Chemistry I

Discovery 5-2Name

Types of Chemical ReactionsPeriod___

There are five basic types of reactions that occur. The first four will be covered in this discovery. The state symbols are indicated after each formula: (s) means solid; (l) means liquid; (g) means gas; (aq) means aqueous solution (i.e. solid dissolved in water).

1) Synthesis (Combination)—two or more substances combine to form a single substance.

Example: S(s) + O2(g)  SO2(g)

2) Decomposition—a single compound is broken down into two or more products.

Example: CaCO3(s)  CaO(s) + CO2(g)

3) Single-Replacement—atoms of one element replace the atoms of a second element in a compound

Example: Mg(s) + 2AgNO3  Mg(NO3)2(aq) + 2Ag(s)

4) Double-Replacement—involves an exchange of positive ions between two reacting compounds.

Example: FeS(s) + 2HCl(aq)  H2S(g) + FeCl2(aq)

5) Combustion—a carbon compound is burned in oxygen to form carbon dioxide and water.

Example: C6H12O6 (s) + 6 O2 (g)  6 CO2 (g) + 6 H2O (l)

This discovery can be completed in any order. Follow ALL directions carefully. Wear goggles. Wash your hands after completing this discovery.

Part A: Synthesis (Combination) Reaction [Teacher Demo]

  1. Determine the mass of a watch glass together with a piece of compacted steel wool.
  2. Hold your tongs in the hot part of the burner flame for about 1 minute to remove any contamination.
  3. With the tongs, hold the steel wool in the hot part of the flame for 5 minutes. Observe what is happening during and after heating.
  4. Allow the steel wool to cool one minute before returning it to the watch glass.
  5. Determine the mass of the watch glass and the product.
  6. Dispose of the solid in the trash can.
  7. What evidence do you have that a chemical reaction took place?
  1. What caused the mass to go up? What did the iron in the steel wool combine with?
  1. Using the reaction in the introduction as your guide, write a chemical equation to explain what happened in this reaction. Assume the iron in the steel wool has an ionic charge of +2.
  1. Explain why this reaction is classified as a synthesis (combination) reaction.

Part B: Decomposition Reaction

  1. Add one small scoop of copper (II) sulfate pentahydrate, CuSO45H2O(s), to a clean dry test tube. The “pentahydrate” means that the compound has five water molecules within the copper (II) sulfate crystals. Observe and record the appearance of the solid.
  1. Determine the mass of the test tube and sample.
  2. Using a test tube holder, tilt the test tube horizontally, spreading the solid so it forms a single layer on the side of the test tube. Move the test tube back and forth through a cool flame (no inner blue cone) so that the entire sample is heated. Heating will be completed in about 2 minutes (you have heated too much if the solid begins to darken). Observe what is happening to the crystals and inside the test tube during and after heating.
  3. Allow the test tube and contents to cool. Determine the mass.
  4. Use an eye dropper to add a couple of drops of water to the substance in the test tube.
  5. Dispose of the chemical in the product jar labeled CuSO4 in the fume hood.
  6. What evidence do you have that a chemical reaction took place during heating?
  1. Did the mass go up or down? If it went up, what did it combine with? If it went down, where did it go? (Hint: look at the formula of the original sample)
  1. Using the reaction in the introduction as your guide, write a chemical equation to explain what happened in this reaction.
  1. Explain why this reaction is classified as a decomposition reaction.

Part C: Single-Replacement Reaction

  1. (a) Place 15 drops of copper (II) sulfate solution, CuSO4(aq), in a well of a microplate. Add a small piece of magnesium, Mg(s). Observe what happens over the next 5 minutes.
  2. (b) Place 15 drops of hydrochloric acid solution, HCl(aq), in another well. Add a small piece of zinc, Zn(s). Observe what happens over the next 5 minutes.
  3. When the reactions are complete, rinse the products down the sink. Rinse and dry the remaining zinc and return it to the container. Any other solid waste can go in the trash can.
  4. What evidence do you have that a chemical reaction took place?

a.

b.

  1. Using the reaction in the introduction as your guide, write a chemical equation to explain what happened in this reaction.

a.

b.

  1. Explain why these reactions are classified as single-replacement reactions.

Part D: Double-Replacement Reaction

  1. (a) Place 3 drops of barium chloride solution in a well of a microplate. Add 3 drops of potassium sulfate solution. Observe what happens.
  2. (b) Place 3 drops of cobalt (II) nitrate solution in another well. Add 3 drops of ammonium carbonate, (NH4)2CO3. Observe what happens.
  3. Rinse the products down the sink with plenty of water. What evidence do you have that a chemical reaction took place?

a.

b.

  1. Using the reaction in the introduction as your guide, write a chemical equation to explain what happened in this reaction.

a.

b.

  1. Explain why these reactions are classified as double-replacement reactions.