Net Ionic Equations

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Net Ionic Equations
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What are they?

• Net ionic equations are equations that show only
  the soluble, strong electrolytes reacting (these
  are represented as ions) and omit the spectator
  ions, which go through the reaction unchanged.
• They are the bare bones of the chemical reaction.

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Where do they take place?

• They usually take place in aqueous (aq)
  environments.
• To write them you need to understand solubility
  rules. (These are summarized on your activity
  series chart).

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Solubility Rule Highlights

• Most alkali metal compounds and NH4 compounds
  are soluble.
• Cl-, Br-, I- compounds are soluble, except when
  they contain Ag, Hg22, or Pb2.
• F- compounds are soluble, except when they
  contain group 2A metals.
• NO3-,ClO3- , ClO4- and CH3COO- compounds are
  soluble.
• SO42- compounds are soluble, except when they
  include Ca2, Sr 2, Ba 2, Ag , Pb 2, or
  Hg22.
• CO32-, PO43-,C2O42-, CrO42-, S2-, OH-, and O2-
  compounds are insoluble.
• All nitrates (NO3-) are soluble.

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How do we write them?

• Write a balanced equation for the reaction
  showing all states!
• Rewrite the equation, breaking apart soluble
  compounds (reactants and products) intoions
  where appropriate.
• Cancel all spectator ions and rewrite the
  remaining net ionic equation.

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Some Other Guidelines

• All ionic substances in aqueous form in the
  nonionic equation are written as separate ions.
• All acids in aqueous form in the nonionic
  equation are written as separate ions
• All solids, liquids and gases are written
  unchanged.

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Example (Single Replacement)

• Complete Molecular Equation
• Zn (s) 2 HCl (aq) ? ZnCl2 (aq) H2 (g)
• Now we need to evaluate the products and
  reactants and write a complete ionic reaction

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Think it through

• Zinc is a solid so is left alone Zn (s).
• HCl is an acid in aqueous form so is written as
  separate ion 2 H (aq) and 2 Cl - (aq) .
• ZnCl2 (aq) is an ionic substance so is written
  as separate ions Zn 2 (aq) and 2 Cl- (aq).
• Hydrogen is a gas and is therefore left alone
  H2 (g).

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Write Complete Ionic Equation

• Zn (s) 2H(aq) 2Cl -(aq) ? Zn 2(aq)
  2Cl-(aq) H2(g)

Now we need to evaluate the products and
reactants, find and eliminate any spectator ions,
and write a net ionic reaction
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Identify Spectator Ions

• Zn (s) 2H(aq) 2Cl -(aq) ? Zn 2(aq)
  2Cl-(aq) H2(g)

A spectator ion DOES NOT CHANGE during the
reaction. If it is the same on both sides of the
reaction, it did not participate!
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Write Net Ionic Equation

• Zn (s) 2H(aq) ? Zn 2(aq) H2(g)

The net ionic equation only shows the reactants
and products that actually participated in the
reaction.
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Same for Double Replacement!

• Complete Molecular Equation
• NaCl (aq) AgNO3 (aq) ---gt AgCl(s) NaNO3 (aq)

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Solubility Rules Revisited

• Notice that AgCl (s) is an INSOLUBLE salt.
• Thats why learning and using the solubility
  rules is so important!

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Same for Double Replacement!

• Write Complete Ionic Equation
• Na(aq) Cl- (aq) Ag(aq) NO3-(aq) ? AgCl(s)
  Na(aq) NO3-(aq)

Identify Spectator Ions Na(aq) Cl- (aq)
Ag(aq) NO3-(aq) ? AgCl(s) Na(aq) NO3-(aq)
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Same for Double Replacement!

• Write Net Ionic Equation
• Ag(aq) Cl-(aq) ? AgCl(s)
• Notice that since AgCl(s)
• is an INSOLUBLE solidyou cannot break it into
  ions!