Describing Chemical Reactions Lab

Introduction and Purpose

In this experiment you will observe examples of the five basic types of chemical reactions. You will learn to write balanced equations, including the role of energy, to effectively communicate the chemistry of the reactions.

Procedure

Carry out the reactions using the approximate quantities of reagents suggested. Discard solutions down the drain, wash and rinse your glassware. Discard solid waste in the waste dish on the lab tables.

A. Synthesis (Combination) reaction

Reaction #1

Grasp a strip of magnesium ribbon in crucible tongs and ignite it in the burner flame. Hold it over a waste dish. Do not look directly at the flame!

Observations:

Mg + O2 MgO

Write in words:

B. Decomposition reaction:

Reaction #2

Place about 1 scoopful of solid sodium bicarbonate, (also known as sodium hydrogen carbonate) NaHCO3 into a dry test tube. Mass the test tube with the powder. Using the test tube clamp, heat the sodium bicarbonatein the test tube strongly for 2 minutes. Make sure to slant the opening of the test tube away from people. Heat the tube at the surface of the material and work down towards the bottom of the tube. Observe any changes that occur during the heating. Toward the end of the heating, light a wood splint and insert the flaming splint into the mouth of the test tube. Note what happens to the splint. Identify any odor that is readily apparent by wafting the fumes toward your nose. Caution: DO NOT sniff the test tube! Wait at least five minutes, and once the tube has cooled, mass the tube and contents again. When finished clean test tube.

Reaction #2 Observations:

NaHCO3  Na2CO3 + ______H2O + CO2 (g)

Write in words:

C. Single replacement reactions:

Reaction #3

Place a strip of copper in the SMALLtest tube with enough 0.1M AgNO3 to cover it. Set this test tube aside, and then observe the surface of the metal after 5-10 minutes. When finished, pour contents in waste dish and clean test tube.

Observations:

AgNO3 (aq) + _ Cu(s)  Ag(s) + Cu(NO3)2 (aq)

Write in words:

Reaction #4

Place a couple of pieces of zinc metal in a SMALLtest tube approximately 1/4 full of 3M HCl. Place a stopper loosely in the tube. After a few minutes, light a wood splint and insert the flaming splint into the mouth of the test tube. Hold the test tube in your hand to feel if the temperature has changed. When finished, pour contents in waste dish and clean test tube.

Observations

Zn + HCl(aq) ZnCl2(aq) + ___ H2(g)
Write in words:

D. Double replacement reactions:

Reaction #5

Add 0.1M AgNO3 to a test tube to a depth of about 2 cm. Using a new pipette add three drops of NaCl solution. Use the pipette to stir the test tube. Observe the reaction. When finished, pour or scrape using the pippete, the contents into waste dish and clean test tube.

Observations

AgNO3(aq) + ___ NaCl(aq) ___AgCl(s) + ___ NaNO3(aq)

Write in words:

Reaction #6

Place drops of AgNO3 in atest tube to a depth of about 1 cm. Using a clean new dropping pipette, squeeze full of NaOH and push to bottom of test tube and then release the NaOH. Use the pipette to stir the solution. Throw the pipette away when finished.

Observations

___AgNO3(aq) + ___NaOH(aq)  ___AgOH(s) + ___NaNO3(aq)

Write in words:

E. Combustion reactions:

Reaction #7

The teacher will perform this reaction involving ethyl alcohol (C2H5OH)

Observations—ethyl alcohol (C2H5OH)

___ C2H5OH(l) + ___O2(g) ___CO2(g) + ___ H2O(g)

Write in words:

Post Lab Analysis

  1. What are some of the observable changes that are evidence that a chemical reaction has taken place?
  1. How did the flaming splint behave when it was inserted into the tube with CO2 (g)?
  1. In what way was this different from the reaction of the H2(g) to the flaming splint?
  1. In the reaction of magnesium with oxygen gas, a considerable amount of energy was released. This is an example of an exothermic reaction. From this evidence what can you conclude about the energy stored in the reactants compared to the energy stored in the product?
  1. What other examples of exothermic reactions did you observe?
  1. Re-write the balanced equation for the reaction of Mg and O2, this time with the term “+ energy” on the appropriate side of the equation.
  1. You had to heat the NaHCO3 strongly in order for it to decompose. This is an example of an endothermic reaction. What does this tell you about the energy stored in the reactants compared to the energy stored in the product?
  1. Write the balanced equation for the decomposition of NaHCO3, this time with the term “+ energy” on the appropriate side of the equation.

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