Question

A student wants to determine whether an unknown solid is an ionic compound. He puts some in water and finds that it does not dissolve. He says that this proves the solid is ionic. Which best evaluates the student's reasoning?

He is incorrect, because water can dissolve ionic solids.
The test proves nothing, because water dissolves all solids.
He is correct, because polar liquids cannot dissolve ionic solids.
The test proves nothing, because it only shows that the solid is a compound.

Answer 1

He is incorrect, because water can dissolve ionic solids.

Step-by-step explanation:

I took the test.

Most ionic compounds exist as solids at room temperature. In order to melt or boil an ionic compound, the ionic bonds must be broken. Because of the strong attraction between the opposite charges, most ionic bonds are relatively strong. It takes a great deal of energy to break an ionic bond. For this reason, ionic solids have high melting and boiling points.

This strong attractive nature of ionic bonds is in part related to their ability to dissolve in solution. Those that do, may only dissolve to a small extent. For example, when sodium chloride (NaCl) is added to 100 mL of water at 0° C, we can expect 35.7 g of NaCl to dissolve. Many ionic solids will dissolve in water because of the strong attractive forces of water molecules. When solid sodium chloride (salt) dissolves in water, it separates into sodium ions and chloride ions that move about freely in the water solution. The attraction between the Na+ and Cl− ions in the solid is so strong that only highly polar solvents like water will dissolve NaCl.

Hope this helps you! :)

Answer 2

The test proves nothing, because it only shows that the solid is a compound.

That is the answer!