Question

A precipitate forms when a small amount of sodium hydroxide is added to a solution of aluminum sulfate. This precipitate dissolves when more sodium hydroxide is added. Explain what is happening.

Answer 1

3NaOH + Al2(SO4)3 -> 3Na+ So4-2 Al+3 3OH-

As you can see form the equation, when you add those substance you will have those ions

Now:

Al+3 and 3OH- <-> Al(OH)3 (s)

which is solid (the precipitate)

This doesn't mean that all Al+3 will precipitate, actually many of Al+3 will remain in solution.

If you add even more NaOH, tha tis more OH- ions

You are going to force the precipitation:

Al+3 and 3OH- <-> Al(OH)3 (s)

even MORE OH, MORE Al+3 precipitates as Al(OH)3