Chapter U4.70, Problem 2E

Interpretation Introduction

Interpretation:

The reason due to which dissolving can be described as either a physical or chemical change must be explained.

Concept introduction:

Dissolving is a process in which a solute is homogeneously distributed within the solvent making a solution.

Answer to Problem 2E

In some cases, dissolving is a physical change and in some cases, dissolving is a chemical change.

Explanation of Solution

Many dissolution processes are an example of physical change in which no change in chemical properties takes place. For example, when sugar is dissolved in water, then solid sugar forms a homogeneous mixture in water via the formation of hydrogen bonds with water.

In some cases, dissolution takes place via the formation of soluble ions or complex.

For example, gold forms soluble complex ion with NaCN in the presence of oxygen and water.

The reaction is represented as follows:

  ${\text{Au+4NaCN+O}}_{\text{2}}{\text{+2H}}_{\text{2}}\text{O}\to \text{2Na}\left[\text{Au}{\left(\text{CN}\right)}_{\text{2}}\right]{\text{+2NaOH+H}}_{\text{2}}{\text{O}}_{\text{2}}$

This is a chemical change.

Conclusion

Thus, dissolving can be a physical or chemical change.