Anne Arundel Community College Home Page

Exchange Reactions  What are the Products? / Will it Occur? 

An exchange reaction (also called a double displacement reaction or a metathesis reaction) is a reaction in aqueous solution between two compounds which are acids, bases, or salts.  The cation from the first compound joins with the anion from the second compound, to form one of the products.  The second product is from the anion of the first compound and the cation of the second.

An exchange reaction will occur if one of the products is an insoluble solid (precipitate), a gas, a nonelectrolyte, or a weak electrolyte.  These are the driving forces.  Refer to other review pages for help determining which physical state the compounds are and whether they are strong or weak or nonelectrolytes.

EXAMPLES:  Write a balanced molecular equation for each of the following aqueous reactions.  Indicate whether or not the reaction will occur, and briefly explain why.

(1)   ammonium phosphate  +  calcium acetate

  reactant 1 reactant 2

--->

 product 1 product 2
cation NH41+ Ca2+ NH41+ Ca2+
anion PO43- C2H3O21- C2H3O21- PO43-
compound (NH4)3PO4 Ca(C2H3O2)2 NH4C2H3O2 Ca3(PO4)2
state (aq) (aq) (aq) (s)

Answer:

2 (NH4)3PO4(aq)  + 3 Ca(C2H3O2)2(aq)   --->  6 NH4C2H3O2(aq)  +   Ca3(PO4)2(s)

An insoluble solid is formed, so this reaction DOES occur.

(2)   calcium hydroxide  +  perchloric acid

  reactant 1 reactant 2

--->

 product 1 product 2
cation Ca2+ H1+ Ca2+ H1+
anion OH1- ClO41- ClO41- OH1-
compound Ca(OH)2 HClO4 Ca(ClO4)2 H2O
state (aq) (aq) (aq) (l)

Answer:

Ca(OH)2(aq)  + 2 HClO4(aq)   --->  Ca(ClO4)2(aq)  +   2H2O(l)  

A nonelectrolyte (water) is formed, so this reaction DOES occur.

PRACTICE EXERCISES:

Write a balanced molecular equation for each of the following aqueous reactions.  Indicate whether or not the reaction will occur, and briefly explain why.

QUESTIONS:

1. barium chloride  +  copper(II) sulfate
2. gold(III) nitrate  +  strontium hydroxide
3. aluminum iodide  +  lead(II) acetate
4. sodium hydroxide  +  nitric acid
5. acetic acid  +  calcium hydroxide
6. hydrobromic acid  +  barium sulfide
7. iron(III) acetate  +  calcium sulfate
8. mercury(I) nitrate  +  sodium bromide
9. rubidium phosphate  +  chromium(III) chloride

1:00-2:00

ANSWERS (If you do not understand any of these, the go ask your instructor) :

1. BaCl2(aq) + CuSO4(aq)  -->  BaSO4(s) + CuCl2(aq)
YES this reaction occurs, because an insoluble solid is formed.
2. 2 Au(NO3)3(aq) + 3 Sr(OH)2(aq)  -->  2 Au(OH)3(s) + 3 Sr(NO3)2(aq)
YES this reaction occurs, because an insoluble solid is formed.
3. 2 AlI3(aq) + 3 Pb(C2H3O2)2(aq)  -->  2 Al(C2H3O2)3(aq) + 3 PbI2(s)
YES this reaction occurs, because an insoluble solid is formed.
4. NaOH(aq) + HNO3(aq)  -->  NaNO3(aq) + H2O(l) 
YES this reaction occurs, because a nonelectrolyte is formed.
5. 2 HC2H3O2(aq) + Ca(OH)2(aq)  -->  2 H2O(l) + Ca(C2H3O2)2(aq)
YES this reaction occurs, because a nonelectrolyte is formed.
6. 2 HBr(aq) + BaS(aq)  -->  H2S(g) + BaBr2(aq)
YES this reaction occurs, because a gas is formed.
7. 2 Fe(C2H3O2)3(aq) + 3 CaSO4(aq)  -->  Fe2(SO4)3(aq) + 3 Ca(C2H3O2)2(aq)
NO this reaction does not occur, because none of the driving forces is present - all of the products are soluble strong electrolytes.
8. Hg2(NO3)2(aq) + 2 NaBr(aq)  -->  Hg2Br2(s) + 2 NaNO3(aq)
YES this reaction occurs, because an insoluble solid is formed.
9. Rb3PO4(aq) + CrCl3(aq)  -->  3 RbCl(aq) + CrPO4(s)
YES this reaction occurs, because an insoluble solid is formed.

Tutoring Cent

last updated 14 December 2008