[MustangFTW]

Hi


I have a couple questions that ive had trouble understanding.

1. How do we know what ions are produced when say, ZnCl2 is dissolved in water? First thing i think of is ZnCl2 ----> Zn+Cl2 but its actually Zn+2Cl, why do we write the 2 as a coefficiant rather then keeping it as a subscript? is it because Chlorine doesnt have a reason to bond to another Chlorine? there are some like (NH₄)₂SO₄ where the 4 in the SO₄ stays as a subscript, when do we do bring the subscript up?

2. a question on mu homework is asking to write a balanced net ionic equation for CaCl₂ and Cs₃PO₄, for this i need to know which is the reactant ion, how would i know which is the reactant ion and which is the spectator ion?



thanks.

[Arkcon]

So you're having trouble determining the ionic equation, and want to know why its not ZnCl₂ Zn+Cl₂.  But your second reaction, Zn+2Cl is also wrong, especially for an ionic equation.  Can you fix it?  Feel free to play around with the subscript and arrow buttons.  Lets see if we can solve this first one, and then work on the next problem.

[MustangFTW]

So i guess you mean i should write it as

ZnCl(aq) Zn²⁺ (aq)+2Cl^-(aq)

[Arkcon]

Right, so you were told (or at least it was implied) than ZnCl₂ is soluble in water, the reaction ZnCl₂  Zn + Cl₂ isn't a dissolution into ions, but instead a decomposition.  You may get that reaction, if you got dry powdered ZnCl₂ hot enough.  But Zn powder doesn't dissolve in water, and Cl₂ is a choking yellow gas, that is slightly soluble in water, but would mostly just bubble free.  So I'm hoping you can separate the phenomena now.