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Formula, Total & Net Ionic Equations

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Step 1: If no products are given, then determine the products. Switch last names

Step 2: Balance the equation.

 

Given: lead (II) nitrate  +  Sodium Chloride à   (Lead (II) Chloride and Sodium Nitrate)

                1)  Pb(NO3)2 (aq)  +  NaCl (aq)  à   PbCl2   +  NaNO3

                2)  Pb(NO3)2(aq)   +  2 NaCl(aq)  à   PbCl2  +  2 NaNO3

 

TOTAL IONIC EQUATION

As the name states, this equation shows ions (charges) for everything that is soluble or ionizes/dissociates 100%.

Step 3: Look at each compound in the formula unit and ask yourself: Is it soluble (aq)?

-If yes to any of the three questions, assign charges to each ION in the compound (compounds will usually contain a positive and negative ion)

      -If no, then leave the compound as it is

                         Pb(NO3)2(aq)   +  2 NaCl(aq)  à   PbCl2 (s) +  2 NaNO3 (aq)

                3) Pb2+(aq)    + 2NO3- (aq)   +  2 Na+(aq)  + 2Cl- (aq)  à   PbCl2(s)  +  2 Na+(aq)+ 2NO3- (aq) 

                                                               

        Question: Where did the coefficient 2 come from in front of Na+1 and Cl-1?

- Coefficient is the number we use to balance equations in the Formula Unit Equation. In the Total Ionic Equation, the coefficients come from

1) the coefficients in the formula unit equation and

2) from the subscript assigned when creating a compound. If you have both a coefficient and a subscript to account for on the same compound, you would multiply the two together:

 formula unit equation 2 CaBr2 à total ionic equation 2 Ca2+  +  4 Br-

  Spectator ions do not change their charge (remember ions are charged particles, not compounds). Whatever the charge was on the reactant side it will be the same charge on the product side of the equation. Spectators are present in the solution, but do not participate in the reaction. That is why they have no change in charge. Think of it like a sports fan: if you are a spectator, you are involved in the overall event because you are physically present and viewing the sport, but you do not participate in the action of the sport.

  NET IONIC EQUATION

Step 4: Look at each ion (not compound) in the Total Ionic Equation. Cancel out the identical spectator ions that are on both the reactant and product side. 

Step 5: What remains (doesn’t cancel) constitutes the Net Ionic Equation. You will always have something that doesn’t cancel. If everything cancels, go back and check your work, something is wrong.

**** Net ionic equations for ALL reactions of strong acids with strong soluble bases that form soluble salts and water is: H+  + OH-  à  H2O (l)

In other words, if you can’t find anything else, your net ionic equation will be: H+  + OH-  à  H2O (l)

                  4) Pb2+(aq)    + 2NO3- (aq)   +  2 Na+(aq)  + 2Cl- (aq)  à   PbCl2(s)  +  2 Na+(aq)+ 2NO3- (aq) 

                5) Pb2+(aq)  + 2Cl- (aq)  à   PbCl2(s) 

PRACTICE PROBLEMS-Highlight to reveal answers

 Write balanced formula unit, total ionic and net ionic equations for the following reactions. Assume all reactions occur in water or in contact with water.    

1. Silver nitrate and Rubidium chloride

Overall Equation:
AgNO3 (aq) + RbCl(aq) --> AgCl(s) + RbNO3 (aq)
Total Ionic Equation:
Ag+ (aq) + NO3- (aq) + Rb+(aq) + Cl-(aq) -> AgCl(s) + Rb+(aq) + NO3- (aq)
Net Ionic Equation:
Ag+ (aq) + Cl-(aq) -> AgCl(s)
 

2. mercury (I) nitrate and hydrochloric acid

Overall Equation:
Hg2(NO3)2 (aq) + 2 HCl (aq) --> Hg2Cl2 (s) + 2 HNO3 (aq)
Total Ionic Equation:
Hg22+(aq) + 2 NO3- (aq) + 2 H+(aq) + 2 Cl- (aq) --> Hg2Cl2 (s) + 2 H+ (aq) + 2 NO3-(aq)
Net Ionic Equation:
Hg2+(aq) + 2 Cl- (aq) --> Hg2Cl2 (s)
 

3. calcium chloride and sodium carbonate

Overall Equation:
CaCl2 (aq) + Na2CO3 (aq) -> 2 NaCl(aq) + CaCO3 (s)
Total Ionic Equation:
Ca2+(aq)+ 2 Cl- (aq) + 2 Na+ (aq)+ CO32- (aq) -> 2 Na+(aq) + 2 Cl-(aq) + CaCO3 (s)
Net Ionic Equation:
Ca2+(aq) + CO32- (aq) -> CaCO3 (s)

 
4. magnesium nitrate and calcium chloride

Overall Equation:
Mg(NO3)2 (aq) + CaCl2 (aq) -> Ca(NO3)2 (aq) + MgCl2 (aq)
Total Ionic Equation:
Mg2+ (aq) + 2 NO3- (aq) + Ca2+ (aq) + 2 Cl- (aq) --> Ca 2+(aq) + 2 NO3- (aq) + Mg2+(aq) + 2 Cl- (aq)
Net Ionic Equation:
No Reaction

 
5. potassium sulfate and barium chloride

Overall Equation:
K2SO4 (aq) + BaCl2 (aq) --> BaSO4 (s) + 2 KCl (aq)
Total Ionic Equation:
2 K+ (aq)+ SO42- (aq) + Ba2+ (aq) + 2 Cl- (aq) --> BaSO4 (s) + 2 K+(aq)+ 2 Cl- (aq)
Net Ionic Equation:
SO42- (aq) + Ba2+ (aq) -> BaSO4 (s)

More problems- AP Chemistry

1) acetic acid + sodium hydroxide à

 

ANSWER

1)     Formula Unit:       HC2H3O2  +  NaOH  à  NaC2H3O2  + H2O
 Total Ionic:        HC2H3O2     + Na+1  + OH-1  à  Na+1  +  C2H3O2-1  + H2O

Weak acid
Net Ionic:         HC2H3O2    + OH-1  à   C2H3O2-1  + H2O

2) calcium hydroxide + hydrosulfuric acid à

 ANSWER

2)     Formula Unit:      Ca(OH)2  +  H2S  à  CaS  +  2 H2O
 Total Ionic:        Ca+2  +  2OH-1  +  2H +1  +  S-2  à    Ca+2  +  S-2  +  2 H2O
Net Ionic:          2OH-1  +  2H +1  à    2 H2O

 OH-1  +  H +1  à    H2O

   3) Ba(NO3)2  +  K2CO3 à

 ANSWER

3)     Formula Unit:      Ba(NO3)2  + K2CO3  à  BaCO3  +  2KNO3
 Total Ionic:        Ba+2  +  2NO3-1   +  2K +1  +  CO3-2  à  BaCO3  Insoluble   +  2K+1 +  2NO3-1
Net Ionic:         Ba+2  +  CO3-2  à  BaCO3   Insoluble   

  4) lead (II) hydroxide  + carbonic acid  à

 ANSWER

4)     Formula Unit:      Pb(OH)2  + H2CO3  à  PbCO3  +  2H2O
 Total Ionic:        Pb(OH)2  +        H2CO3   à         PbCO3  +     2H2O

 Insoluble       Weak Acid            Insoluble    liquid                                                                
Net Ionic:         Pb(OH)2  + H2CO3  à  PbCO3  +  2H2O

5) Our bones are mostly calcium phosphate. Calcium chloride reacts with potassium phosphate to form calcium phosphate and potassium chloride.

 ANSWER

5)     Formula Unit:      3CaCl2  +  2K3PO4  à  Ca3(PO4)2  + 6KCl
 Total Ionic:        3Ca+2  +  6Cl-1  +  6K+1   +  2 PO4-3  à  Ca3(PO4)2     Insoluble         +   6K+1  + 6Cl-1
Net Ionic:         3Ca+2  +   2 PO4-3  à  Ca3(PO4)2   Insoluble         

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