Complete-Formula Equations
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Complete-Formula Equations

Let's work with these combinations of ions from exercise 9 in your workbook.
Ba2+
NO3-
Cu2+
SO42-
   
The compound that contains both barium and nitrate ions is called barium nitrate and has the formula Ba(NO3)2. The compound that contains both copper(II) ions and sulfate ions is called copper(II) sulfate (or cupric sulfate) and has the formula CuSO4.
barium nitrate copper(II) sulfate    
Ba(NO3)2 CuSO4    
When these compounds react with one another we get a double displacement reaction and the products are barium sulfate and copper(II) nitrate. The formulas are BaSO4 and Cu(NO3)2.

Ba(NO3)2 + CuSO4 rtarrow.gif (850 bytes) BaSO4 + Cu(NO3)2

To balance this equation we have to make sure that we have the same number of bariums, nitrates, coppers, and sulfates on each side of the equation. We do, so the equation is balanced. 
Please note that it is a coincidence that each formula contains two nitrate ions.  This is because both barium and copper ions have a charge of +2.

Precipitation reactions are often represented using complete-formula equations. Their advantage is that they show the compounds that are involved. Their disadvantage is that they do not show the forms of the chemicals that are actually involved in the reaction. (Sometimes these equations are called "molecular" equations, even though the compounds are ionic rather than molecular.)

Practice

Now please do exercise 9 in your workbook and check your answers below before continuing with the lesson.

Answers

These are the complete-formula equations for the reactions in which precipitates are predicted in Exercise 9. The precipitates are marked as (ppt).

CuSO4 + Ba(NO3)2 rtarrow.gif (850 bytes) Cu(NO3)2 + BaSO4(ppt)

copper(II) sulfate + barium nitrate rtarrow.gif (850 bytes) copper(II) nitrate + barium sulfate

 

CuSO4 + 2 AgNO3 rtarrow.gif (850 bytes) Cu(NO3)2 + Ag2SO4(ppt)

copper(II) sulfate + silver nitrate rtarrow.gif (850 bytes) copper(II) nitrate + silver sulfate

 

CuSO4 + 2 NaOH rtarrow.gif (850 bytes) Cu(OH)2(ppt) + Na2SO4

copper(II) sulfate + sodium hydroxide rtarrow.gif (850 bytes) copper(II) hydroxide + sodium sulfate

 

Ba(NO3)2 + 2 NaOH rtarrow.gif (850 bytes) Ba(OH)2(ppt) + 2 NaNO3

barium nitrate + sodium hydroxide rtarrow.gif (850 bytes) barium hydroxide + sodium nitrate

 

AgNO3 + NaOH rtarrow.gif (850 bytes) AgOH(ppt) + NaNO3

silver nitrate + sodium hydroxide rtarrow.gif (850 bytes) silver hydroxide + sodium nitrate

 

AgNO3 + KCl rtarrow.gif (850 bytes) AgCl(ppt) + KNO3

silver nitrate + potassium chloride rtarrow.gif (850 bytes) silver chloride + potassium nitrate

 

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