Experiment : Types of Chemical Reactions
Introduction
We can categorize chemical reactions according to the way in which the atoms or molecules of the reactants form new groupings. Many chemical reactions can be classified as belonging to one of four main groups.
Syntheses 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.
Decompositions 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 from,
AB -- A + B
Singledisplacements are reactions in which an element reacts with a compound and replaces one of the elements in the compound. These reaction are represented by the general equation,
A + BC -- AC + B
Double displacements are reactions in which atoms or groups of atoms are exchanged between two reactants, forming two new products. Precipitation and neutralization are two major types ofdouble displacement reactions. These reactions are of the general type,
AB + CF -- AD + CB
In this experiment you will observe nine different chemical reactions and identify the type of each reaction on the basis of the products formed.
PROBLEM How are chemical reactions categorized on the basis of experimental evidence?
Apparatus: 6 test tubes Pipettes
Crucible tongs utility clamp
10 mL graduated cylinder
Materials Wooden splints 6% hydrogen peroxide (H2O2)
Manganese dioxide (MnO2) 0.10 M silver nitrate (AgNO3)
Copper (Cu) 0.50 M barium hydroxide (Ba(OH)2)
Phenolphthalein sodium hydrogen carbonate (NaHCO3)
pH paper
0.50 M ammonium hydroxide (NH4OH) 0.50 M copper(II) nitrate Cu(NO3)2
Safety
Wear safety goggles and Lab aprons.
In your lab book
Observation section
1. Write out the chemicals as reactants for each reaction. ( 2 points)
2. Write a short observation of chemicals before placing them together. ( 2 points)
3. Write an observation of the chemicals when they are mixed. ( 2 points)
4. Write an observation of the products of the reaction. ( 2 points)
Analysis section
5. Answer the questions related to the reactions. (5 points)
6. Show complete balanced reaction. ( 4 points)
7. Categorize each of the reactions as a synthesis, decomposition, single displacement, or double displacement. (2 points)
Example
Title: Hydrogen Peroxide + Manganese Dioxide à
Pre Observation:
Reaction Observation:
Post Observation:
Analysis:
Question
Full reaction with Reactants and products
Reactant à Products
Procedure:
Experiment 1
Place approximately 5 mL of hydrogen peroxide in a 50 mL beaker, add a pinch of manganese dioxide, and observe.
Make visual and auditory observations for chemical reaction.
Experiment 2
Place a piece of copper metal into a 50 mL beaker. Place 3 2 -3 drops of silver nitrate onto the copper metal. Observe. Be patient; it may take a few minutes for the reaction to occur.
CAUTION: be careful not to get silver nitrate on your skin?
Experiment 3
Place approximately 3 mL of barium hydroxide solution in a test tube and add on drop of phenolphthalein. Using a pipette add sulfuric acid one drop at a time until the color just disappears. Note the appearance of the contents of the test tube.
Experiment 4 DO NOT DO!
Place approximately 2 g of sodium hydrogen carbonate in a test tube, fit the test tube with a one-hole stopper and delivery tube, and clamp it. 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 hydrogen carbonate and observe the limewater. Remove the delivery tube from the limewater before you discontinue heating. Test the condensate that collects near the top of the test tube with litmus paper. Compare the residue left in the test tube after heating with some of the original sodium hydrogen carbonate.
Experiment 5 DO NOT DO!
Polish a piece of copper foil with steel wool until is clean and shiny. Vigorously rub the copper with a lump of sulfur until the foil changes in appearance.
Experiment 6
Pour about 3 mL of ammonium hydroxide solution and 3 mL of copper (II) nitrate solution in a test tube. Use pipettes to transfer solutions; about three pipettes of each.
Questions
Experiment 1:
1. How do you know a reaction occurred? List two ways.
2. What substance was being produced?
3. Water is another product of this reaction. Where is it?
Experiment 2:
1. What substance formed on the surface of the copper when it was placed in a silver nitrate solution?
2. Where did this substance come from?
3. What change is there in the appearance in the test tube?
4. What is the other product?
Experiment 3:
1. Why does the phenolphthalein turn pink in barium hydroxide?
2. Why does it eventually turn colorless when sulfuric acid is added?
3. What is the chemical name of the precipitate formed in the test tube?
4. What is the other product?
Experiment 4:
1. What change did you observe in the appearance of the limewater?
2. What did the pH paper tell us about the different areas of the reaction?
3. What is a product of the reaction?
4. Is there any change in the appearance of the solid in the test tube?
Experiment 5:
1. What is the substance formed when the sulfur is rubbed on the copper foil?
Experiment 6:
1. When copper (II) nitrate 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.
2. What is the chemical name of the product formed?