Question

Write a net ionic equation for the reaction that occurs when excess hydroiodic acid and chromium(II) carbonate (s) are combined.

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Answer 1

Step 1: Write the balanced "molecular equation:

`2HI(aq) + CrCO₃ (s) → CrI₂ (s) + H₂O(l) + CO₂(g)`

Step 2: Carbon dioxide and water are 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:

`2HI(aq) + CrCo₃ (s) → Crl₂ (s) +H₂O(l)+CO₂(g)`

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:

`{2H₂O}^( + ) (aq) + {2I}^( - ) (aq) + CrCO₃ (s)→ {Cr}^(2 + ) (aq) + {2I}^( - )(aq) + 3H₂O(l) + CO₂(g)`

Step 4: Cross out "spectator lons that appear on both sides of the reaction (these lons do not participate in the chemistry) and rewrite the "net" reaction using the smallest possible coefficients:

`{2H₂O}^( + ) (aq) + CrCO₃ (s) →3H₂O + CO₂ + {Cr}^(2 + )`