Chapter 7: Reactions in aqueous solutions

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Chapter 7 Reactions in aqueous solutions
Chemistry 1020 Interpretive chemistry Andy
Aspaas, Instructor
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Reactions in which a solid forms

• Precipitation formation of a solid in a chemical
  reaction (a precipitation reaction)
• Precipitate the solid that forms
• Whether a precipitate forms or not depends
  strongly on the solubility of that compound
  (ability of a compound to dissolve in water)

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Process of ionic compounds dissolving in water

• If an ionic compound dissolves in water, its
  positive and negative ions separate and move
  independently
• Strong electrolyte an ionic compound whose ions
  separate completely when dissolved in water, and
  therefore conducts electricity
• Molecular substances like sugar are not strong
  electrolytes even though theyre soluble in water
• Electrolytes must be made of ions!

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Precipitation reactions

• When two strong electrolytes are mixed together,
  all the ions are mixed
• Any /- combinations of ions in the solution can
  form products
• To predict possible products of a precipitation
  reaction, separate the reactants into their
  component ions, and swap partners to form new
  products
• AgNO3(aq) KI(aq) ? ?

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Precipitation reactions

• But simply predicting the products of a
  precipitation reaction does not predict whether a
  visible reaction will occur or not
• You must determine the solubility of the products
• If all products are soluble in water, no reaction
  will have occurred
• If one or more products are insoluble, they are
  the precipitate that has formed

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Solubility rules

• A soluble compound is one which readily and
  completely dissolves in water (the ions separate
  and disperse)
• An insoluble or slightly soluble compound is
  one which, for the most part, does not dissolve
  in water
• Solubility rules allow us to predict whether a
  compound is soluble or insoluble

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Solubility rules

• Predict the solubility
• CaSO4
• MgCl2
• NaOH
• LiOH
• CuSO4
• AlPO4
• AgI
• NH4C2H4O4

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Using solubility rules to predict precipitation

• Solubility rules can be used to assign phase
  labels to all constituents of a reaction
• Insoluble compounds are solid (s)
• Soluble compounds are aqueous (aq)
• If all compounds in a reaction are aqueous, no
  reaction has occurred (NR)

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Predict the products

• NH4Cl H2SO4 ?
• K3PO4 AlCl3 ?
• CuSO4 KOH ?
• Sodium carbonate and barium nitrate
• Ammonium sulfide and cobalt(II) chloride
• Sodium hydroxide and iron(III) chloride

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Describing aqueous reactions

• Molecular equation show ionic formulas of all
  reactants and products
• Complete ionic equation any soluble (aq)
  compound is shown as its component ions
• Aqueous sodium chloride
• NaCl(aq) in molecular equation
• Na(aq) Cl(aq) in complete ionic equation
• Other compounds (s), (l), or (g) remain as they
  would in molecular equation

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Net ionic equations

• Spectator ions ions which do not participate in
  the reaction
• Exist as ionic form on both products and
  reactants side of the equation
• Net ionic equation ionic equation with no
  spectator ions

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Practice writing equations

• Write the molecular, complete ionic, and net
  ionic equations for the following reactions
• Mixture of potassium sulfide and calcium nitrate
• Mixture of nickel(II) sulfate and barium chloride