[Mrs. G]

I have a student who needs to be able to identify calcium hydroxide, aluminum hydroxide, and zinc hydroxide. She only wants to use sodium hydroxide as the only reagent. Any ideas?? Thanks.

[Donaldson Tan]

Only Ca(OH)2 remains undissolved in excess aq. NaOH.

Only Zn(OH)2 turns yellow when heated, and returns to colourless upon cooled.

Al(OH)3 can be identified by its failure to produce the two abovementioned observations.