Net Ionic Equations

Driving Forces of Ionic Rxns (Double Replacement) Ionic rxns usually occur between 2 aqueous solutions, each containing a dissolved compound in an aqueous ionic state. – Possible results of mixing two solutions: 1. One of the possible products is INSOLUBLE in water & settles out from solution as a solid precipitate. – Consult solubility table – Ex. Sodium sulfate (aq) + Lead (II) nitrate (aq)  lead (II) sulfate + sodium nitrate INSOLUBLE!(aq) Na 2 SO 4 (aq) + Pb(NO 3 ) 3 (aq)  PbSO 4  + 2 NaNO 3 (aq)

Driving Forces of Ionic Rxns 2. An acid (H + producing compound) reacts with a base (OH - producing compound). One of the products of the reaction is HOH ( l ), an essentially unionized product. – Acid-Base neutralization reaction. – Ex. Sulfuric acid (aq) + Sodium hydroxide (aq)  sodium sulfate + HOH (aq) (l) H 2 SO 4 (aq) + 2 NaOH (aq)  Na 2 SO 4 (aq) + 2 HOH ( l )

Driving Forces of Ionic Rxns 3. One of the possible products is an unstable compound which breaks down to form a gaseous product and water. – Watch for the ions: » Carbonate, Sulfite, Ammonium – Ex. Hydrochloric acid (aq) + Sodium carbonate (aq)  sodium chloride + hydrogen carbonate (carbonic acid) Would both be aqueous, but there is an unstable product. 2 HCl (aq) + Na 2 CO 3 (aq)  2 NaCl (aq) + H 2 CO 3 (aq) H 2 O (l) + CO 2  2 HCl (aq) + Na 2 CO 3 (aq)  2 NaCl (aq) + H 2 O (l) + CO 2  H 2 CO 3 H 2 SO 3 NH 4 OH

Net Ionic Equations (NIE) Are typically derived from single replacement or ionic/double-replacement reactions. – Shows ONLY the substances/ions that are involved in the chemical change that occurs in the reaction. A reaction’s NIE can be the same as its molecular equation. See handout for steps to determining NIE.

Net Ionic Equations (NIE) Steps in writing net ionic equations: – 1. Write and balance the complete molecular equation. (INCLUDING all phases of matter) – 2. Show any compounds in aqueous solution (aq) as dissociated ions. Ex. HNO 3(aq)  Ex. H 2 SO 4(aq)  – 3. Cancel out (remove from eq.) any Spectator Ions. These are (aq) ions that appear on both sides of the rxn, and so are NOT changed BY the rxn. – 4. Whatever is left IS the NIE. If nothing cancels then the equation is already the molecular AND the NIE. H + (aq) + NO 3 1- (aq) 2 H + (aq) + SO 4 2- (aq)

NIE Examples Example #1: – Sodium bromide (aq) + Lead (II) nitrate (aq)  Write the equation : – NaBr (aq) + Pb(NO 3 ) 2(aq)  NaNO 3(aq) + PbBr 2  Balance the equation: – 2 NaBr (aq) + Pb(NO 3 ) 2(aq)  2 NaNO 3(aq) + PbBr 2  Expand the equation to show aqueous ions: (this is the Complete Ionic Equation) – 2 Na + (aq) + 2 Br 1– (aq) + Pb 2+ (aq) + 2 NO 3 1– (aq)  2 Na + (aq) + 2 NO 3 1– (aq) + PbBr 2  2 Br 1– (aq) + Pb 2+ (aq)  PbBr 2  2 Br 1– (aq) + Pb 2+ (aq)  PbBr 2  This is the NET IONIC EQUATION (NIE). Eliminate Spectator Ions: Eliminate Spectator Ions:

NIE Examples Example #2: – Zinc (s) + Hydrochloric acid (aq)  Write and Balance the equation : – Zn (s) + 2 HCl (aq)  ZnCl 2(aq) + H 2(g) Expand the equation and cancel spectator ions: – Zn (s) + 2 H + (aq) + 2 Cl 1- (aq)  Zn 2+ (aq) + 2 Cl 1- (aq) + H 2  Write the NIE : Write the NIE : Zn (s) + 2 H + (aq)  Zn 2+ (aq) + H 2(g) Zn (s) + 2 H + (aq)  Zn 2+ (aq) + H 2(g)

YOU TRY: NIE Problem Ammonium Chloride (aq) + Sodium hydroxide  NIE: NH 4 +1 (aq) + OH 1– (aq)  NH 3  + H 2 O ( l ) NH 4 +1 (aq) + OH 1– (aq)  NH 3  + H 2 O ( l )