SCH4C         Lab #5 - Types of Chemical Reactions

Introduction: We can categorize chemicals reactions according to the way in which atoms or molecules of the reactants form new groupings.  Many chemical reactions can be classified as belonging to one of four major categories.


Synthesis are reactions in which two or more substances combine to form a single new substance.  These reactions are generally of the form:
                                                A  +   B  ---->  AB

Very often the reactants are elements.


Decomposition's are reactions in which a single substance is broken down into two or more simpler substances.  The substances produced may be elements or simpler compounds.  Decomposition reactions are of the general form:

                                               AB   ---->   A  + B


Single Displacement  reactions are reaction in which an element reacts with a compound and replaces one of the elements in the compound.  These reactions are represented by the general equation:

                                              A  +  BC   ---->   AC  + B


Double Displacement reactions are reactions in which atoms or groups of atoms are exchanged between two reactants, forming two new products.  Precipitation, neutralization and combustion are three major varieties of double displacement reactions.  These reactions are of the general type:

                                              AB   +   CD   ---->   AD   +   BC


In this experiment you will observe nine different chemical reaction and identify the type of each reaction on the basis of the products formed.

Problem:   How can chemical reactions be categorized on the basis of experimental evidence?

Appartus: test tubes, Gas bottles, Crucible tongs, utility clamp, one-holed stopper, ceramic tile, pipettes, glass plates, retort stand, bunsen burner, gas delivery bottle, 10 mL graduated cylinder

Materials: wooden splints, 6% hydrogen peroxide, manganese dioxide, 0.1 M silver nitrate, copper wire, 0.5 M barium hydroxide, 0.5 M sulphuric acid, phenolphthalein indicator, carbon dioxide gas, magnesium ribbon, sodium hydrogen carbonate, fresh limewater, cobalt chloride paper, steel wool, sulphur rock, 0.5 M ammonium hydroxide, 0.5 M copper(II) nitrate,  chlorine gas

Procedure:
1.  Place 5 mL of hydrogen peroxide in a test tube, add a pinch of manganese dioxide, and observe.  (The manganese dioxide is a catalyst in this experiment).  Test the gas produced by inserting a glowing splint into the mouth of the test tube.
2.  Pour about 5 mL of silver nitrate solution into a test tube.  Place a small strip of copper foil in the silver nitrate solution and let the test tube stand for several minutes, and periodically observe both the strip and the solution.  CAUTION: Silver nitrate is an irritant, do not get it on your skin.
3. Place approximately 3 mL of barium hydroxide solution in a test tube and add one drop of phenolphthalein indicator solution.  Using a pipette, add sulphuric acid one drop at a time until the colour just disappears.  Note the appearance of the contents of the test tube.
4. Obtain a gas bottle filled with carbon dioxide gas.  ( Your teacher may indicate how you are to prepare your own sample of carbon dioxide).  Using crucible tongs, ignite a strip of magnesium ribbon, and quickly lower it into the gas bottle of carbon dioxide gas.  Observe the ash formed and the deposit on the sides of the gas bottle.
5. Place approximately 2 grams of sodium bicarbonate in a test tube, fit the test tube with a one-hole stopper and delivery tube, and clamp it to a retort stand.  Place 5 mL of limewater in a second test tube and place the end of the delivery tube in the limewater.  Gently heat the sodium bicarbonate and observe the limewater.  Remove the delivery tube from the limewater before you stop heating.  Test the condensate that collects near the top of the test tube with cobalt blue chloride test paper.  Compare the residue left in the test tube after heating with some of the original sodium bicarbonate. 
6. To the residue from the last test, after it is cool add some distilled water and a few drops of universal indicator.  Record your observations carefully.
7. To another test tube, add some sodium  bicarbonate, some distilled water and a few drops of universal indicator.  Again carefully record your observations.
8. Polish a piece of copper metal with steel wool until it is clean and shiny.  Vigorously rub the copper with a lump of sulphur until the foil changes appearance.  Describe the change. 
9. Pour approximately 3 mL of ammonium hydroxide solution and 3 mL of copper(II) nitrate solution in a test tube.  Describe the product that forms.
10. Your teacher will heat a piece of copper foil in a bunsen flame and then immediately plunge it into a bottle of chlorine gas.  Observe what happens.


 
Questions:
1. What happened when the glowing splint was inserted in the test tube containing hydrogen peroxide and manganese dioxide?  What substance was being produced?  Water is another product of this reaction.  Where is it?
2. What substance formed on the surface of the copper foil with it was placed in silver nitrate solution?  What did this substance come from?  What change is there in the appearance of the silver nitrate solution?  What other substance is produced in this reaction?
3. Why does the phenolphthalein turn pink in barium hydroxide?  Why does it eventually turn colorless when sulphuric acid is added?  What is the chemical name of the precipitate formed in the test tube?  What is the other product?
4. What are the specks that form on the gas bottle when magnesium is burned in carbon dioxide?  With what did the magnesium combine to form the ash?  Where did this substance come from?  What is the ash?
5. What change did you observe in the appearance of the limewater?  what is one of the products of the reaction?  Blue cobalt chloride paper turns pink on contact with water.  What is another product of the reaction?   Is there any change in the appearance of the solid in the test tube?  (The new substance in the test tube is sodium oxide.)
6. What is the approximate pH of the newly formed sodium oxide.  What is the approximate pH of the original sodium hydrogen carbonate?  Why do you think there was a change in the pH?
7. Describe the substance that is formed when copper foil is rubbed with sulphur.   What is the new substance?
8. When copper(II) nitrate solution is added to ammonium hydroxide solution, one of the products that forms is ammonium nitrate.  It is soluble and remains in solution.  Describe the appearance of the other product that forms.  What is its chemical name?
9. What substance was produced when heated copper foil was lowered into chlorine gas?  Describe its appearance.  Why was it necessary to heat the copper first?
10. Based on your answers to Questions 1 to 8, write a word equation for each reaction.   You may require some help for the next step, however, write a chemical equation for each of the word equations and balance them.  Categorize each reaction as a synthesis, decomposition, single displacement or double displacement reaction.