Writing Formula, Complete and Net Ionic Equations Objective: write a molecular/formula equation, complete ionic equation, and net ionic equation that represent a reaction

Writing Formula, Complete and Net Ionic Equations We must be able to represent a reaction in three different ways: Molecular/Formula Equation Complete Ionic Equation Net Ionic Equation

What really happens when you put AgNO3 (aq) + NaCl(aq) AgCl(s) + NaNO3(aq) What really happens when you put AgNO3 and NaCl in water?

AgNO3 NaCl

NO3- Na+ Ag+ Cl-

Na+ NO3- Cl- Ag+

Na+ NO3- AgCl

Na+ NO3- AgCl(s) precipitate AgCl

AgCl(s) NO3- Na+ NO3- NO3- Na+ Na+ Na+ NO3- NO3- Na+ Na+ Na+ NO3- NO3-

NaNO3 (aq) Na +1 (aq) + (NO3) -1 (aq) really means: “dissociated ions” or “ions in solution”

AgCl (s) really means: Solid Silver (I) Chloride. How do we know this is insoluble? SOLUBILITY RULES (see handout)

Molecular / Formula Equation: A chemical equation in which all the reactants and products are given by their chemical formula. For Example: AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) Soluble species are indicated by placing “(aq)” after the formula. Precipitates are indicated by placing “(s)” after the formula. This way of expressing the reaction is used whenever we want to indicate the chemical formula of the reactants and products.

Complete Ionic Equation Shows all the soluble ionic species broken up into their respective ions. For Example: Ag+(aq)+ NO3-(aq)+ Na+(aq)+ Cl-(aq) → AgCl(s)+ Na+(aq)+ NO3-(aq) Spectator ions: Ions that remain unchanged during a reaction and do not participate in the reaction. The spectator ions in the above equation are NO3-(aq) and Na+(aq) NEVER write a complete ionic equation until you have first written a molecular formula equation. If you proceed directly to a complete ionic equation, the result may not represent the actual situation.

Net Ionic Equation: Shows only the reacting species (species which are actively involved in the reaction…the one making the PPT) in the equation. The net ionic equation is formed by omitting the spectator ions from the complete ionic equation and then balancing the reaction. For Example: We had: AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) then: Ag+(aq)+ NO3-(aq)+ Na+(aq)+ Cl-(aq) → AgCl(s)+ Na+(aq)+ NO3-(aq) Canceling out spectator ions, we get: Ag+(aq)+ Cl-(aq) → AgCl(s)

Na3PO4 + KNO3 → NaNO3 + K3PO4 What really happens when you put Na3PO4 and KNO3 in water (assume aqueous)?

Look at solubility rules (see handout) Na3PO4 KNO3

Look at solubility rules (see handout) NO3- Na+ K+ PO4-3 Na+ Na+

Look at solubility rules (see handout) NO3- Na+ NO3- K+ Na+ Na+ PO4-3 NO3- Na+ PO4-3 Na+ Na+ PO4-3 K+ K+ Na+ Na+ PO4-3 Na+

K3PO4 (aq) K +1 (aq) + (PO4) -3 (aq) really means: “dissociated ions” or “ions in solution” How do we know this is soluble? SOLUBILITY RULES (see handout)

NaNO3 (s) Na +1 (aq) + (NO3) -1 (aq) really means: “dissociated ions” or “ions in solution” How do we know this is soluble? SOLUBILITY RULES (see handout)

Na1+ (aq) + NO31-(aq) + K1+ (aq)+ PO43-(aq) 1. Write the molecular formula equation. Determine if there is a precipitate using“(s)” to identify the precipitate. The molecular formula equation is: Na3PO4 + KNO3 → NaNO3 + K3PO4 . Write the complete ionic equation by breaking up the balanced molecular formula equation into ions. We get: Na1+ (aq)+ PO43-(aq)+K1+ (aq)+NO31-(aq)  Na1+ (aq) + NO31-(aq) + K1+ (aq)+ PO43-(aq) 3. Write the net ionic equation by deleting the spectator ions and simplifying the coefficients if necessary. NO REACTION OCCURS

Let’s try an example putting all these ideas together Write a molecular/formula equation, a complete ionic equation, and a balanced net ionic equation for the reaction which occurs when 0.2 M solutions of Al(NO3)3(aq) and MgS(aq) are mixed.

Al(NO3)3(aq) + MgS(aq) → Al2S3(s) + Mg(NO3)2(aq) 1. Write the complete formula equation. Determine if there is a precipitate using“(s)” to identify the precipitate. The molecular formula equation is: Al(NO3)3(aq) + MgS(aq) → Al2S3(s) + Mg(NO3)2(aq) 2. Write the complete ionic equation by breaking up the molecular formula equation into ions. Remember: The precipitate remains in molecular form. We get: Al3+(aq) + NO3-(aq) + Mg2+(aq) + S2-(aq)  Al2S3(s) + Mg2+(aq) + NO3-(aq) 3. Write the balanced net ionic equation by deleting the spectator ions and balancing the reaction. Al3+(aq) + S2-(aq) → Al2S3(s) 2 Al3+(aq) + 3 S2-(aq) → Al2S3(s)

Let’s Try Some More Write the formula, complete ionic, and net ionic equation for each of the following reactions: Nickel (II) chloride reacts with sodium hydroxide Solid potassium metal reacts with water. HNO3(aq) + KOH(aq)  1. Equation: NiCl2(aq) + 2NaOH(aq) ---> Ni(OH)2(s) + 2NaCl(aq) Ionic: Ni2+(aq) + 2Cl-(aq) + 2Na+(aq) + 2OH-(aq) ---> Ni(OH)2(s) + 2Na+(aq) + 2Cl-(aq) Net ionic: Ni2+(aq) + 2OH-(aq) ---> Ni(OH)2(s) Formula Equation: 2 K (s) + 2 H2O (l) → 2 KOH (aq) + H2 (g) Ionic Equation: 2 K (s) + 2 H2O (l) → 2 K+ (aq) + 2 OH- (aq) + H2 (g) 3. H+ (aq) + NO3¯(aq) + K+ (aq) + OH¯(aq) K+ (aq) + NO3¯(aq) + H2O(l) Ionic Equation H+ (aq) + NO3¯(aq) + K+ (aq) + OH¯(aq) K+ (aq) + NO3¯(aq) + H2O(l) net ionic equation: H+ (aq) + OH¯(aq) H2O(l)