How would you show that dissolving table salt is a physical change?

Allow the water to evaporate and recover the salt unchanged.

To show that dissolving table salt is a physical change, we need to understand the definition of a physical change and how it applies to the process of dissolving salt.

A physical change refers to a change in the state or appearance of a substance that does not involve the formation of a new substance. In other words, the chemical composition of the substance remains the same before and after the change. For example, changing the state of water from solid ice to liquid water is a physical change because the chemical composition of water molecules remains H2O throughout the process.

When table salt (sodium chloride, NaCl) dissolves in water, it undergoes a physical change. Here's how you can demonstrate it:

1. Take a beaker and measure a fixed amount of water, say 100 mL.
2. Measure a fixed amount of table salt, for example, 10 grams.
3. Add the salt to the water and stir the solution gently.
4. Observe that the salt crystals disappear, and the solution turns clear.

By doing this experiment, you can see that the process of dissolving salt in water involves a change in the state/appearance of the substances (solid salt crystals to a clear salt solution). However, there is no change in the chemical composition of either the salt or the water molecules. You have simply dispersed the individual sodium (Na+) and chloride (Cl-) ions throughout the water, creating a homogeneous mixture, but the chemical identity of the substances remains the same.

Therefore, the dissolving of table salt in water is considered a physical change.