Name Date Class

Dagnostic Properties of Bonds

The millions of chemical substances found in nature are the result of approximately 100 chemical elements bonding together. These substances can be divided into three major groups: metals; salts, or ionic compounds; and cova-lent substances, the last making up the overwhelming majority of chemicals. Metallic substances, such as copper and aluminum, hold their atoms together by communal sharing of outer electrons. Salts, such as common table salt, NaCl, have two or more charged particles, which are ions resulting from the transfer of electrons. Covalent substances, such as oxygen and water, consist of molecules held together by electron sharing. In the laboratory, these three major groups display different properties in their appearance, relative melting or boiling points, solubilities in different solvents, and ability to conduct electricity.

In this activity, you will explore differences in properties, whereby millions of substances can be classified into one of three major groups. These groups are metals, such as copper (Cu) and aluminum (Al), salts, such as potassium chloride (KCl) and potassium iodide (KI), and covalent compounds, typified by naphthalene and benzoic acid.

OBJECTIVES

  1. Make laboratory observations of six solid substances, each of which exhibits the properties of one of the three types of chemical bonds.
  2. On the basis of your observations, list the distinguishing properties of the three types of chemical bonds.

MATERIALS

Inline Figure

can lid with indentations

ring stand with ring

watch glass

deionized water

laboratory burner

chemical scoop

beaker (50 or 100 mL)

glass stirring rod

paper towel

conductivity tool

PROCEDURE

CAUTION:Some of the chemicals you will use are toxic. Follow proper chemical hygiene procedures. Wash your hands thoroughly after completing this laboratory activity.

Part 1: Appearance and Odor

  1. Obtain a very small quantity of KCl with a chemical scoop. Place it on your watch glass on the lab bench top.
  2. Describe the appearance of the solid. Notice any odor.
  3. Record your observations in Table 1 under Data and Observations. Leave the solid on the watch glass for later work.

Part 2: Effects of Heat

  1. Set up your ring stand as shown in Figure A. On the ring, place a can lid prepared with indentations.

    figure A

  2. Place in one of the indentations the same amount of KCl you used in Part 1.
  3. Light the laboratory burner and, handling the base of the burner, gently heat the underside of the can lid at the location of the solid. Observe the solid. If no change occurs, heat more intensely. If there is still no change, heat the solid from above, lightly at first then intensely. To do so, hold the burner and pass the flame over the material.
  4. Observe whether the solid melts, boils, evaporates, burns, or shows no change. Record your observations in Table 1.

Part 3: Solubility in Water

  1. Add 3 mL of deionized water to the KCl on the watch glass (from Part 1.) Stir with a glass rod and let stand about 3 minutes.
  2. Compare the remaining undissolved solid with the original quantity. Decide whether the solid is soluble (most dissolved in the water), insoluble (most remains at the center bottom of the glass) or partly soluble (some remains undissolved).
  3. Record your observations in Table 1. Save the watch glass and solution or water and solid for the next procedure.

Part 4: Conductivity of Water Solutions

  1. Pour 10 to 20 mL of deionized water into a beaker. Place the prongs of your conductivity tool into the water.
  2. Deionized water should show little or no conductivity. Depending on the sensitivity of your conductivity tool, the light indicator should be off, blinking, or dimly lit. Record your observation on the line under Data and Observations.
  3. As shown in Figure B, place the prongs of the conductivity tool in the liquid portion on the watch glass from Part 3. Observe the light indicator. Record the conductivity of the liquid as none, low, moderate, or high.

    figure B

  4. Wipe the prongs with a paper towel, immerse in the beaker of deionized water, and wipe again. Set aside the conductivity tool for the next solid to be tested. Discard the water solution or solvent-solid mix according to your teacher's instructions.

Part 5: Solubility in Paint Thinner

  1. CAUTION:This test must be performed in the fume hood because of the volatility and flammability of the solvent.
  2. Repeat the solubility test as in Part 3, using paint thinner as the solvent instead of water.
  3. Record in Table 1 whether the solid is soluble, insoluble, or partly soluble in paint thinner.
  4. Discard the solution or solvent-solid mix into the appropriate container in the fume hood.

    Repeat Parts 1 through 5 for each of the remaining five solids and complete Table 1.

DATA AND OBSERVATIONS

Conductivity of pure water


Table 1

Observations of Solids
Solid Appearance/ odor Effects of heating Solubility in water Conductivity of water solution Solubility in paint thinner
KCl          
KI          
Al          
Cu          
Benzoic acid          
Naphthalene          

ANALYSIS

  1. Complete Table 2, using the observations you recorded in Table 1. Use the words high, low, or none to compare the properties of the three bonding types.

    Table 2

    Comparison of Relative Properties
    Bond type Melting point Solubility in water Conductivity of water solution Solubility in paint thinner
    Metallic        
    Ionic        
    Covalent        

  2. Which solid has the highest melting point?


  3. Which solid has the lowest melting point?


CONCLUSIONS

  1. Which chemical bond type is found in substances with high melting point, water solubility, and aqueous conductivity?


  2. Which bond type is found in substances that have low melting point, are flammable, and tend to dissolve in nonpolar solvents?


  3. Which bond type is found in substances that have luster and are insoluble in water and nonpolar solvents?


  4. Most of the changes you observed in this experiment are considered physical, except for burning, which is a chemical change. The formula for naphthalene is C10H8. Write a combustion equation for the complete reaction of naphthalene with oxygen in air to form carbon dioxide and water. Indicate whether each reactant and product is a solid (s), liquid (1), or gas (g).


  5. Consider chemical substances in your daily life, or look for examples in your chemistry book. In the table below, list two more examples of each of the three bonding types.
    Ionic Covalent Metallic
         
         


  6. Metals and nonmetals form substances that can be divided into three major chemical bond types. For each of the three bonding types, which types of elements—metallic or nonmetallic—bond?

    Metallic:_________________________

    Ionic:___________________________

    Covalent:________________________

EXTENSION AND APPLICATION

There are exceptions to the generalizations above, as there are to many scientific generalizations. Repeat the experiment with sugar, a covalent substance. Contrast your results with the conclusions you made above.