spectator ion

Examples of spectator ion in the following topics:

• Precipitation Reactions

  • Precipitation reactions transform ions into an insoluble salt in aqueous solution.
  • This reaction can be also be written in terms of the individual dissociated ions in the combined solution.
  • In this case, any spectator ions (those that do not contribute to the precipitation reaction) are left out of the formula completely.
  • Without the spectator ions, the reaction equation simplifies to the following:
  • Observing precipitation reactions can be useful in the laboratory to determine the presence of various ions in solution.

• Molecular, Ionic, and Complete Ionic Equations

  • In this equation, every ion is written out on both sides.
  • The equation is balanced with the molar amount of each ion preceding it.
  • The $Ca^{2+}$$NO_{3}^{-}$and the ions remain in solution and are not part of the reaction.
  • They are termed spectator ions because they do not participate directly in the reaction; rather, they exist with the same oxidation state on both the reactant and product side of the chemical equation.
  • Silver chloride is a precipitant of silver and chloride ions reacting in solution.

• Electrochemical Cell Notation

  • In the reaction, the silver ion is reduced by gaining an electron, and solid Ag is the cathode.
  • Spectator ions are not included.

• Predicting Precipitation Reactions

  • Let's see how the ions in this example could have combined with each other:
  • Notice how the sodium and chloride ions remain unchanged during the reaction.
  • They are called spectator ions.
  • The possible combinations of the ions are as follows:
  • Even when the ions recombine, they immediately separate and go back into solution.

• Balancing Redox Equations

  • Notice that the sulfate ion (SO42-) is ignored.
  • This is because it does not take part in the reaction; it is a spectator ion.
  • If the hydrogen atoms are not balanced, add hydrogen ions (H+).
  • Then, combine the hydroxide and hydrogen ions to form water.
  • If the hydrogen atoms are not balanced, add hydrogen ions (H+).

• Ion-Dipole Force

  • The ion-dipole force is an intermolecular attraction between an ion and a polar molecule.
  • However, ion-dipole forces involve ions instead of solely polar molecules.
  • Ion-dipole forces are stronger than dipole interactions because the charge of any ion is much greater than the charge of a dipole; the strength of the ion-dipole force is proportionate to ion charge.
  • An ion-induced dipole force occurs when an ion interacts with a non-polar molecule.
  • Ion-dipole forces are generated between polar water molecules and a sodium ion.

• Lewis Structures for Polyatomic Ions

  • Lewis structures for polyatomic ions are drawn by the same methods that we have already learned.
  • When counting electrons, negative ions should have extra electrons placed in their Lewis structures; positive ions should have fewer electrons than an uncharged molecule.
  • Negative ions follow the same procedure.
  • The chlorite ion, ClO2–, contains 19 (7 from the Cl and 6 from each of the two O atoms) +1 = 20 electrons.
  • The hypochlorite ion, ClO−, contains 13 + 1 = 14 electrons.

• Ion Channels

  • Ion channels are membrane proteins that allow ions to travel into or out of a cell.
  • Each of these channels are selective as to the type of ion or ions that it allows to pass across the membrane.
  • Most channels are specific (selective) for one ion.
  • Ion pumps are not ion channels but are critical membrane proteins that carry out active transport by using cellular energy (ATP) to "pump" the ions against their concentration gradient.
  • A schematic representation of an ion channel.

• Characteristics of Mass Spectra

  • The highest-mass ion in a spectrum is normally considered to be the molecular ion, and lower-mass ions are fragments from the molecular ion, assuming the sample is a single pure compound.
  • The molecular ion is the strongest ion in the spectra of CO2 and C3H6, and it is moderately strong in propane.
  • The molecular ion is also the base peak, and the only fragment ions are CO (m/z=28) and O (m/z=16).
  • The molecular ion of propane also has m/z=44, but it is not the most abundant ion in the spectrum.
  • As a rule, odd-electron ions may fragment either to odd or even-electron ions, but even-electron ions fragment only to other even-electron ions.

• The Common Ion Effect

  • The common ion effect describes the changes that occur with the introduction of ions to a solution containing that same ion.
  • The common ion effect can be explained by Le Chatelier's principle of chemical equilibrium:
  • For a simple dissolution process, the addition of more of one of the ions (A+) from another compound will shift the composition to the left, reducing the concentration of the other ion (B-), effectively reducing the solubility of the solid (AB).
  • Addition of excess ions will alter the pH of the buffer solution.
  • Therefore, the common ion effect takes a role in pH regulation.