Problem 112 - Chemistry Matter and Change

Question

You are given two clear, colorless aqueous solutions. One solution contains an ionic compound, and one contains a covalent compound. How could you determine which is an ionic solution and which is a covalent solution? (Chapter 8)

Step-by-Step Solution

Answer

Perform a conductivity test: the ionic solution conducts electricity, whereas the covalent solution does not.

Step 1: Understand Ionic and Covalent Compounds

Ionic compounds consist of positive and negative ions held together by electrostatic forces, and they usually dissolve in water to produce electrolytes that conduct electricity. Covalent compounds, however, consist of molecules formed by covalent bonds and usually do not conduct electricity when dissolved in water because they do not form ions.

Step 2: Plan of Experiment

To distinguish between the ionic and covalent solutions, we will perform a conductivity test. A solution that conducts electricity is likely to be ionic, as it contains free ions. A solution that does not conduct electricity is likely to be covalent.

Step 3: Conductivity Test

Prepare a conductivity tester using a light bulb, wires, and electrodes. Immerse the electrodes in each solution, one at a time, to see if the light bulb lights up. If the light bulb lights up, the solution is ionic. If it does not, the solution is covalent.

Step 4: Analyze the Results

Observe which solution enables the light bulb to light up. The one in which the bulb lights up contains the ionic compound, and the other contains the covalent compound.

Key Concepts

Conductivity Test

One practical way to differentiate between ionic and covalent solutions is by using a conductivity test. This test helps determine if a solution can conduct electricity. Ionic solutions generally do this, thanks to their free-moving charged particles known as ions. On the other hand, covalent solutions typically lack these ions, so they do not conduct electricity.

To perform this experiment, you will need:

• A simple conductivity tester, which can be constructed from a light bulb, wires, and electrodes.
• Two aqueous solutions clearly marked for testing.

Immerse the electrodes into one solution at a time. If the light bulb illuminates, this indicates the presence of ions, thereby confirming the solution is ionic. Conversely, if the bulb remains unlit, you're examining a covalent solution. This straightforward experiment is a reliable indicator of the solution’s nature.

Electrolytes

Electrolytes are substances that dissolve in water to produce a solution that conducts electricity. The key players here are ionic compounds, which break down into ions upon dissolving in water. These ions, being charged particles, move freely within the solution and facilitate the flow of electric current.

Common examples of electrolytes include salts like sodium chloride ( ext{NaCl}), which disassociate into sodium ( ext{Na}^+) and chloride ( ext{Cl}^-) ions. This specific characteristic of forming ions is what allows them to conduct electricity effectively. Without these independent ions, a solution cannot conduct electricity and thus would be classified as non-electrolytic.

Ionic Bonds

Ionic bonds form between metals and non-metals due to the transfer of electrons from one atom to another. This electron transfer results in one atom becoming positively charged (cation) and another becoming negatively charged (anion).

Because of their opposite charges, these ions attract each other strongly, resulting in high melting and boiling points of ionic compounds. Some practical characteristics of ionic compounds include their crystalline structure and ability to dissolve in water, forming electrolytes. During the conductivity test, the ability of an ionic compound to conduct electricity after dissolving and disassociating into ions is a direct result of these ionic bonds.

Covalent Bonds

In contrast to ionic bonds, covalent bonds involve the sharing of electrons between atoms rather than a complete transfer. This type of bond often occurs between non-metals. Covalent compounds form molecules which do not easily break into ions in a solution.

As a result, covalent solutions do not conduct electricity, since there aren’t any free ions to carry an electric charge. For instance, a sugar solution is covalent; when dissolved in water, it doesn’t result in charged particles, and therefore won’t cause a light bulb to illuminate during a conductivity test. Covalent compounds typically have lower melting and boiling points compared to ionic compounds, signifying the weaker attractions within their molecular structure.