A spectator ion is an
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
that exists as a
reactant
In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...
and a
product
Product may refer to:
Business
* Product (business), an item that serves as a solution to a specific consumer problem.
* Product (project management), a deliverable or set of deliverables that contribute to a business solution
Mathematics
* Produ ...
in a
chemical equation
A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and chemical formulas. The reactant entities are given on the left-hand side and the product entities on the right-hand side with a plus sign between ...
. A spectator ion can, therefore, be observed in the reaction of
aqueous solutions of
sodium carbonate and
copper(II) sulfate
Copper(II) sulfate, also known as copper sulphate, is an inorganic compound with the chemical formula . It forms hydrates , where ''n'' can range from 1 to 7. The pentahydrate (''n'' = 5), a bright blue crystal, is the most commonly encountered h ...
but does not affect the equilibrium:
:2
( aq) +
(aq) +
(aq) +
(aq) → 2
(aq) +
(aq) +
( s)
The and ions are spectator ions since they remain unchanged on both sides of the equation. They simply "watch" the other ions react, hence the name. They are present in total ionic equations to balance the charges of the ions. Whereas the and ions combine to form a
precipitate
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
of solid . In
reaction stoichiometry, spectator ions are removed from a complete ionic equation to form a net ionic equation. For the above example this yields:
So:
2 (aq) +
(aq) +
(aq) +
(aq) →
2 (aq) +
(aq) +
(s) (where
x = spectator ion)
:⇒
(aq) +
(aq) →
(s)
Spectator ion concentration only affects the
Debye length
In plasmas and electrolytes, the Debye length \lambda_ (also called Debye radius), is a measure of a charge carrier's net electrostatic effect in a solution and how far its electrostatic effect persists. With each Debye length the charges are in ...
. In contrast,
potential determining ions, whose concentrations affect surface potential (by surface chemical reactions) as well the Debye length.
Net ionic equation
A net ionic equation ignores the spectator ions that were part of the original equation. Therefore, the total ionic reaction is different from the net reaction.
See also
*
Catalysis
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
Acid–base chemistry
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