Chemistry Solution Reaction?

Question

What is the net ionic equation for the reaction between a sodium sulfide solution and a ferrous nitrate solution.

Tell me how you know it is aqueos or solid

Answer 1

We check for a precipitation reaction.  "Cross" the anions and cations (if you have compounds AB and CD, check if AD or CB are insoluble).  So here, we check the solubility of ferrous sulfide and sodium nitrate.  Sodium nitrate is soluble, but ferrous sulfide is not (memorize solubility rules to know this in the future - nearly all alkali metal compounds and nearly all nitrates are soluble, while almost all but alkali and alkali earth sulfides are insoluble.

So we would expect the reaction to be:

S2-(aq) + Fe2+(aq) -----> FeS(s)

This may be good enough for a basic chemistry course.  However, this answer is not technically correct.

S2- is too strong of a base to exist in aqueous solution; it will react as follows:

S2-(aq) + H2O(l) ------> HS-(aq) + OH-(aq)

So the "sodium sulfide solution" actually consists of Na+, HS-, and OH- ions.

Thus, the more correct equation is:

Fe2+(aq) + HS-(aq) + OH-(aq) ------> FeS(s) + H2O(l)