Metal hydroxides solubility, precipitates, colours

Some metal hydroxides forms precipitates, and some are solutions. Some hydroxide precipitates are dissolved when we add more water to the compound. Some hydroxides such as 3d metal's show different colours. Some metal hydroxides are amphoteric compounds and they react with both acids and alkalis.

Completely soluble hydroxides in water

All alkali metals hydroxides are soluble in water. Only Sr(OH)2 and Ba(OH)2 are soluble from alkaline earth metals

Completely soluble hydroides of s block metals

  • LiOH
  • NaOH
  • KOH
  • Ba(OH)2
  • Sr(OH)2

Sparingly soluble hydroxides in water

These hydroxide are dissolved when excess water is added to the precipitate. When metal hydroxide concentration is increased, it is precipitated.

  • Ca(OH)2

Completely insoluble hydroxides

3d metal hydroxides are insoluble in water. d block metals OH- show colours. Colours of precipitates are noted with respective compound. Colours of these 3d metal hydroxides can be used to identify the 3d metal.

Insoluble 3d metal hydroxides and colours

These 3d metal hydroxides are precipitates and they show different colours.

  • Fe(OH)2 - green
  • Fe(OH)3 - brown
  • Mn(OH)2 - white/pink
  • Cr(OH)3 - green
  • Ni(OH)2 - green
  • Cu(OH)2 - blue
  • Co(OH)2 - light blue
  • Zn(OH)2 - green

Other insoluble metal hydroxides

  • Be(OH)2
  • Mg(OH)2 (white)
  • Cd(OH)2 (white)

Amphoteric hydroxides of metals

Some metal hydroxides are amphoteric compounds. These hydroxides are not dissloved in water. But adding excess NaOH(aq) to these precipitates, they dissolve in the water. Also amphoteric hydroxides dissolve in dilute acids such as HCl, H2SO4. Colours of amphoteric metal hydroxides are noted with the compound.

  • Zn(OH)2 - white
  • Cr(OH)3 - green
  • Al(OH)3 - white
  • Be(OH)2 - green

Metal hydroxides solublity

This is the summary of solubility of all metal hydroxides.

solubility of metal hydroxides in water

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