CR_Net Ionic Reactions Lesson
Net Ionic Reactions
In order for us to explore chemical reactions more closely, we need to look at them in a different way. The balanced equations we have written in the past are not the complete picture of what is going on in the reaction. These balanced equations are called molecular reactions. In these types of equations all the substances are written as molecules or compounds.
For example, NaCl(aq)+AgNO3(aq)→AgCl(s)+NaNO3(aq) is called a "molecular equation" even though there are no molecules. The reason is because the formulas are shown with no charges even though the compounds contain ions with charges.
The reality is that often reactions take place in solution (symbolized by aq for aqueous), allowing the chemicals to dissolve (if they are able). Remember that in order for a reaction to occur, the particles must collide. When chemicals are in solution, the particles are freer to move around than they would be in another state.
So, if a compound is dissolved in water to form a solution, the ions separate. If we were to look at an ionic compound that is dissolved in water, we would not see individual compound units. Instead, we would see individual ions surrounded by water molecules. Note that most of the time these water molecules act as the vessel and do not actually participate in the reaction. When an aqueous chemical is involved in a chemical reaction, it is more accurate to write ions instead of the compound.
To begin writing ionic reactions, first we will write what are called dissociation reactions. Dissociation is the breaking apart of an ionic compound when dissolved in water. Remember that the water acts as the vessel, but is usually not written in the equation.
When regular chemical reactions are written using ions, we call them ionic equations. Watch this video to learn how to write ionic equations as well as net ionic equations.
Here is another example using the same process (as explained in the video above) to write a net ionic equation.
Now, let's apply the solubililty rules you learned earlier to write a net ionic equation.
What Should be Written as Ions?
So far you have learned that salts that are dissolved are written as ions. What else should be written this way? Strong acids and bases should also be written as ions. The term strong refers to the extent that the chemical breaks into the ions. Strong acids and bases break completely, or almost completely, into their ions. We have been assuming that in every reaction we have talked about that all of the reactants turn into products. But, this is not always true. In weak acids and bases, the majority of the reactants remain as reactants. So, they will not be written as ions.
The easiest way to remember which acids and bases should be written as ions is to memorize the list of strong acids and bases.
Here is a list of the substances that are NOT written as ions:
- Elements in their natural state (ex. H2)
- Molecules (ex. NH3 or C6H12O6, sugar)
- Non-soluble compounds (use solubility rules to determine this)
- Weak acids and bases (such as acetic acid and ammonia)
- Any other non-electrolyte
- Solids
- Pure liquids
- Gases (memorize the list given earlier)
Watch this video to see lots of examples of writing net ionic equations.
You should not only watch - you should try these reactions along with the teacher. Writing net ionic equations takes practice. The more you do, the easier it will get. You will not only use the concepts learned on this page, but you will also apply concepts you learned about specific reactions on previous pages. It would be an excellent idea to go back through your notes (or the content pages) and make a complete list of reactions.
Remember to work on the module practice problems as you complete each section of content.
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