA TABLE. Include appearance of reactants and products, evidence that a reaction is taking place, results of tests for gases, and any other relevant data.

3.  Using crucible tongs, hold a 2 cm strip of Mg ribbon in the hottest part of the burner flame. Place the reacted ribbon on a clean watch glass. Record your observations and describe the resulting product.

CAUTION: Do not look directly at burning magnesium.

4.  Place a test tube in the test-tube rack. Have a second test tube ready in a test-tube holder. Add 5-10 mL of 3.0M HCl to the first test tube. Drop a 2-cm piece of Mg ribbon into the acid.

CAUTION: Hydrochloric acid is corrosive. Avoid spills and splashes.

Hold the second test tube over the mouth of the first test tube, as shown in the figure below. When the reaction appears to have ended, light a wood splint and quickly test the collected gas by holding the burning splint near the mouth of the second test tube.

CAUTION: You may hear a loud popping noise.

5.  Place approximately 5 mL of hydrogen peroxide, H2O2, into a test tube. Have a wooden splint and matches ready. Add a very small amount (about the tip of the scoopula) of manganese (IV) dioxide, MnO2, to the hydrogen peroxide. As the reaction occurs, light the splint and allow it to burn freely for 5 seconds. Blow the flame out and place the glowing splint halfway into the test tube.

6.  Carefully place about one scoopula of ammonium carbonate, (NH4)2CO3, into a test tube. Holding the test tube with a test-tube holder, heat the solid gently by holding the test tube in the flame for a few seconds, then removing it for a few seconds. Continue heating in this manner for 1 minute. As you heat the solid gently waft toward your nose to detect any odor.

CAUTION: When heating the test tube, point the open end away from yourself and anyone else. The gas coming from the tube is an irritant so avoid inhaling deeply.

Continue to heat the solid and place a burning splint at the mouth of the test tube.

Continue to heat the solid and place a piece of blue cobalt chloride test paper just inside the mouth of the test tube.

7.  Place a drop of potassium iodide solution, KI, on a glass plate. Add a drop of lead (II) nitrate solution, Pb(NO3) 2.

8. Place a piece of aluminum foil in a test tube and add approximately 3 mL of 1.0 M CuSO4. Observe until changes are observed with the aluminum and the solution.

Note any temperature change.

9.  Place about 1 mL of 1.0 M NaOH in a test tube. Add one drop of phenolphthalein indicator. Add dropwise, while stirring, enough 3.0 M HCl just to produce a color change.

CAUTION: Avoid skin or clothing contact with NaOH and HCl.

Holding the test tube with the test-tube holder, heat the contents gently over a flame until dry. Let cool in test-tube rack.

10.  Combine small amounts of iron filings, Fe, and powdered sulfur, S, in a test tube. Test for magnetism by moving a bar magnet along the side of the test tube. Using a test-tube holder, heat the mixture gently, then vigorously, for several minutes over a flame. Place the tube in the test tube rack and test again with the magnet

CAUTION: This heating must be done in a fume hood.

11.  Place a small amount (the tip of a scoopula) of copper (II) carbonate, CuCO3, in a test tube. Insert the gas delivery tube into the rubber stopper.

CAUTION: Glass tubing breaks easily. Handle with care.

Place the stopper assembly into the test tube. Prepare another test tube with about 5 mL of limewater. Light the Bunsen burner. Holding the tube containing the copper carbonate with the test-tube holder, heat the solid. As the copper carbonate is heated, push the end of the gas delivery tube into the limewater.

limewater

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