According to the conditions of the double decomposition reaction, the blue copper sulfate solution reacts with the sodium hydroxide solution to generate sodium sulfate and copper hydroxide precipitate. Since the reaction is carried out in the solution, the generated sodium sulfate solution and blue copper hydroxide precipitate are colorless. Therefore, the reaction phenomenon should be described as: the solution becomes colorless and a blue precipitate is generated.

1. Solution color change

Before the reaction: The copper sulfate solution is blue, which is because the copper ions (Cu²⁺) in the copper sulfate appear blue in the aqueous solution. The sodium hydroxide solution is colorless.

After the reaction: When the copper sulfate solution and the sodium hydroxide solution are mixed, the color of the solution will gradually change. Because the blue copper hydroxide (Cu(OH)₂) precipitate is generated and suspended in the solution, the solution as a whole appears blue (there is also a view that the solution becomes colorless after the reaction because the generated sodium sulfate solution is colorless, and the presence of the blue precipitate makes the solution look colorless, which depends on the observation angle and the dispersion degree of the precipitate). But a more accurate description should be that a blue precipitate is generated in the solution, and as the reaction proceeds, the blue color of the solution may become lighter due to the increase of the precipitate.

2. Precipitation formation

Precipitation color: The copper hydroxide precipitate generated is blue.

Precipitation properties: Copper hydroxide is a substance that is difficult to dissolve in water, so it will form a precipitate in the solution.

3. Temperature change

Reaction heat effect: The reaction between copper sulfate solution and sodium hydroxide solution is an exothermic reaction, that is, heat is released during the reaction, causing the temperature of the solution to rise.

4. Chemical equation

The chemical equation of the reaction is: CuSO₄ + 2NaOH → Cu(OH)₂↓ + Na₂SO₄. This equation indicates that copper sulfate reacts with sodium hydroxide to generate copper hydroxide precipitate and sodium sulfate.

In summary, the phenomena of the reaction between copper sulfate solution and sodium hydroxide solution include solution color change (blue precipitate), precipitate formation (blue), temperature change (heat release causes temperature increase) and the expression of the chemical equation. These phenomena are the result of changes in the properties and states of substances during the chemical reaction.