Explanation:
Step 1: Write the balanced "molecular" equation:
[tex]2HI(aq) + NIS (s) → NiI₂(aq) + H₂S(g)[/tex]
Step 2: H₂S is written in molecular form. Consult the solubility and net ionic equation rules on the information page to determine which of the other substances will dissociate:
[tex]2HI(aq) + NIS (s) → NiI₂(aq) + H₂S(g)[/tex]
yes no yes
Step 3: Dissociate all soluble salts, strong acids, and strong bases (except calcium hydroxide). Leave together all "not soluble" salts and weak acids or bases:
[tex] {2H₃O}^{ + } (aq) + {2I}^{ - } (aq) + NiS(s)→ { Ni}^{2 + }(aq) + {2I}^{ - }(aq) + H₂S(g) + 2H₂O(l)[/tex]
Step 4: Cross out "spectator ions" that appear on both sides of the reaction (these ions do not participate in the chemistry) and rewrite the "net" reaction using the smallest possible coefficients:
[tex] {2H₃O}^{ + } (aq) + NiS(s) → { Ni}^{2 + } (aq) + H₂S(g) + 2H₂O(l)[/tex]
