Question

You are given two clear, colorless aqueous solutions. You are told that 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)

Short answer

To determine which solution contains the ionic compound and which contains the covalent compound, perform the following tests: 1. Test electrical conductivity - the solution that conducts electricity is likely the ionic solution. 2. Analyze the interaction with water - if a solution forms a precipitate or sediment, it could be the covalent solution. 3. Test with nonpolar solvents - if a solution mixes well with a nonpolar solvent like hexane or diethyl ether, it could be the covalent solution.

Step-by-step solution

Test Electrical Conductivity

To begin with, let's test the electrical conductivity of both solutions. Ionic compounds generally tend to be good conductors of electricity when dissolved in water. This is because they dissociate into their constituent ions which then become free to move and conduct electricity. On the other hand, covalent compounds usually do not conduct electricity when dissolved in water as they do not dissociate into charged particles. Prepare two electrodes connected to a power source and an ammeter. Place the electrodes in the first solution and observe if there is any reading on the ammeter. Repeat this process for the second solution. The solution that conducts electricity is likely the ionic solution.

Analyze the Interaction with Water

Observe the behavior of both solutions after they have been allowed to stand undisturbed for some time. Ionic compounds are typically more soluble in polar solvents like water due to their charged particles interacting with the polarity of water molecules. Covalent compounds, however, do not interact as strongly with water molecules as their molecules do not possess a charge. If one of the solutions starts to form a precipitate or sediment, that solution could be the covalent solution.

Test with Nonpolar Solvents

Another way to identify the nature of the compound is by observing their interaction with nonpolar solvents like hexane or diethyl ether. Covalent compounds, especially those that are nonpolar, tend to be more soluble in nonpolar solvents due to the "like dissolves like" concept. Take a small sample of each solution and mix it with a nonpolar solvent. If one of the solutions mixes well with the nonpolar solvent, it could be the covalent solution. By performing these tests, it is possible to identify which of the two clear, colorless aqueous solutions contains an ionic compound and which contains a covalent compound.

Key concepts

Electrical Conductivity

Electrical conductivity is a property that indicates how well a substance can carry an electric current. This is particularly useful when comparing ionic and covalent compounds in aqueous solutions.

Ionic compounds are known to exhibit good electrical conductivity when dissolved in water. This is because they dissociate into their respective ions, such as NaCl dissociating into Na extsuperscript{+} and Cl extsuperscript{-} ions. These ions are charged particles that can move freely in the solution, allowing electricity to flow.

On the contrary, covalent compounds do not typically conduct electricity in their dissolved state. This is because they do not separate into ions, thus lacking charged particles to carry an electrical current. For example, sugar dissolves in water but its molecules remain intact and neutral.

To determine if a solution contains an ionic or covalent compound, connect the solution to a circuit using electrodes attached to an ammeter. If the ammeter registers a current, the substance is likely ionic. If it doesn’t, the substance is probably covalent.

Steps include:

• Setting up a circuit with electrodes and an ammeter
• Placing electrodes in the solution
• Observing the ammeter reading

Comparing the readings from both solutions will help you identify which one contains the ionic compound.

Solubility in Water

The solubility of compounds is a key indicator of their ionic or covalent nature, especially in water, which is a polar solvent.

Ionic compounds dissolve well in water because water molecules can interact with the ions. The positively charged part of the water molecule attracts negative ions, while the negatively charged part attracts positive ions, assisting in the dissolution process. For example, when NaCl is added to water, the Na extsuperscript{+} ions are surrounded by the partial negative charge of the oxygen in water, and Cl extsuperscript{-} ions interact with the partial positive charge of the hydrogen in water.

Covalent compounds do not dissolve as readily in water as ionic compounds do. This is because covalent bonds don't break easily to form ions that can interact with water molecules. As a result, they may form a precipitate or sediment over time. For example, grease will not dissolve in water due to its covalent nature.

When examining both solutions, check for the presence of any precipitate or sediment formation over time. Lack of such behavior usually points to an ionic compound as it's more likely to remain fully dissolved.

Interactions with Nonpolar Solvents

Nonpolar solvents like hexane or ether are another means of distinguishing between ionic and covalent compounds. Nonpolar solvents have molecules that do not have a positive or negative charge and thus do not typically dissolve ionic compounds well.

Covalent compounds, especially nonpolar ones, are more compatible with nonpolar solvents. This is due to the "like dissolves like" principle, where similar polarity between solvent and solute leads to better solubility. For instance, oils and fats, which are nonpolar covalent compounds, can dissolve in a nonpolar solvent such as hexane.

To test the interaction, take separate samples of the solutions and add a nonpolar solvent. Mix them and observe:

• If the solution mixes well with the nonpolar solvent, it's likely a covalent compound.
• If it doesn't mix and instead separates, it indicates the presence of an ionic compound.

By using nonpolar solvents, you can better ascertain the nature of the compounds in the solutions.