Going from Molecular Equations to Ionic Equations
To write an ionic equation, starting from the molecular equation, you need only identify the reactants and products which are both soluble (aq) and strong electrolytes. Refer to other review web pages for help with those topics.
For all of those components which are both soluble and strong electrolytes, you should write them out as their separate ions. Always include charges and physical states for the ions (they will all be aqueous).
One exception to the pattern for breaking the compounds into ions occurs for sulfuric acid. Since only the first hydrogen is ionized completely, in ionic equations, sufluric acid is written as hydrogen and bisulfate ions (instead of hydrogen and sulfate as might be expected).
For the net ionic equation, cancel out spectator ions, which are ions that appear exactly the same on both sides of the equation.
Note that metal elements do not have charges - they are not ions, and they are always solids (except mercury which is a liquid).
EXAMPLES: Write a total ionic and net ionic equation for each of the following aqueous reactions.
(1) BaCl2(aq) + CuSO4(aq) ---> BaSO4(s) + CuCl2(aq)
Answer:
| species | soluble? | strong electrolyte? | ions |
| BaCl2 | yes | salt - strong | Ba2+ and 2 Cl- |
| CuSO4 | yes | salt - strong | Cu2+ and SO42- |
| BaSO4 | no | N/A | N/A |
| CuCl2 | yes | salt - strong | Cu2+ and 2 Cl1- |
total ionic: Ba2+(aq) + 2 Cl1-(aq) + Cu2+(aq) + SO42-(aq) ---> BaSO4(s) + Cu2+(aq) + 2 Cl1-(aq)
net ionic: Ba2+(aq) + SO42-(aq) ---> BaSO4(s)
(2) H2SO4(aq) + Pb(NO3)2(aq) ---> 2 HNO3(aq) + PbSO4(s)
Answer:
| species | soluble? | strong electrolyte? | ions |
| H2SO4 | yes | acid - strong | H1+ and HSO41- |
| Pb(NO3)2 | yes | salt - strong | Pb2+ and 2 NO31- |
| HNO3 | yes | acid - strong | H1+ and NO31- |
| PbSO4 | no | N/A | N/A |
total ionic: H1+(aq) + HSO41-(aq) + Pb2+(aq) + 2 NO31-(aq) ---> 2 H1+(aq) + 2 NO31-(aq) + PbSO4(s)
net ionic: HSO4-(aq) + Pb2+(aq) ---> H+(aq) + PbSO4(s)
PRACTICE EXERCISES:
Write a total ionic and net ionic equation for each of the following aqueous reactions.
QUESTIONS:
| 1. | 2 Au(NO3)3(aq) + 3 Sr(OH)2(aq) --> 2 Au(OH)3(s) + 3 Sr(NO3)2(aq) |
| 2. | 2 AlI3(aq) + 3 Pb(C2H3O2)2(aq) --> 2 Al(C2H3O2)3(aq) + 3 PbI2(s) |
| 3. | Na2SO3(aq) + 2 HNO3(aq) --> 2 NaNO3(aq) + H2O(l) + SO2(g) |
| 4. | 2 HBr(aq) + BaS(aq) --> H2S(g) + BaBr2(aq) |
| 5. | LiCN(aq) + HCl(aq) --> LiCl(aq) + HCN(aq) |
| 6. | SrI2(aq) + H2SO4(aq) --> 2 HI(aq) + SrSO4(s) |
| 7. | Hg2(NO3)2(aq) + 2 NaBr(aq) --> Hg2Br2(s) + 2 NaNO3(aq) |
| 8. | Rb3PO4(aq) + CrCl3(aq) --> 3 RbCl(aq) + CrPO4(s) |
| 9. | Mg(s) + CuSO4(aq) --> MgSO4(aq) + Cu(s) |
| 10. | 2 Au(NO3)3(aq) + 3 Zn(s) --> 2 Au(s) + 3 Zn(NO3)2(aq) |
| 11. | 2 Al(s) + 3 Pb(C2H3O2)2(aq) --> 2 Al(C2H3O2)3(aq) + 3 Pb(s) |
| 12. | Mn(s) + 2 HNO3(aq) --> Mn(NO3)2(aq) + H2(g) |
| 13. | H2(g) + Pt(NO3)2(aq) --> 2 HNO3(aq) + Pt(s) |
| 14. | NiBr2(aq) + Co(s) --> Ni(s) + CoBr2(aq) |
| 15. | H3PO4(aq) + 3 KOH(aq) --> 3 H2O(l) + K3PO4(aq) |
1:00-2:00
ANSWERS (If you do not understand any of these, the go ask your instructor) :
| 1. | total: 2 Au3+(aq)
+ 6 NO31-(aq)
+ 3 Sr2+(aq)
+ 6 OH1-(aq)
---> 2 Au(OH)3(s)
+ 3 Sr2+(aq)
+ 6 NO31-(aq)
net: 2 Au3+(aq) + 6 OH1-(aq) ---> 2 Au(OH)3(s) |
| 2. | total: 2 Al3+(aq)
+ 6 I1-(aq)
+ 3 Pb2+(aq)
+ 6 C2H3O21-(aq)
---> 2 Al3+(aq)
+ 6 C2H3O21-(aq)
+ 3 PbI2(s)
net: 6 I1-(aq) + 3 Pb2+(aq) ---> 3 PbI2(s) simplify to: 2 I1-(aq) + Pb2+(aq) ---> 2 PbI2(s) |
| 3. | total: 2 Na1+(aq)
+ SO32-(aq)
+ 2 H1+(aq)
+ 2 NO31-(aq)
---> 2 Na1+(aq)
+ 2 NO31-(aq)
+ H2O(l)
+ SO2(g)
net: SO32-(aq) + 2 H1+(aq) ---> H2O(l) + SO2(g) |
| 4. | total: 2 H1+(aq)
+ 2 Br1-(aq)
+ Ba2+(aq)
+ S2-(aq)
---> H2S(g)
+ Ba2+(aq)
+ 2 Br1-(aq)
net: 2 H1+(aq) + S2-(aq) ---> H2S(g) |
| 5. | total: Li1+(aq)
+ CN1-(aq)
+ H1+(aq)
+ Cl1-(aq)
---> Li1+(aq)
+ Cl1-(aq)
+ HCN(aq)
net: CN1-(aq) + H1+(aq) ---> HCN(aq) NOTE: recall that HCN is a weak acid. |
| 6. | total: Sr2+(aq)
+ 2 I1-(aq)
+ H1+(aq)
+ HSO41-(aq)
---> 2 H1+(aq)
+ 2 I1-(aq)
+ SrSO4(s)
net: Sr2+(aq) + HSO41-(aq) ---> H1+(aq) + SrSO4(s) |
| 7. | total: Hg22+(aq)
+ 2 NO31-(aq)
+ 2 Na1+(aq)
+ 2 Br1-(aq)
---> Hg2Br2(s) + 2 Na1+(aq)
+ 2 NO31-(aq)
net: Hg22+(aq) + 2 Br1-(aq) ---> Hg2Br2(s) |
| 8. | total: 3 Rb1+(aq)
+ PO43-(aq)
+ Cr3+(aq)
+ 3 Cl1-(aq)
---> 3 Rb1+(aq)
+ 3 Cl1-(aq)
+ CrPO4(s)
net: PO43-(aq) + Cr3+(aq) ---> CrPO4(s) |
| 9. | total: Mg(s) + Cu2+(aq)
+ SO42-(aq)
--> Mg2+(aq)
+ SO42-(aq) + Cu(s)
net: Mg(s) + Cu2+(aq) --> Mg2+(aq) + Cu(s) |
| 10. | total: 2 Au3+(aq)
+ 6 NO31-(aq)
+ 3 Zn(s)
--> 2 Au(s) + 3 Zn2+(aq)
+ 6 NO31-(aq)
net: 2 Au3+(aq) + 3 Zn(s) --> 2 Au(s) + 3 Zn2+(aq) |
| 11. | total: Al(s) + 3 Pb2+(aq)
+ 6 C2H3O21-(aq)
--> 2 Al3+(aq)
+ 6 C2H3O21-(aq)
+ 3 Pb(s)
net: Al(s) + 3 Pb2+(aq) --> 2 Al3+(aq) + 3 Pb(s) |
| 12. | total: Mn(s) + 2 H1+(aq)
+ 2 NO31-(aq)
--> Mn2+(aq)
+ 2 NO31-(aq)
+ H2(g)
net: Mn(s) + 2 H1+(aq) --> Mn2+(aq) + H2(g) |
| 13. | total: H2(g) + Pt2+(aq)
+ 2 NO31-(aq)
--> 2 H1+(aq)
+ 2 NO31-(aq)
+ Pt(s)
net: H2(g) + Pt2+(aq) --> 2 H1+(aq) + Pt(s) |
| 14. | total: Ni2+(aq)
+ 2 Br1-(aq)
+ Co(s) -->
Ni(s)
+ Co2+(aq)
+ 2 Br1-(aq)
net: Ni2+(aq) + Co(s) --> Ni(s) + Co2+(aq) |
| 15. | total: H3PO4(aq)
+ 3 K1+(aq)
+ 3 OH1-(aq)
---> 3 H2O(l) + 3 K1+(aq)
+ PO43-(aq) net: H3PO4(aq) + 3 OH1-(aq) ---> 3 H2O(l) + PO43-(aq) NOTE: recall that H3PO4 is a weak acid. |
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