Question

Write the balanced formula equation, complete ionic equation, and net ionic equation. If no precipitate forms, write "No reaction"
a) Hg2(NO3)2 (aq) + CuSO4 (aq)
b) Ni(NO3)2 (aq) + CaCl2 (aq)
c) K2CO3 (aq) + MgI2 (aq)
d) Na2CrO4 (aq) + AlBr3

Please explain! Thank you

Answer 1

A reaction "goes" if one of three things happen.
a. a ppt forms,
b. a gas forms, or
c. a slightly ionized substance forms.

example c.
The balanced formula equation follows:
K2CO3(aq) + MgCl2(aq) ==> MgCO3(s) +
2KCl(aq)

For the complete ionic equation you separate all of the entities above into ions UNLESS the substance meets one of the three reasons why a reaction goes to completion. For any of the three above, you write the substance as molecules and not as ions.
2K^+(aq) + CO3^2-(aq) + Mg^2+(aq) + 2Cl^-(aq) ==> MgCO3(s) + 2K^+(aq) + 2Cl^-

Then we form the NET IONIC equation by canceling those ions common to both sides. That means we cancel 2K^+(aq) and 2Cl^-(aq) to leave the following:
Mg^2+(aq) + CO3^2-(aq) ==> MgCO3(s)
The ions you canceled are called spectator ions.

An example of a reaction that forms no ppt is b.
Obviously you need to know which salts are soluble. Here is a simplified table of solubility rules.

http://www.files.chem.vt.edu/RVGS/ACT/notes/solubility_rules.html

Answer 2

2mg(s)+o2(g)=2mgo(s)