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?

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

Answer 1

The student's reasoning is incorrect because water can dissolve ionic compounds. The solubility of an ionic compound in water depends on various factors and solubility rules, and therefore, not dissolving in water is not conclusive proof that a substance is ionic. The correct option is a.

Step-by-step explanation:

The student wants to determine whether an unknown solid is an ionic compound by checking if it dissolves in water. The student has observed that the solid does not dissolve and believes this proves the solid is ionic.

This reasoning is not correct. The best evaluation of the student's reasoning is (a) He is incorrect because water can dissolve ionic solids.

Water, being a polar solvent with a high dielectric constant, can dissolve many ionic compounds due to its ability to stabilize the ions in solution through ion-dipole interactions.

Even though an ionic compound might not dissolve in water, it does not necessarily indicate that the compound is not ionic. Some ionic compounds are insoluble or only slightly soluble in water, but it does not mean they are completely non-ionic.

The solubility depends on a balance of lattice energy within the solid and hydration energy when it dissolves. Solubility rules can help predict whether an ionic compound will dissolve in water. The correct option is a.