1. Ppt15, Net Ionic Equations (mainly) PS6 material, continued
Reminder, Electrolytes
Reminder, Ionic Compounds
Reminder, Stoichiometry of Electrolytes
Net Ionic Equations
→ Expressing what really happens
Exchange Reactions (Double Displacement
Reactions)
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2. Ppt15

3. NaCl (aq)  Na+ (aq) + Cl- (aq)
Ionic Compounds
dissociate into constituent ions when dissolved
hence, they are strong electrolytes if they are soluble
“Strong” = ions dissociate stoichiometrically (~100% of FU’s separate)
NaCl (aq)  Na+ (aq) + Cl- (aq)
K2S (aq)  2 K+ (aq) + S2- (aq)
(NH4)2CO3 (aq)  2 NH4+ (aq) + CO32- (aq)
CaCO3 (s)  not soluble
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4. 4

5. Review
How many moles of K+ ions are present in 0.25 L of M K2CO3 solution?
K2CO3  2 K+(aq) CO32-(aq) L x mol x 2 mol K+ = L mol K2CO mol K+
subscript (ratio)
[mol A from mol AxBy]
mol K2CO3 [M x V = mol]
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6. Acids/Bases/Salts Acids
have an ionizable hydrogen, H+ eg. HCl(aq) or HC2H3O2(aq)
can be strong or weak electrolytes
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7. Strong Acids--know these!
HCl, HBr, HI, HNO3, H2SO4, HClO4
Any other acid is therefore WEAK!!
Bases
substances that react with acids
produce hydroxide ions, OH-, in solution
can be strong electrolytes (soluble ionic hydroxides) or weak electrolytes (NH3 or similar molecular compounds)
NaOH(aq)  Na+(aq) OH-(aq)
NH3(aq) + H2O  NH4+(aq) OH-(aq)
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9. Molecular vs. Ionic Equations
Three ways to express chemical equations
molecular equation--all species expressed as neutral formulas (regardless of whether substance is molecular or not)
HCl(aq) NaOH(aq)  H2O(l) NaCl(aq)
(HCl(aq) is really H+(aq) and Cl-(aq) in solution)
complete ionic equation--all STRONG ELECTROLYTES are expressed in ionic form H+(aq)+ Cl-(aq) + Na+(aq) + OH-(aq)  H2O(l) + Na+(aq) + Cl-(aq)
spectator ions: ions that undergo no change
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10. NET ionic equation--incl
NET ionic equation--incl. only species that change (so cross out any that are on both sides [spectators])
H+(aq) OH-(aq) ® H2O(l)
Remember, only strong electrolytes (i.e., soluble ionic compounds OR strong acids) are written in ionic form!
Examples
H2S(aq) + 2NaOH(aq) ® 2H2O(l) + Na2S(aq) (molec. eqn)
H2S(aq) + 2Na+(aq) + 2OH-(aq) ® 2H2O(l) + 2Na+(aq) + S2-(aq)
H2S(aq) + 2OH-(aq) ® 2H2O(l) + S2-(aq) (net ionic eqn)
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11. Exchange* Reactions (*Double Displacement)
General Form
ion partner exchange
_AmXn _BpYq  _ArYs _BuXv
Pb(NO3) K2S 
Driving Forces
formation of an insoluble solid [see precipitate]
formation of a weak or non-electrolyte [warms]
formation of a gas [see bubbles]
PbS 2
KNO3
(aq)
(aq)
(s)
(aq)
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12. Precipitation Reaction
formation of an insoluble solid
know the solubility guidelines!!
examples:
NaCl(aq) KNO3(aq)  NaNO3(aq) KCl(aq)
AgNO3(aq) KCl(aq) 
???
Na+ + Cl- + K+ + NO ®
Na+ + NO K+ + Cl-
NOTHING CHANGED!  “no reaction”
(just a bunch of ions swimming around in solution!)
AgCl KNO3 aq
(soluble)
Solid (insoluble)
Ag+ + NO K+ + Cl- ®
AgCl(s) + K NO3-
Ag+(aq) + Cl-(aq) ® AgCl(s)
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13. Formation of a weak or non-electrolyte
common example is an acid/base reaction--H2O forms
know/recognize electrolyte vs non-electrolyte
examples: HCl(aq) NaOH(aq)  H2O(l) NaCl(aq)
NiO(s) HNO3(aq)  Ni(NO3)2(aq) H2O(l)
H+ + Cl- + Na+ + OH- ®
H2O + Cl- + Na+
H+ + OH- ® H2O
NiO(s) + 2H+ + 2NO3- ®
Ni NO H2O
NiO(s) + 2H+ ® Ni H2O
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14. Formation of a gas
gases exit the reacting solution driving the reaction
examples:
2HCl(aq) + Na2CO3(aq)  2NaCl(aq) + H2O(l) + CO2(g) HCl(aq) + Na2S(aq)  2NaCl(aq) H2S(g)
2H+ + 2Cl- + 2Na+ + CO32- ®
2Na+ + 2Cl- + H2CO3
H2O + CO2
2H+ + 2Cl- + 2Na+ + S2- ®
2Na+ + 2Cl- + H2S(g)
PS6 Written, problems 7-9 reflect this material
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