Question

Please help me answer the question:

What does it mean Write a net ionic equation for the reaction

2HCl + Ca(OH)2 -> CaCl2 + 2H20

Answer 1

A net ionic equation consists of the ions that react; the spectator ions are not present. First, write what you have done in ionic form. I assume both HCl and Ca(OH)2 are aqueous solutions.
2H^+ + 2Cl^- + Ca^+2 + 2OH^- ==> Ca^+2 + 2Cl^- + 2H2O.
The rules for doing this are:
Write as molecules
a. gases
b. precipitates (insoluble materials).
c. weak electrolytes.
I simply looked at HCl, said it is soluble, it is a strong electrolyte, it is not a gas; therefore, I wrote it as ions. Same for Ca(OH)2 and CaCl2. But H2O is a weak electrolyte; therefore, I wrote it as a molecule. Now, this is what you have (just copying the ionic equation here).
2H^+ + 2Cl^- + Ca^+2 + 2OH^- ==> Ca^+2 + 2Cl^- + 2H2O.

Now cancel those ions common to both sides. I see 2Cl^- on both sides so cancel them. I see Ca^+2 on both sides so cancel them. What does that leave?
2H^+ + 2OH^- ==> 2H2O. Of course we can reduce the equation by dividing the coefficients by 2 to obtain
H^+ + OH^- ==> H2O and that is the net ionic equation. The Ca^+2 and Cl^- are spectator ions; they never entered into the reaction.