Double Displacement Reaction help and explanation

Question

__NaOH+__CaCl2 --> __?__+__?__

Answer 1

Na and OH are together and Ca and Cl₂ are together (on the reactant side). A double replacement means they both change partners. So (on the product side) you would have Na hook up with Cl₂ and Ca hook up with OH. BUT, the charges won't match so we need to tweak them. Since Na has a plus 1 charge it would need only one Cl to match up (Cl has a minus 1 charge). And Ca has a plus 2 charge so it needs 2 OH ions to match up (each OH has a minus 1 charge. Making the (still unbalanced) chemical reaction equation:

NaOH + CaCl₂ → Ca(OH)₂ + NaCl

To balance this we must add coefficients to give us the same numbers of atoms on each side:

2NaOH + CaCl₂ → Ca(OH)₂ + 2NaCl