Lets say you are tesing for Al3+ ion and you add a few drops of NaOH to Al3+. What is the white preciptate that forms? Na or Al(OH)3? I'm curious to know, Na is an element, so is it soluble in water? Thanks all.
Originally posted by anpanman:Lets say you are tesing for Al3+ ion and you add a few drops of NaOH to Al3+. What is the white preciptate that forms? Na or Al(OH)3? I'm curious to know, Na is an element, so is it soluble in water? Thanks all.
Na itself is not soluble in water, ie. you don't write Na(aq).
To be precise, Na(s) reacts in a redox reaction with water, to form soluble products of Na+ cation, OH- anion, and hydrogen gas.
Na(s) --> Na+(aq) + e-
Na+(aq) is soluble in water.
In the reaction you described, it is the OH-(aq) that precipitates out with Al3+(aq) to form Al(OH)3(s), a white ppt.
Adding excess NaOH(aq), you form the complex ion [Al(OH)4]-, which is soluble in water (due to favourable ion-dipole interactions).