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    Could someone please explain how when Magnesium or Beryllium reacts with water, the hydroxides formed only remain on the upper surface of the metal and not around the entire solid?

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    Both beryllium hydroxide ans magnesium hydroxide are only sparingly soluble in water. When either metal is reacted with water its hydroxide forms at its' surface (because that is where the water molecules and metal atoms are in contact). The vast majority of the hydroxide formed does not dissolve, so a metal hydroxide layer forms all over the metal surface - the prevents water molecules being able to react with the unreacted metal atoms below that layer.

    Other group 2 hydroxides are more soluble in water, meaning the hydroxide layer dissolves. This allows water molecules to react with the entire piece of calcium for example.
 
 
 
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Updated: October 7, 2017
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