Lab 9: Topic III, Classifying Chemical Reactions

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Note:  After trying out the experiments for this lab, we decided to do some modifications. We will still do Home Scientist session III-3 today, but we will do Home Scientist sessions III-1 and III-2 on August 12 because they both work better with butane torch. Today we will do a precipitation/double-displacement reaction, as well as a gas-evolving reaction instead. We will also re-visit salting out from last week.

Reading:  The Home Scientist Lab Manual Topic III. Classifying Chemical Reactions. Introduction pp. 66-69. We will be doing Session III-3. Observe a single replacement reaction pp. 75- 76.

Experimental Title: Lab 9:  Classifying Chemical Reactions

Date of laboratory:  July 29, 2014

Purpose: The purpose of this lab is to explore various aspects of classifying chemical reactions. We will carry out a single replacement reaction, as well as a precipitation/double-displacement reaction and a gas-evolving reaction.

Introduction:

Read the introduction to this section in the lab manual, pp. 66-69, as well as the background to the experiment on page 75.

Chemical reactions may be classified in various ways.

One way to classify chemical reactions is by what type of chemistry is happening.

  • Precipitation reactions
  • Gas Evolution
  • Acid-base or Neutralization
  • Oxidation-Reduction 

 A second way to classify reactions is to look at what the atoms are doing.

  • Synthesis or combination
  • Decomposition
  • Displacement
  • Double-displacement

Equation for single-displacement reaction (part 1):

Fe (s) + CuSO4 (aq) –> FeSO4 (aq) + Cu (s)
Fe (s) + Cu2+ (aq) + SO42- (aq) –> Fe2+ (aq) + SO42- (aq) + Cu (s)

Equation for precipitation/double-displacement reaction (part 2):

MgSO4(aq) + Na2CO3(aq) → MgCO3(s) + Na2SO4(aq)

Equation for gas-evolving reaction (part 3):

NaHCO3(aq) + KHC4H4O6(aq) → KNaC4H4O6(aq) + H2O + CO2(g)

(This is actually a 2 step reaction.)

Special safety concerns for Lab 9:

  • Be sure to wear gloves and goggles this week.
  • Alcohol is flammable, so please keep it away from any sources of heat or sparks.
  • If anything spills, please clean it up immediately with a paper towel and let your instructor know.
  • If glass breaks, do not pick it up with your bare hands. Notify your instructor immediately.
  • Be sure to wash your hands when you are finished with this lab.

Materials:

Part 1, see list page 75. Add clock/watch and cotton swabs (to clean wells).

Part 2: 

  • Magnesium sulfate (Epsom salt)
  • Sodium carbonate (made by heating baking soda)
  • Water
  • 2 clear plastic cups
  • 2 small paper cups for weighing
  • Scale
  • Stirring rods
  • Measuring spoons
  • Graduated cylinders

Part 3:

  • Sodium bicarbonate (unheated baking soda)
  • Potassium bitartrate (Cream of tartar)
  • Water
  • 2 small paper cups for weighing
  • Beaker or clear plastic cup
  • Plastic wrap – piece to cover beaker or plastic cup

Procedures:

Part 1. Session III-3 Single Replacement Reaction

Go ahead and write down the Procedure on pages 75-76 the lab manual with these adjustments:

Step 2. Add:  Take the temperature of the copper (II) sulfate solution and record it.

Step 4. It turns out to be very important to use exactly the same amount in each well of the reaction plate, or you won’t be able to see the color differences (more material means darker color). Also, try not to pick up and transfer any bits of iron with the pipette.

Step 5. Add:  Check the temperature of the copper (II) sulfate solution again. Any changes?

Be sure to leave room in your notebook to record the temperature, amounts of materials used, observations, etc.

Part 2:  Double-displacement/precipitation reaction

Obtain the materials listed above

1. Pour 100 mL of water in one clear plastic cup. Weigh 10 g (about 1 tablespoon) of magnesium sulfate into a paper cup (remember to tare). Add to the water and stir until the solution is clear.

2. Pour 50 mL of water in another clear plastic cup. Weigh 5 g (about 1 teaspoon) of sodium carbonate into a paper cup. Add to the 50 mL of water and stir until the solution is clear.

3. Once both solutions are prepared and clear, pour the sodium carbonate solution into the magnesium sulfate solution.

Record your observations:

Part 3:  Gas evolving reaction

1. Weigh 6 g of sodium bicarbonate (baking soda) into a small paper cup, using the scale.

2. Weigh 4.5 g of potassium bitartrate (Cream of tartar) into a paper cup, using the scale.

3. Add 100 mL water to a clean beaker or clear plastic cup. Add the two powders you weighed out to the water and then cover the cup or beaker quickly with a piece of plastic wrap.

Record your observations:

Conclusions:

Once you have completed all three parts, sit down and write a sentence or two to explain the results.

Discussion:

Record any thoughts you have about the experiments, including:

  • Possible improvements to the procedures or how to tweak techniques
  • How the results differed from your expectations
  • Whether the goals were met
  • Suggestions for other experiments
  • The answers to the review questions he provides on page 76.

Please leave a comment or send an e-mail if you have any questions before our meeting.

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