Spectator ion

Spectator ions are ions that are present in soiutions but are unchanged by whatever chemicai reactions are taking piace in the soiution. 

In the case of precipitation reactions, we can identify which ions did not react using the solubility rules. We call these ions spectator ions. In a football stadium, the action is taking place on the playing field. The spectators are sitting in the stands. The spectators are present in the stadium but do not participate in the action taking place on the field. Spectator ions are like that—they are present in the solution but do not participate in the reaction that is taking place. Thus, a net ionic equation is one that leaves out any spectator ions that might be present. 

The whole idea of a net ionic equation is to show only the ions and molecules that actually react. Any other ions that are present just to give solutions net neutral charges are called spectator ions and are left out of the net ionic equation. 

The ions listed in solubility rule 1 are always spectator ions in all precipitation reactions. Therefore, we would never write a net ionic equation that contains Na+, K+, NHJ,  

CjHjOi CIO3, CIO4 or NO 3. The negative ions listed in rules 2-9 could be spectator ions in some precipitation reactions, but they are not spectator ions in all precipitation reactions. For example, using rule 2, in the reaction between AgNOj and KCl, we would write the following net ionic equation  

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Writing the equation in the usual way directs too much attention to the atoms and not enough to the electrons We can remedy that by deleting any spec tator ions and by showing the unshared electron pairs and covalent bonds that are made and broken Both sodium hydroxide and sodium fluoride are com pletely ionized in water therefore Na" which ap pears on both sides of the equation is a spectator ion Hydrogen fluoride is a weak acid and exists as undissociated HF molecules in water... 

Equations such as this that exclude spectator ions, which take no part in the reaction, are Spectator ions are in solution before,... 

The Na+ and N03 ions take no part in the reaction and so do not appear in the equation. Here again, we are dealing with spectator ions. ... 

Here, as always, spectator ions such as Na+ are not included in the net ionic equation. 

Most anions behave this way, except those derived from strong acids (Cl-, Br-, I-, N03 , C104-), which show little or no tendency to react with water to harm OH- ions. Like the cations listed in the left column of Table 13.5, they act as spectator ions as far as pH is concerned. 

Spectator ion An ion that, although present, takes no part in a reaction, 279,82-83, 372-373,399 Spontaneity of reaction concentration and, 465-467,475-476q entropy and, 453-458 free energy and, 458-471 pressure effects, 465-467,475-476q process, 451-453 redox, 489-490... 

FIGURE 1.5 (a) Silver chloride precipitates immediately when sodium chloride solution is added to a solution of silver nitrate, (b) If we imagine the removal of the spectator ions from the complete ionic reaction (top), we can focus on the essential process, the net ionic reaction (bottom). 

Because the Na+ and N03 ions appear as both reactants and products, they play no direct role in the reaction. They are spectator ions, ions that are present while the reaction takes place but remain unchanged, like spectators at a sports event. Because spectator ions remain unchanged, we can simplify the chemical equation by canceling them on each side of the arrow in the ionic equation ... 

Canceling the spectator ions leaves the net ionic equation for the reaction, the chemical equation that displays the net change taking place in the reaction ... 

STRATEGY First, write and balance the complete ionic equation, showing all the dissolved ions as they actually exist in solution, as separate, charged ions. Insoluble solids are shown as complete compounds. Next, cancel the spectator ions, the ions that remain in solution on both sides of the arrow. 

A complete ionic equation expresses a reaction in terms of the ions that are present in solution a net ionic equation is the chemical equation that remains after the cancellation of the spectator ions. 

Table 1.1 summarizes the solubility patterns of common ionic compounds in water. Notice that all nitrates and all common compounds of the Group 1 metals are soluble so they make useful starting solutions for precipitation reactions. Any spectator ions can be used, provided that they remain in solution and do not otherwise react. For example, Table 1.1 shows that mercury(I) iodide, Hg2I2, is insoluble. It is formed as a precipitate when solutions containing Hg22+ ions and I ions are mixed ... 

Because the spectator ions are not shown, the net ionic equation will be the same when any soluble mercury(I) compound is mixed with any soluble iodide. 

When the solution in Beaker 1 is mixed with the solution in Beaker 2, a precipitate forms. Using the following table, write the net ionic equation describing the formation of the precipitate, and then identify the spectator ions. 

The contents of Beaker 1 are mixed with those of Beaker 2. If a reaction takes place, write the net ionic equation and indicate the spectator ions. ... 

Each of the following five procedures results in the formation of a precipitate. For each reaction, write the chemical equations describing the formation of the precipitate the overall equation, the complete ionic equation, and the net ionic equation. Identify the spectator ions. 

A1P04, used in cements and as an antacid (c) iron(II) hydroxide, Fe(OH)2 (d) Select two soluble ionic compounds that, when mixed in solution, form each of the insoluble compounds in parts (a), (b), and (c). Identify the spectator ions. 

A note on good practice The oxides and hydroxides of the alkali and alkaline earth metals are not Bronsted bases the oxide and hydroxide ions they contain are the bases (the cations are spectator ions). However, for convenience, chemists often refer to the compounds themselves as bases. 

FIGURE 11.15 If the concentration of one of the ions of a slightly soluble salt is increased, the concentration of the other decreases to maintain a constant value of Ksp. (a) The cations (pink) and anions (green) in solution, (b) When more anions are added (together with their accompanying spectator ions, which are not shown), the concentration of cations decreases. In other words, the solubility of the original compound is reduced by the presence of a common ion. In the insets, the blue background represents the solvent (water). 

Deducing ionic equations from observed chemical changes, not by mechanically cancelling out spectator ions in chemical equations. 

The K+ andN03 ions remain unchanged in aqueous solution as spectator ions . All ions involved in the reaction must be represented in the ionic equation. 

The spectator ions are different in both the chemical reactions. 

Third, students understanding of the triplet relationship for a particular type of reaction may be further consolidated by carrying out additional similar reactions using different reactants (e.g., using several metal oxides to react with different dilute acids will help illustrate the similarities in the chemical reactions although different salts are produced). Once students become aware of the similarities in the chemical reactions, they would be more likely to meaningfully deduce the ionic equations for the chemical reactions instead of the common practice of cancelhng out the spectator ions from the overall balanced chemical equation. 

A net ionic equation contains only those species that participate in a chemical reaction. Notice that neither K nor Cr appears in the equation for the precipitation of Fe (OH). Similarly, neither K nor NO3 appears in the equation for the precipitation of Pbl2. Although these other ions are present in the solution, they undergo no change during the precipitation reaction. Ions that are not involved in the chemical change are referred to as spectator ions. Spectator ions are omitted from net ionic equations. 

Mixing the two solutions will produce 2.50 X 10 mol of Fe (0H)3 precipitate, which is 2.67 g. The mixed solution contains Na cations and Cl anions, too, but we can ignore these spectator ions in our calculations. Notice that this precipitation reaction is treated just like other limiting reactant problems. Examples and further illustrate the application of general stoichiometric principles to precipitation reactions. 

Our target was 1.0 kg of product, and we start with slightly more than 1.0 kg of each reactant. That makes sense, because some of the mass of the starting materials is due to spectator ions, Na" and Cl". An attractive feature of this s Tithesis is that these ions, which remain in solution, are non toxic. 

Titration of HCl by NaOH. Spectator ions have been omitted for clarity, (a) Initially, the HCl solution... 

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