Writing an Balancing Chemical Equations by cuiliqing


									Writing and Balancing Chemical Equations                NAME:______________________
Honors Chemistry                                        November 10, 2004 F106

Introduction: Chemists observe what is happening in a chemical equation and try to describe it
in language that is simple and clear. A chemical equation uses formulas and symbols to describe
substances involved in a reaction, the physical state of the substance, the use of a catalyst, and the
relative proportions. The general form of an equation is:
                          Reactants → Products
In this investigation you will perform a series of reactions and make careful observations of the
changes that occur. You will write chemical equations to describe the reactions.

Safety: Wear goggles at all times. Avoid looking at the magnesium as it burns. Tie back loose
hair and clothing when working with a flame. Hydrochloric acid is corrosive. Ammonia is a skin
and respiratory irritant, so avoid inhaling it deeply. Clean spills immediately. Note all safety

1. Obtain a piece of Mg ribbon. Light the bunsen burner flame. Hold the Mg ribbon with your
    tongs over a watch glass and ignite in flame.
2. Place 10 ml of 6M HCl into a test tube and test tube rack. Put a piece of Mg ribbon into test
    tube and cover it with a second inverted test tube. When the reaction appears to have ended,
    light a wooden splint and quickly test the collected gas for flammability by inserting the lit
    splint into the mouth of the inverted test tube. Note:The H2 gas will make a popping sound.
    The other product is aqueous magnesium chloride.
3. Light the burner flame and grasp a small piece of Cu foil with your tongs. Heat in the flame
    until it is red hot. Remove it from the flame and allow to cool. Scratch the surface with a
    sharp object. A single solid product is made.
4. Place a small scoop of ammonium carbonate((NH4)2CO3) into a test tube. Gently heat by
    holding the test tube in the flame for a few seconds, then removing it for a few seconds.
    Continue for 1 minute and carefully waft the ammonia fumes towards your nose. Continue to
    heat the solid, place a burning splint at the mouth of the test tube. Finally, place a piece of
    blue cobalt paper just inside the mouth of the test tube.
5. Place approximately 10-15 ml of hydrogen peroxide(H2O2) into a test tube. Have a wooden
    splint ready. Add a small amount of manganese (IV) oxide, MnO2. Light the splint for 5
    seconds and then blow it out, place the glowing splint halfway into the test tube. The gas
    released is oxygen.
6. Place a drop of potassium iodide(KI) into a well plate. Add a drop of lead (II) nitrate
7. Add 5 ml of 1M sodium sulfite(Na2SO3) into a test tube. Add 1 ml of 6M HCl. Note the odor.
    Do NOT smell the gas directly. The gas is sulfur dioxide. The other products are sodium
    chloride and water.
8. Use forceps to hold a few strands of steel wool in the hottest part of the flame. The product is
    iron (III) oxide.
9. Add 10 ml of 6M HCl and 10 ml of 6M NaOH. Test reactants and product with pH paper.
10. Observe a candle burning. The wax has a formula of C25H52 and the products are carbon
    dioxide and water.
11. Observe the electrolytic decomposition of water into two gases.

Obervation and Data:
Procedure                Before Reaction               After Reaction           Reaction Evidence
1. Write a word equation for the reactions in each of the procedures.
2. Write a balanced chemical equation for each procedure.
3. What is the test for hydrogen gas?
4. What is the test for oxygen gas?
5. What is the test that indicates whether a solution is acidic or basic?
6. What is the test for carbon dioxide gas?
7. Write balanced equations for #3,4, and 6.
8. For each of the following situations, determine the identity of the gas produced. Write a
   balanced chemical equation for each reaction.
       a. When potassium bromate(KBrO3) is heated, it decomposes into potassium
       bromide(KBr) and a gas that supports the combustion of a glowing splint.

        b. Sodium metal reacts violently with water to produce soidium hydroxide(NaOH) and a
        gas that ‘pops’ in the presence of a burning splint.

        c. The recipe for the volcanic eruption used in many science projects is the reaction of
        baking soda(NaHCO3) and vinegar/acetic acid(HC2H3O2). When these compounds are
        mixed together, the salt sodium acetate(NaC2H3O2) is formed as well as a gas that
        extinguishes a burning flame and a substance that turns blue cobalt chloride paper pink.

9. What are the steps to lighting a bunsen burner?

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