Chemistry Reference
In-Depth Information
Now, try an example on your own, and then check your answer with the
one that I produce. In this example, we will ask for both the ionic equation
and the net ionic equation. If you need help, refer to the example that I
showed you. If you find that you need more help, review Chapter 5 and the
other lessons in Chapter 6.
Example 2
A student mixes aqueous solutions of sodium phosphate and iron (III)
chloride and finds that a yellow-white precipitate forms. For this
chemical reaction:
A. Write a word equation.
B. Write a balanced chemical reaction, with subscripts
indicating state or phase.
C. Write an ionic equation.
D. Write a net ionic equation.
E. Identify the precipitate.
A. The word equation should be relatively simple to write. We have both
reactants already, and we simply swap the negative ions from each com-
pound to find the products, giving us the word equation:
sodium phosphate + iron (III) chloride
sodium chloride + iron (III) phosphate
B.
In order to write the balanced chemical reaction, we need to write the
chemical formulas properly. The stock system tells us that the oxida-
tion number for the iron, as in iron (III) chloride, will be +3. We look
up any of the oxidation numbers that we don't know, and find this
information:
iron (III) = Fe
3+
phosphate = PO
4
3-
chloride = Cl
-
sodium = Na
+
We use this information, and our knowledge of writing chemical
formulas and equations, to write the balanced chemical equation:
Na
3
PO
4(aq)
+ FeCl
3(aq)
3NaCl + FePO
4
Now, we know that the reactants are in solution, because the
original question told us that. You probably already know that one of
the products, NaCl, is soluble, so it should also get the “aq” subscript.
Notice that with this problem, you could predict that the precipitate is
the iron (III) phosphate, even without the solubility rules and Figure
6-3a. To be sure, however, we consult this information when we have
access to them. There we find that iron (III) phosphate is indeed insoluble.
