Unit 4: Chemical Equations and Stoichiometry

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Unit 4 Chemical Equations and Stoichiometry

• Net Ionic Equations

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Net Ionic Equations

• For reactions taking place in water many
  substances dissociate (break apart) into ions
• To write a net ionic equation you must determine
  which compounds dissociate and which do not

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Net Ionic Rules

• Which molecules dissociate (break apart)???
• Rule 1 Solids, liquids, and gases
• Do NOT dissociate
• Rule 2 Acids
• Strong acids dissociate HCl, HBr, HI, H2SO4,
  HNO3, HClO4
• Weak acids stay together
• Rule 3 Bases
• Strong bases dissociate Group 1 and 2
  hydroxides LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2,
  Sr(OH)2, Ba(OH)2 except Be(OH)2
• Weak bases stay together

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Net Ionic Rules

• Which molecules dissociate (break apart)???
• Rule 4 Ionic Compounds
• If soluble dissociate
• If insoluble stay together
• Use the table on p. 125 in your textbook or the
  chart on your periodic table

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Net Ionic Practice

• Determine whether the following compounds
  dissociate in water or not
• H2SO4
• FeS
• KOH
• Ca(NO3)2
• Cu3(PO4)2

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Net Ionic Equations

• For reactions taking place in water many
  substances dissociate (break apart) into ions
• To write a net ionic equation you must determine
  which compounds dissociate and which do not
• Spectator ions ions that do not actually
  participate in the reaction

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Steps to Writing Net Ionic Equations
Example Hydrochloric acid solution and sodium
hydroxide solution yield water and dissolved
sodium chloride
Step 1 Write and balance the molecular form
HCl (aq) NaOH (aq) ? H2O (l) NaCl
(aq)
Step 2 Determine which molecules dissociate and
rewrite in ionic formH(aq) Cl-(aq) Na(aq)
OH-(aq) ? H2O(l) Cl-(aq) Na(aq)
Spectator ions
Step 3 Cancel ions that appear on both sides
and rewrite what is left H (aq) OH- (aq) ?
H2O (l)
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Net Ionic Example 1

• Nickel nitrate sodium hydroxide ? nickel
  hydroxide sodium nitrate

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Net Ionic Example 2 on the WS

• Nickel nitrate sodium hydroxide ? nickel
  hydroxide sodium nitrate

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Net Ionic Decision Making Tree