MnSTEP Teaching Activity Collection > MnSTEP Activities > Using Properties to Identify Ionic and Molecular Compounds

Using Properties to Identify Ionic and Molecular Compounds

Tamara Ellsworth, Parkers Prairie High School, Parkers Prairie, MN, based on a lab for pre-ap chemistry at the westlake high school website.

Summary

In this high school chemistry lab activity, students will be given a several samples of compounds which they will test. It is a guided inquiry in which students will be testing different physical properties, such as melting point, or conductivity to help them determine whether the compounds are ionic or molecular. At this point of the year, they already have studied the different types of matter (solutions, compounds, mixtures, etc.), and the Periodic Table trends. And they are about to learn about ionic and covalent bonding. This activity will help students make connections between the two types of compounds with the Periodic Table and will help bridge in to the nomenclature of ionic and molecular compounds.

Learning Goals

This activity is designed for students to test the physical properties of their choice to help them group the chemicals into ionic and covalent compounds categories. The students will write procedures for five different tests in which they will perform in which the teacher will approve of. The students will construct data tables with different compounds and the qualitative tests performed. From this information students will analyze their results to determine whether the compounds or mixtures are covalent or molecular compounds. Some of the skills students will do: observing, safe and clean lab practices, different waste disposal, repeat testing, defend their choices with oral discussions, and answering higher order questions. The key concept for students to learn in this activity is being able to determine what physical properties exist in an ionic or a molecular compound. Students will have to know terms of ionic compound, ionic bond, covalent bond and molecular compound.

Context for Use

This lab would be ideal for lab teams of 2, 3, or 4—depending on class size. It will take a maximum of 3 fifty minute class periods. "White boards" in this lab are actually 2' x 1.5' pieces of melamine laminate boards which each group will use dry erase markers to display properties for discussion. Large pieces of paper would work in place of the white boards.

Subject: Chemistry:General Chemistry:Bonding & Molecules
Resource Type: Activities:Lab Activity
Grade Level: High School (9-12)

Description and Teaching Materials

Inquiry Lab: Using Properties to Identify Ionic and Covalent Compounds

Team Brainstorming Exercise:
What are some physical properties?
Write 6 properties on your white boards for discussion.

Look at the containers of: sodium chloride, potassium iodide, sucrose, benzoic acid, camphor, sodium nitrate, tap water, distilled water, 3M Hydrochloric acid and paint thinner.

Choose the five properties you would like to test of each of chemical.

Procedures
Each team member: In your ChemJournal write the procedure you will need to follow to test your chemicals. Plus, you need to decide which chemicals you want to test so you can form a high quality analysis and conclusion. Please separate the different procedures in your writing. Procedures must be approved before you can begin any testing... ANY TESTING!!!!
NOTE: Any paint thinner mixtures must be disposed in the "Paint Thinner Waste" Container in the hood. All benzoic acid & camphor waste must be placed in garbage can in front of the classroom with the garbage bag. All other mixtures may be flushed down the drain with water.

Data Table(s)
In your ChemJournal set up data table(s). Please explain if abbreviations are used in the data table, e.g. "IS" means insoluble. Make it neat and easy to understand.
NOTE: make room for an extra column at the right side for "further studies". After the lab is completed and analyzed we need to group or identify the chemicals. Your teacher will advise you what to label this column at that time.

Data Analysis
With your team try to find a way to group your chemicals into two categories. List them on the white board and be prepared to explain how your team made these decisions.

Information about two types of compounds
- An ionic compound is a compound that has an ionic bond. An Ionic bond is a type of chemical bond that involves a metal and a non-metal ion. The bond is formed by an attraction between tow oppositely charged ions. It is a bond where the electron(s) are transferred from one atom to another
- A molecular compound is a compound that has a covalent bond. A covalent bond is a chemical bond that involves non-metal ion and a non-metal ion. The bond is formed by two atoms sharing electron(s)

Conclusion And Questions
a) In your conclusion discuss in writing ALL of the evidence (of all 5 tests). Then after reading the information about compounds, conclude with your team if each compound is ionic or covalent, or is it more in between. Document this information in the last column of your data table. Then (in your conclusion) compare your findings for each compound with what you now know about the ionic vs. covalent nature of each compound. Make sure this information is clear in your conclusion.
b) List the physical properties that indicate ionic bonding exists in a compound.
c) List the physical properties that indicate covalent bonding exists in a compound.
d) Is there any one property that best indicates whether a compound is molecular or ionic? Explain.
e) Find a relationship between the volatility of a substance and its type of bond.
f) Does the strength of a bond have anything to do with the melting point? Explain.
g) Why can ionic compounds conduct electricity but covalent compounds cannot?
h) If a compound is not soluble in water (does not dissolve in water), is there a possibility that it will conduct electricity? Explain.
i) Sodium nitrate has several covalent bonds, yet the substance has primarily ionic character. How can this be possible? (Hint: think about the specific ions that make up the compound.)

Other Conclusion Questions to explore or answer:
1. Water molecules are polar which means one side of the molecule is positively charged and the other side of the molecule is negatively charged. Which substances tend to dissolve easier in water, ionic or covalent? Why?
2. Explain the difference in conductivity of tap water and distilled water.

Teaching Notes and Tips

I've always had my students do a variation of this lab where I tell them what properties they will test and how to test them. This is inquiry so they will find the properties, which are common, and test them. The brainstorming discussions will help me direct the class into testing good quality physical properties. For guiding students, if necessary, tell the students to refer back to chapters about different types of matter or the Periodic Table trends to get students to think about: odor, melting point, electronegativity, Lewis-dot structures, boiling point, hardness, volatility (measure by odor), water solubility, alcohol or oil solubility and conductivity. If necessary, give containers of paint thinner, camphor, salt to each group to help them think of physical properties to test.

When testing students should list the equipment they will use in their tests, like test tubes, small beakers, spot plates, Bunsen burners with hoses, crucibles, etc. For testing, many of our schools don't have the equipment but there are other great alternatives. Boiling point would be very hard to measure with the volatility of paint thinner, and the extreme temperatures of all compounds—steer students away from the boiling point. Melting point would not be impossible without proper equipment, use a crucible and measure the amount of time it takes to melt (if it does). The longer the time period means the higher the melting point. Volatility is measured by odor. The particles in a volatile compound must be held together by weaker forces so that some can break away and travel through the air to our noses. Hardness is measured by how malleable or brittle a compound is with a hammer and board. Conductivity my students have experience with conductivity during the periodic table unit. Conductivity can be measured with a meter or a homemade circuit.

The data table must have an empty column at the right. Later, it will be titled "ionic or covalent".

If all the groups don't do enough quality tests for determining covalent and ionic compounds, have them fill in their data in an excel worksheet for all to view on the projector.

Wait until all the data has been collected and students categorize their data before handing them the definitions of ionic and covalent bonds and also ionic and molecular compounds then they can discuss all their evidence and write it in their conclusion.

Waste procedures are mentioned in the lab sheet—all are easy to take care of. If you need to--skip paint thinner.

Assessment

In a MnSTEP teaching inquiry class we used the white boards for discussion frequently. It helps the teachers/facilitators see if students are on track or not. They showed misconceptions. And the white boards could be used as a formative assessment. The main part of this grade will be a rubric for their data tables and their conclusions with questions.

Standards

Minnesota 2009 Standard: 9C.2.1.2.1 Explain how elements combine to form compounds through ionic and covalent bonding.

References and Resources

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