Need explanation: In ionizing bases, the reaction of sodium hydroxide in water is Ca(OH)2 (s) = Ca2+(aq)+2OH-(aq) First of all, how do I know that Ca(OH)2 is sodium hydroxide? Is this something I need to just know? I don't know where the parentheses and the 2 came from. Secondly, how does the Ca have a 2 on it? I understand that the OH is multiplied by 2, but I don't know what reaction caused the Ca to have 2 ions.