Example #2

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EXAMPLE #2 Predicting Precipitation Reactions:  Predict whether a precipitate will form when water solutions of barium acetate, BaCl2(aq), and sodium sulfate, Na2SO4(aq), are mixed.  If there is a precipitation reaction, write the complete and net ionic equation that describes the reaction.

### Solution:

Step #1:  Determine the possible products using the general double displacement equation.

AB  +  CD        AD  +  CB

In BaCl2, A is Ba2+, and B is Cl-. In Na2SO4, C is Na+, and D is SO42-. The possible products from the reaction of BaCl2(aq) and Na2SO4(aq) are BaSO4 and NaCl. (Remember to consider charge when you determine the formulas for the possible products.)

BaCl2(aq) + Na2SO4(aq)  to  BaSO4 and NaCl

Step #2:    Predict whether either of the possible products is water insoluble.

According to our solubility guidelines, most sulfates are soluble, but BaSO4 is an exception. It is insoluble and would precipitate from the mixture. Because compounds containing Na+ and Cl- are soluble, NaCl is soluble.

Step #3:    Write the complete equation. (Dont forget to balance the equation.)

BaCl2(aq)  +  Na2SO4(aq)        BaSO4(s)  +  2NaCl(aq)

Step #4:    Write the complete ionic equation, describing the aqueous ionic compounds as ions. Describe the solid as a complete formula.

Ba2+(aq)  +  2Cl-(aq)  +  2Na+(aq)  +  SO42- (aq)
BaSO4 (s)  +  2Na+(aq)  +  2Cl-(aq)

The chloride and sodium ions have the same form on each side of the equation, so they are eliminated as spectator ions.

Ba2+(aq)  +  SO42-(aq)        BaSO4(s)

This is the reaction used in industry to form barium sulfate, which is used in paint preparations and in x-ray photography.

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