Net ionic equations and solubility rules

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Net ionic equations and solubility rules
S2
PO43
Na
2Ca2
3Cl
Al3
2
Review forming ions

• Ionic (i.e. salt) refers to ve ion plus -ve ion
• Usually this is a metal non-metal or metal
  polyatomic ion (e.g. NaCl, NaClO3, Li2CO3)
• Polyatomic ions are listed on page 71
• (aq) means aqueous (dissolved in water)
• For salts (aq) means the salt exists as ions
• NaCl(aq) is the same as Na(aq) Cl(aq)
• Acids form ions HCl(aq) is H(aq) Cl(aq),
• Bases form ions NaOH(aq) is Na OH
• Q - how is charge determined (1, -1, 2, etc.)?
• A - via valences (periodic table or see pg. 71)
• F, Cl gain one electron, thus forming F, Cl
• Ca loses two electrons, thus forming Ca2

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Background valences and formulas

• Charge can also be found via the compound
• E.g. in NaNO3(aq) if you know Na forms Na, then
  NO3 must be NO3 (NaNO3 is neutral)
• By knowing the valence of one element you can
  often determine the other valences
• Q - Write the ions that form from Al2(SO4)3(aq)?
• Step 1 - look at the formula Al2(SO4)3(aq)
• Step 2 - determine valences Al3 (SO4)2

• (Al is 3 according to the periodic table)
• Step 3 - write ions 2Al3(aq)
  3SO42(aq)
• Note that there are 2 aluminums because Al has a
  subscript of 2 in the original formula

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Practice with writing ions

• Q - Write ions for Na2CO3(aq)
• A - 2Na(aq) CO32(aq) (from the PT Na is 1.
  There are 2, thus we have 2Na. There is only
  one CO3. It must have a 2- charge)
• Notice that when ions form from molecules, charge
  can be separated, but the total charge (and
  number of each atom) stays constant.
• Q - Write ions for Ca3(PO4)2(aq) Cd(NO3)2(aq)
• A - 3Ca2(aq) 2PO43(aq)
• A - Cd2(aq) 2NO3(aq)
• Q - Write ions for Na2S(aq) and Mg3(BO3)2(aq)
• A - 2Na(aq) S2(aq), 3Mg2(aq) 2BO33(aq)

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Types of chemical equations

• Equations can be divided into 3 types (pg. 396)
• 1) Molecular, 2) Ionic, 3) Net ionic
• Here is a typical molecular equation
• Cd(NO3)2(aq) Na2S(aq) ? CdS(s) 2NaNO3(aq)
• We can write this as an ionic equation (all
  compounds that are (aq) are written as ions)
• Cd2(aq) 2NO3(aq) 2Na(aq) S2(aq)
  ?
  CdS(s) 2Na(aq) 2NO3(aq)
• To get the NET ionic equation we cancel out all
  terms that appear on both sides

Net Cd2(aq) S2(aq) ? CdS(s)
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Equations must be balanced

• There are two conditions for molecular, ionic,
  and net ionic equations
• Materials balance
• Both sides of an equation should have the same
  number of each type of atom
• Electrical balance
• Both sides of a reaction should have the same
  net charge
• Q- When NaOH(aq) and MgCl2(aq) are mixed,
  _______(s) and NaCl(aq) are produced. Write
  balanced molecular, ionic net ionic equations

Mg(OH)2
7

• First write the skeleton equation

NaOH(aq) MgCl2(aq)
? Mg(OH)2(s)
NaCl(aq) Next, balance the equation
2
2
Ionic equation 2Na(aq) 2OH-(aq) Mg2(aq)
2Cl-(aq)
? Mg(OH)2(s) 2Na(aq) 2Cl-(aq)
Net ionic equation 2OH-(aq) Mg2(aq) ?
Mg(OH)2(s) Write balanced ionic and net ionic
equations CuSO4(aq) BaCl2(aq) ? CuCl2(aq)
BaSO4(s) Fe(NO3)3(aq) LiOH(aq) ? ______(aq)
Fe(OH)3(s) Na3PO4(aq) CaCl2(aq) ? _________(s)
NaCl(aq) Na2S(aq) AgC2H3O2(aq) ? ________(aq)
Ag2S(s)
LiNO3
Ca3(PO4)2
NaC2H3O2
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Cu2(aq) SO42(aq) Ba2(aq) 2Cl(aq) ?
Cu2(aq) 2Cl(aq) BaSO4(s) Net SO42(aq)
Ba2(aq) ? BaSO4(s) Fe3(aq) 3NO3(aq)
3Li(aq) 3OH(aq) ? 3Li(aq) 3NO3(aq)
Fe(OH)3(s) Net Fe3(aq) 3OH(aq) ?
Fe(OH)3(s) 2Na3PO4(aq) 3CaCl2(aq)?
Ca3(PO4)2(s) 6NaCl(aq) 6Na(aq) 2PO43(aq)
3Ca2(aq) 6Cl(aq) ? Ca3(PO4)2(s) 6Na(aq)
6Cl(aq) Net 2PO43(aq) 3Ca2(aq) ?
Ca3(PO4)2(s) 2Na(aq) S2(aq) 2Ag(aq)
2C2H3O2(aq) ? 2Na(aq) 2C2H3O2(aq)
Ag2S(s) Net S2(aq) 2Ag(aq) ? Ag2S(s)
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Solubility

• Precipitation refers to the formation of a solid
  from ions. A precipitate is insoluble
• Soluble and insoluble are general terms to
  describe how much of a solid dissolves.
• Solubility can be predicted from rules (pg.399)
• These are general rules, based on observation
• To determine solubility, follow the rules in
  order
• Note in rule 4 that sulfate SO42-
• You will not have to memorize these rules, you
  will have to use the rules to predict solubility
• Read over example 11.2 (pg. 400)
• Do 11.26 (435) (list the relevant rule for each)
• Do PE 5 (pg. 400) and 11.28 (pg. 435)

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Precipitation

• Precipitation refers to the formation of a solid
  from ions
• Metathesis refers to double displacement
• AB CD ? AD CB
• A metathesis involving ions going to one or more
  solids, is called precipitation
• AB(aq) CD(aq) ? AD(s) CB(aq)
• Recall aq indicates the compound is aqueous (as
  ions)

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Solubility - 11.26

• a) Ca(NO3)2 - Soluble
• rule 2 (salts containing NO3- are soluble)
• b) FeCl2 - Soluble
• rule 3 (all chlorides are soluble)
• c) Ni(OH)2 - Insoluble
• rule 5 (all hydroxides are insoluble)
• d) AgNO3 - Soluble
• rule 2 (salts containing NO3- are soluble)
• e) BaSO4 - Insoluble
• rule 4 (Sulfates are soluble, except Ba2)
• f) CuCO3 - Insoluble
• rule 6 (containing CO32- are insoluble)

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Solubility PE 5 (a) - pg. 400

• Ionic
• Ag(aq) NO3-(aq) NH4(aq) Cl-(aq)
• Note combine, in your head, the positive and
  negative ions. If together a pair is insoluble,
  they will form a precipitate (s).
• In this case AgCl is insoluble (rule 3)
• Ag(aq) NO3-(aq) NH4(aq) Cl-(aq)
• ? AgCl(s) NO3-(aq) NH4(aq)
• Net ionic Ag(aq) Cl-(aq) ? AgCl(s)
• If no solid is formed then write N.R.

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Solubility PE 5 (b), (c) - pg. 400

• Ionic
• 2Na(aq) S2 (aq) Pb2(aq) 2C2H3O2(aq)
• In this case PbS is insoluble (rule 6)
• 2Na(aq) S2(aq) Pb2(aq) 2C2H3O2(aq) ?
  PbS(s) 2Na(aq) 2C2H3O2(aq)
• Net ionic Pb2(aq) S2(aq) ? PbS(s)
• Ionic
• Ba2(aq) 2Cl(aq) NH4(aq) NO3(aq)
• In this case all combinations are soluble
• Ba2(aq) 2Cl(aq) NH4(aq) NO3(aq)
• ? Ba2(aq) 2Cl(aq) NH4(aq) NO3(aq)
• Net ionic N.R. (all ions cancel)

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