Experiment 4: Elements and Compounds There are over 100 known elements, each unique in its own way. These elements can theoretically combine together to create an infinite number of compounds. These compounds are almost always significantly different from the elements from which they were formed. Consider such toxic elements as sodium and chlorine, which combine to form sodium chloride, a compound essential for life. In this experiment you will have the opportunity to take a tour of some of the more common elements, examine their properties, and learn how to identify their presence in a solution. PROCEDURE A. Instructor Demonstration: The Electrolysis of Water a. Set-up an apparatus designed to pass electricity through water. b. Apply a small voltage across the water. Observe the results. c. Increase the voltage. Observe any changes. d. After the apparatus has run for some time, compare the amount of gas in each tube. B. Instructor Demonstration: Sodium Chloride vs. Sodium Metal a. Observe sodium chloride and sodium metal. How are they similar? How are they different? b. To a beaker of water, add a few drops of phenolthalein indicator. Observe the color. Now, add a small sample of sodium chloride. Observe any significant changes. c. Add a few drops of water to a different beaker of water. Now, carefully add a small piece of sodium metal to the water. Observe any changes. C. Sublimation of Iodine a. Set up a ring stand and wire gauze. Put a Bunsen burner under the gauze, but do not light it yet. b. Add a small amount (about 1 gram) of solid iodine (I2) to a 250 mL or 400 mL beaker. This beaker must be dry or it may be ruined by this experiment! c. Take your evaporating dish and fill it with ice. Then, cover the top of the beaker with the evaporating dish. The bottom of the dish must totally cover the opening of the beaker. d. Light your Bunsen burner, and gently heat the bottom of the beaker. Do not continue heating after the iodine has sublimed. e. Record your observations on the report sheet. D. Reaction of Potassium Iodide with Lead (II) Nitrate a. Measure out between 1 and 2 mL of potassium iodide (KI) solution into one test tube; measure out between 1 and 2 mL of lead (II) nitrate solution—Pb(NO3)2—into another test tube. b. Pour the contents of one test tube into the other. c. Record your observations on the report sheet. E. Flame Tests a. Fill each of seven wells in a spot plate with one of the solutions provided. Each solution contains a different ion: sodium(Na), potassium(K), lithium(Li), copper (Cu), calcium(Ca), barium(Ba), and strontium(Sr). Be sure to keep track of which well contains which ion. b. Take a platinum wire, and dip into distilled water to clean it. Then, dip into one of the solutions in the spot plate. Place the wet wire in the hottest part of a Bunsen burner flame. Do not put the glass portion of the wire holder in the flame. Observe and record your observations. c. Clean the wire by rinsing it with distilled water, then dipping it in 1 M hydrochloric acid (HCl), and finally by rinsing with distilled water again. Caution: hydrochloric acid can cause severe burns! d. Repeat this procedure for the remaining solutions. F. Elements a. Samples of several elements have been placed around the room. Provide a visual inspection of each one on the report sheet.

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Report Sheet

Name ____________________

Elements and Compounds A. Electrolysis of Water a. What did you observe when voltage was applied to the water? What changes occurred when the voltage was increased?

b. Compare the difference in the volume of gas in each tube. One of the tubes contains hydrogen gas, the other oxygen. Which tube contains which gas? [Hint: think about the chemical formula of water]

B. Sodium Chloride vs. Sodium Metal a. Description of sodium chloride

b. Description of sodium metal

c. What happened when sodium chloride was added to water?

d. What happened when sodium metal was added to water?

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e. Based on these observations, should one assume that sodium and its compounds (like sodium chloride) will always have similar chemical and physical properties?

C. Sublimation of Iodine a. Describe what you observed in the beaker after the iodine was heated.

b. Did you observe a physical change or a chemical change? Explain how you came to this conclusion.

D. Reaction of Potassium Iodide with Lead (II) Nitrate a. What did you observe when the solutions were mixed?

b. Was this a chemical change or a physical change?

c. Is the color of the product a physical property or a chemical property?

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E. Flame Tests a. Describe the color of light given off by each of the six solutions. sodium:

potassium:

lithium:

copper (II):

calcium:

barium:

strontium:

b. Based on your observations, can we assume that it is always possible to identify an element with a flame test, using only our eyes to assist us? Explain.

F. Elements a. Briefly describe the physical properties of each of the elements below. copper:

mercury:

sulfur:

phosphorus:

oxygen:

nickel:

carbon:

zinc:

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Materials for this lab: For the instructor: Apparatus for electrolysis of water (with acidified water) Three 800-mL beakers Small samples (< 10 g) of sodium chloride and sodium metal(in oil) Phenolthalein solution in a small dropper bottle For the class: 3 small bottles of each of the following solids: iodine potassium iodide lead (II) nitrate dropper bottles containing 0.2 M solutions of each of the following (for flame tests) NaCl, LiCl, KCl, CuCl2, BaCl2, CaCl2, SrCl2 platinum wire 1 M HCl dipping solution to clean wires ice Samples of these elements for viewing: copper, mercury, sulfur, phosphorus (both allotropes), oxygen, nickel, carbon, zinc

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