How to Form Net Ionic Equations

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A chemical equation typically includes the symbols for all of the products and reactants. By convention, the reactants are on the left side of the arrow, the products on the right, e.g. NaCl(aq) + AgNO3(aq) --> NaNO3(aq) + AgCl(s), where (aq) indicates the substance is dissolved while (s) indicates it's a solid. In an equation between ions in solution like this one, however, some of the ions are participants, while others are merely spectators. A net ionic equation lists only the participants and leaves the spectators out. Here's how to write the net equation.

Things You'll Need

  • Pencil
  • Paper
  • Names of reactants and products in the reaction you want to form
  • Write out the chemical equation for the full reaction. Our example is silver nitrate plus sodium chloride, both of them dissolved in water, which runs as follows:

    NaCl(aq) + AgNO3(aq) --> NaNO3(aq) + AgCl(s)

    Notice that silver ions are combining with chloride ions to form an insoluble salt, silver chloride.

  • Remember that when ionic compounds dissolve in water, the ions are no longer associated with each other; they are floating around in the water separately. Consequently, when there is an ionic compound in aqueous solution -- NaCl(aq), for instance -- it would be more accurate to describe it as Na+(aq) + Cl-(aq). When the ionic compound is a solid, by contrast, the two ions are associated with each other as part of the crystal, so AgCl(s) is accurate.

  • Rewrite the chemical equation in ionic form by breaking up each dissolved ionic compound into the ions that would be present in solution. In our example, we would have the following:

    Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq) ---> AgCl(s) + Na+(aq) + NO3-(aq)

  • Look for ions that don't change or combine with other ions during the course of the reaction. In other words, they're the same on the product side as they were on the reactant side. In our example, we notice that Na+ and NO3- are the same on the product side as they are on the reactant side; they haven't exhibited any change. They are both spectator ions that do not participate in the reaction.

  • Rewrite the ionic equation, but leave out all the spectator ions. This will give you the net ionic equation. In our example, we would have the following:

    Ag+(aq) + Cl-(aq) ---> AgCl(s)

Tips & Warnings

  • It's helpful to review your solubility rules when working on these kinds of problems. You can find a list of common solubility rules at the link in the Resources section below.

References

  • Photo Credit Jupiterimages/Pixland/Getty Images
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