Representing Aqueous Ionic Reactions With Net Ionic Reactions

NaCl is soluble in water Solid NaCl dissociates into Na + and Cl - ions in aqueous solution: What actually happens in Water NaCl (s)  Na + (aq) + Cl - (aq)

Total & Net Ionic Equations For reactions to happen, there are ions present in the solution that participate in the reaction There are other ions in the solutions are not important and do not affect the net result These are called SPECTATOR IONS

Mixing a solution that contains silver ions with a solution that contains chloride ions produces a white precipitate of silver chloride. There are other ions present in each solution, you know this because you cannot have a solution of just ions. Lets say the silver was silver I nitrate and the chloride was sodium chloride. It does not matter what the other ions are for the net result. AgNO 3 (aq) + NaCl (aq)  AgCl (s) + NaNO 3 (aq)

Ions that are not involved in the precipitate production, are passive onlookers. These are called spectator ions. AgNO 3 (aq) + NaCl (aq)  AgCl (s) + NaNO 3 (aq) This equation shows the reactants and products as intact compounds. In reality, soluble ionic compounds (like sodium nitrate) dissolve into their respective ions in an aqueous solution. Ag + + NO Na + + Cl -  AgCl (s) + Na + + NO 3 - The AgCl is still written as its ionic formula because it is insoluble.

Ag + + NO Na + + Cl -  AgCl (s) + Na + + NO 3 - Also notice that some ions appear on both sides of the equation. These ions can be eliminated from the NET IONIC EQUATION. Ag + + NO Na + + Cl -  AgCl (s) + Na + + NO 3 - The Net ionic equation is: » Ag + + Cl -  AgCl (s)

Net Ionic Equations A net ionic equation is written without spectator ions. There are some guidelines to follow when writing net ionic equations.

Pb(NO 3 ) 2 + 2NaI  PbI 2 + 2NaNO 3 (aq) (aq) (s) (aq) This equation shows all reactants and products intact as compounds. However, soluble ionic compounds dissociate into their respective ions in solution.

Net Ionic Equations Balanced Chemical Equation: Pb(NO 3 ) 2 (aq) + 2NaI (aq)  PbI 2 (s) + 2NaNO 3 (aq) “ Complete Ionic ” Equation: Pb 2+ (aq) + 2NO 3 - (aq) + 2Na + (aq) + 2I - (aq)  PbI 2 (s) + 2Na + (aq) + 2NO 3 - (aq) Cancel the “ spectator ions ” that appear on both sides of the arrow Pb 2+ (aq) + 2NO 3 - (aq) + 2Na + (aq) + 2I - (aq)  PbI 2 (s) + 2Na + (aq) + 2NO 3 - (aq) “ Net Ionic ” Equation: Pb 2+ (aq) + 2I - (aq)  PbI 2 (s)

Guidelines for Writing Net Ionic Equations 1.Include only ions and compounds that have reacted. Do not include spectator ions. 2.Write the soluble ionic compounds as ions (NH 4 Cl should be written as NH 4 + and Cl - ). 3.Write insoluble ionic compounds as formulas, not ions (Zinc sulfide is insoluble and should be written as ZnS not Zn 2+ + S 2- ). 4.Covalent molecules do not produce ions in aqueous solutions so they are written in their molecular formulas.

5. Strong acids (which you will learn about more later) should be written in ion form. There are six strong acids and you NEED to know them. All other acids are weak acids and should be written in molecular form.  Hydrochloric acid - H + and Cl - not HCl  Hydrobromic acid- H + and Br - not HBr  Hydroiodic acid- H + and I - not HI  Sulfuric acid – H + and SO 4 2-  Nitric acid - H + and NO 3 -  Percholric acid - H + and ClO 4 -

6. Check that the net ionic equation is balanced for charges as well as for atoms.

Writing Net Ionic Equation Example A chemical reaction occurs when the following aqueous solutions are mixed: sodium sulfide and iron II sulfate. Identify the spectator ions and then write the balance net ionic equation. Write the formulas Write and balance equation Determine which one is insoluble Write ionic equation and eliminate spectator ions Write net ionic equation

Na + + S 2-  Na 2 S Fe 2+ + SO 4 2-  FeSO 4 Na 2 S (aq) + FeSO 4 (aq)  Na 2 SO 4(aq) + FeS (s) solubleinsoluble 2Na + + S 2- + Fe 2+ + SO 4 2-  2Na + + SO FeS Fe 2+ + S 2-  FeS

Ba(NO 3 ) 2 + NiSO 4 Balanced Molecular Equation:

Ba(NO 3 ) 2 + NiSO 4 Ni(NO 3 ) 2 + BaSO 4 Balanced Molecular Equation:

Ba(NO 3 ) 2(aq) + NiSO 4(aq) Ni(NO 3 ) 2 (aq) + BaSO 4(s) Balanced Molecular Equation:

Ba 2+ (aq) + 2NO 3 - (aq) + Ni 2+ (aq) + SO 4 2- (aq) Ni 2+ (aq) + 2NO 3 - (aq) + BaSO 4 (s) Balanced Molecular Equation: Complete Ionic Equation: Ba(NO 3 ) 2(aq) + NiSO 4(aq) Ni(NO 3 ) 2 (aq) + BaSO 4(s)

Ba 2+ (aq) + 2NO 3 - (aq) + Ni 2+ (aq) + SO 4 2- (aq) Ni 2+ (aq) + 2NO 3 - (aq) + BaSO 4 (s) Balanced Molecular Equation: Complete Ionic Equation: Ba(NO 3 ) 2(aq) + NiSO 4(aq) Ni(NO 3 ) 2 (aq) + BaSO 4(s)

Ba 2+ (aq) + 2NO 3 - (aq) + Ni 2+ (aq) + SO 4 2- (aq) Ni 2+ (aq) + 2NO 3 - (aq) + BaSO 4 (s) Balanced Molecular Equation: Complete Ionic Equation: Ba(NO 3 ) 2(aq) + NiSO 4(aq) Ni(NO 3 ) 2 (aq) + BaSO 4(s) Net Ionic Equation: Ba 2+ (aq) + SO 4 2- (aq) BaSO 4 (s)