Enduring Understanding 3.A.1: Ionic and Net Ionic Equations

• In solution, some ions will participate in a chemical reaction (e.g. forming a precipitate) while others will remain in solution, unchanged. These ions that are unchanged in a reaction are called spectator ions.
• Sometimes, it is useful to remove spectator ions from chemical equations and just write equations with the species that actually react. These are called net ionic equations.

• Example: The reaction of barium nitrate and sodium sulfate solutions to form a barium sulfate precipitate:
• For the reaction: Ba(NO3)2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2NaNO3 (aq)
• The full ionic equation of this reaction shows soluble ionic compounds as separate ions:
• Ba2+ + 2 NO3- + 2 Na+ + SO42- → BaSO4 (s) + 2 Na+ + 2 NO3-
• This is the complete ionic equation. Barium and sulfate ions react to form barium sulfate precipitate, and the sodium and nitrate ions are unchanged - they are spectator ions.
• If we remove the unchanged ions from each side of the equation:
• Ba2+ + 2 NO3- + 2 Na+ + SO42- → BaSO4 (s) + 2 Na+ + 2 NO3-
• If we remove the unchanged ions from each side of the equation:
• Ba2+ + SO42- → BaSO4 (s)
• This is the net ionic equation, showing only the ions involved in the reaction.

• Example 1: What are the spectator ions in the reaction of AgNO3(aq) and KCl(aq) to form an AgCl precipitate?
• Ag+ and Cl- are forming the precipitate, so NO3- and K+ are the spectator ions.

• Example 2: If a solution of sodium bicarbonate is mixed with hydrochloric acid, sodium chloride solution, carbon dioxide, and water are produced. What are the total and net ionic equations?
• The total reaction equation is:
• NaHCO3 (aq) + HCl (aq) → NaCl (aq) + CO2 (g) + H2O (l)
• The total ionic reaction is:
• Na+ + HCO3- + H+ + Cl- → Na+ + Cl- + CO2 (g) + H2O (l)
• Na+ and Cl- are present unchanged on both sides of the equation. The net ionic reaction is therefore:
• HCO3- + H+ → CO2 (g) + H2O (l)

 Related Links: Chemistry Chemistry Quizzes AP Chemistry Notes Balanced Chemical Equations

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