Science Core Experiments Directory | Science Home Page | Curriculum Home Page | USOE Home Page

Copyright © by the Utah State Office of Education.

Differences Between Ionic and Covalent Compounds

Description of Activity

Title: Differences Between Ionic and Covalent Compounds.
Overview: Students will observe some of the differences in macroscopic properties between ionic and covalent compounds. In particular, they compare solubility in water, solubility in methanol, relative melting points, and solution conductivity.
Duration: One 45 Minute lab period.
Materials:

24 well micro plates			benzoic acid, (C6H5COOH)
wood splints				magnesium chloride, (MgCl2)
100-mL beakers				petrolatum (vaseline)
micro scale conductivity testers	potassium iodide (KI)
scoopula				sodium sulfate (Na2SO4)
forceps					sucrose (C12H22O11)
					methanol CH3OH
					distilled water

Background

Properties such as melting point, boiling point, solubility, electrical conductivity, color, and odor can help you distinguish ionic from covalent compounds. As in many areas of chemistry, the distinctions are not always clear, nor do the distinctions apply to all compounds.

Teaching and Learning Strategies

Using micro plates is an easy way for student to find relative solubility, but students must understand just how small a Ògrain-of-riceÓ is. If too much solid is used, students may not see whether or not there is dissolving.

The relative melting point procedure should be done in the fume hood. Arrange similar sized samples of each chemical on the blade of a large spatula. Light a burner and hold the spatula blade above the tip of the flame so that it is slowly heated. Observe the order of melting. If a sample takes more than a minute to melt, have student record "did not melt in one minute" on their data table. This procedure could possibly be a teacher demonstration.

Prerequisite Instruction

Students are being asked to make distinctions between ionic and covalent compounds based first on their formulas, then on their properties. A general discussion of the bonding differences would be worthwhile.

Invitation to Learn

Observe some properties of several ionic and covalent compounds and recognize patterns among those properties. Use what you learned from your observations to distinguish ionic compounds from covalent compounds.

Procedure

1. Using a wood splint for the petrolatum and a scoopula or forceps for the other chemicals, put a sample about the size of a pea of each of the chemicals on a sheet of paper. Label the samples.
2. Place a "grain-of-rice" size sample of each solid in 6 wells on the micro plate. Add water to each well. Stir and observe the relative solubility of each solid.
3. Repeat the solubility test using methanol as a solvent.
4. To test for conductivity first dissolve each solid in half methanol and half water. Test the resulting solutions with the conductivity tester.
5. Test the samples for relative melting points as instructed by your teacher.

Safe Operating Procedures

The methanol should be provided only in small quantities. Be sure there are no open flames in the lab while students are using the methanol and be sure that all other containers of methanol are stored away from the lab.

Use only micro scale conductivity tests that are powered by 9-volt transistor batteries or by one or more 1.5 volt flashlight batteries.

Summary of Learning

Analysis and Conclusions

1. Determine, based on the formula, whether each of the substances used is covalent or ionic.
2. Look carefully at your results. Do you see any patterns? Summarize your results.
3. Make generalizations on the solubility, conductivity, and melting point for both covalent and ionic bonds.
4. Explain the reason why you tested electrical conductivity with a solution containing both methanol and water.
5. Predict the following, based on the patterns established in this experiment:

A. solubility of sodium iodide (NaI) in water.
B. relative melting point of sodium iodide.
C. electrical conductivity of glucose, C6H12O6, in water.

2 multiple choice questions

1. Why does tap water conduct electricity but distilled water does not?

a. Distilled water must have covalently bonded substances dissolved in it.
b. Distilled water must have ionicly bonded substances dissolved in it.
c. Tap water must have covalently bonded substances dissolved in it.
d. Tap water must have ionicly bonded substances dissolved in it.

2. When comparing melting points between ionic and covalent substances

a. No trends or generalities can be found.
b. Ionic compounds melt at lower temperatures than covalent compounds.
c. Ionic compounds melt at higher temperatures than covalent compounds.
d. Impossible to compare because covalent compounds burn before they melt.

All rights reserved except those which may be granted under Sections 107 and 108 of the Copyright Revision Act of 1976. This document may be freely distributed in its entirety for non-profit purposes provided that the copyright notice is not removed. If you have questions concerning proper use of this material, or if you are interested in obtaining permission, contact the Curriculum Section Reception Desk at 801-538-7698.

This document was submitted for posting to the Internet by the State Science Specialist. Any questions concerning content should be directed to that individual.

Updated September 26 1997 by Michelle Dumas