Experiment for Glencoe Chapters 8 & 9:
Comparing Covalent and Ionic Solids

Introduction:

A compound is defined as the chemical combination of two or more elements.  A chemical bond is the "glue" that holds atoms of different elements together.  Bonds can generally be classified into two general types: ionic and covalent.  Ionic bonds generally occur between a metallic atom and a nonmetallic atom.  The ionic bond involves the transfer of electron from the metallic atom to the nonmetallic atom, resulting in ions (positively and negatively charged).  The positively charged metal ion is attracted to the negatively charged nonmetal ion.  Covalent bonding involves the sharing of electron and generally occurs between atoms that are nonmetallic.

Properties such as melting point, boiling point, solubility, electrical conductivity, color and odor can help you distinguish ionic from covalent compounds.  In this experiment, you will observe several properties of some ionic and covalent compounds and attempt to recognize some patters among the properties.  It is important that you understand that the patters are generalizations that do not necessarily apply to all ionic and covalent compounds.

Experiment Objectives:

1. Observe and record the solubility, melting time, and electrical conductivity of several ionic and covalent compounds.
2. Recognize patterns in the properties of compounds that can be used to distinguish ionic compounds from covalent compounds.
3. Use the patterns in the properties of substances to predict whether they are primarily ionic or covalent compounds.
4. Identify compounds as either primarily ionic or covalent from the name and formula.

Materials:

• test tubes with stoppers and rack
• weighing paper
• wash bottles with distilled water
• hot plate
• beaker
• chemicals
  • stearic acid (also known as stearin and used to make dripless candles)
  • calcium chloride
  • paradichlorobenzene (also known as moth balls)
  • ascorbic acid (also known as vitamin C)
  • potassium nitrate
  • sodium hydroxide - CAUSTIC - BE EXTRAORDINARILY CAREFUL!
  • dextrose (type of a sugar)
  • sodium bicarbonate (also known as baking soda)
  • unknowns A and B

Procedure:

Part I: SOLUBILITY in distilled water or hot water

1. Put on lab aprons and goggles - NEVER REMOVE GOGGLES while inside the lab.
2. Heat approximately 150 mL of tap water on the hot plate.  This will be your water bath that you will use to help determine the solubility of each substance in hot water.  Do not let your water boil....keep it simmering.
3. For each chemical that you test, put a "pea size" amount of substance onto a piece of weighing paper.
4. Using the weighing paper, slightly roll the paper and pour the solid crystals into the test tube.
5. Add about an inch or so high of distilled water (from the wash bottles) in a test tube.
6. Use a rubber stopper and then shake for whatever period of time you need to ensure maximum dissolving.  Remove stopper before placing test tube in the water bath.
   • NOTE: If the substance has completely dissolved just by shaking, you do NOT need to place it into the water bath.  Only do this step if the substance does not initially dissolve.
7. Look carefully at the solution.  Determine the solubility of each substance.  Record your data on the data sheet you created.
   • S = soluble (No crystal is visible in the solution and the solid has completely dissolved.)
   • PS = partially soluble (Some crystal is still visible or the solution looks cloudy.)
   • NS = not soluble (Crystals sit at the bottom of the solution or solid floats on the top of the water.)
8. Dispose of all substances that DISSOLVED down the sink.  Dispose of all substances that DIDN'T DISSOLVE in the trash.
9. Thoroughly rinse test tubes, make sure they are clean and then put back into test tube rack upside down to drain!  
10. Return the cleaned test tubes and rack up to the front lab demo area.
11. Return the cleaned rubber stoppers up to the front lab demo area in the container provided.

Part II: MELTING TIME

1. The teacher will demonstrate melting time of each solid.  
2. Record your data on the data sheet you created.

Part III: ELECTRICAL CONDUCTIVITY

1. The teacher will use a conductivity tester to demonstrate the electrical conductivity of each solid.  The solid samples will be placed into distilled water, mixed thoroughly and then tested.
2. Electrodes are placed into the solution and the tester is turned on.  If the solution conducts electricity, the light bulb will light up and the substance is a good conductor.   If the solution does not conduct electricity, the light will not go on and the substance is a non-conductor.  If the light bulb is dim, the solution is considered a poor conductor.
3. Record for each sample on the data sheet you created.
   • GC = good conductor (light bulb lights up brightly)
   • PC = poor conductor (light bulb barely lights up)
   • NC = non-conductor (light bulb doesn't light up at all)

Data Table:

Print off this DATA TABLE.

Lab Report:

Work on the lab in class in groups; however, all lab reports are to be done individually.

    For the data table...

1. Look carefully at the data you collected.  Determine whether each compound is ionic or covalent.  Write this information in the appropriate column on your data table.  Be sure to do this as well for your two unknowns.
2. Complete the column heading for chemical formula for each substance (except for the two unknowns).  For some substances, you may need to look up in a reference book or google the correct chemical formula.

    For the experimental analysis ...

This ANALYSIS section of the lab report is the real "meat" of this experiment (the most important!).  In your explanations, you need to be constantly THINKING about the relationship between the title of the experiment and the data you collected.  You need to THINK about what you have recently learned about the nature of ionic and covalent compounds and what makes them clearly distinct from each other.  When you are asked to explain your answer, be sure to explain why you see what you see in terms of the data you are analyzing.

Click here to see the grading rubric for this part of the lab writeup.

WORD PROCESS this information below and put into paragraph form with appropriate subheadings for each question.  Complete each question in order.  Be sure to relate what patterns you have found to the type of compounds you tested in all answers!  

1. Are there any patterns apparent in the solubility data?  Explain WHY. (As you explain WHY, you MUST be relating your information to your data using ionic vs. covalent compounds.)
2. Are there any patterns apparent in the melting time data?  Explain WHY. (As you explain WHY, you MUST be relating your information to your data using ionic vs. covalent compounds.)
3. Are there any patterns apparent in the conductivity data?  Explain WHY. (As you explain WHY, you MUST be relating your information to your data using ionic vs. covalent compounds.)
4. Predict (and explain why!) the solubility, melting time, electrical conductivity and type of compound for:
   • sodium iodide
   • magnesium nitrate
   • fructose
   • table salt

What you will turn in stapled together:

• Completed Data Table
• Experimental Analysis -word processed!