What are the molecular, complete ionic, and net ionic equations for the reaction between lead(II) nitrate and ammonium phosphate?

1 Answer
Meave60
Sep 17, 2014

If you are being asked to find the molecular, complete ionic, and net ionic equations, you are dealing with a double replacement/displacement reaction. I will continue answering the question using the term double replacement, though displacement is just as valid.

During double replacement reactions, the cations (positively charged ions) and anions (negatively charged ions) of two different compounds switch places. The generic equation is AB + XY #rarr# AY + XB, where A and X are the cations, and B and Y are the anions. The products of a double replacement reaction must include a precipitate (insoluble solid), water, or gas.

The ions involved in this reaction are lead (II), #"Pb"^"2+"(aq)"#, nitrate, #"NO"_3^-"(aq)#, ammonium, #"NH"_4^+"(aq)"#, and phosphate, #"PO"_4"^(3-)(aq)#.

The molecular equation between lead nitrate and ammonium phosphate is:

#"3Pb(NO"_3")"_2""(aq)"# + #"2(NH"_4")"_3"PO"_4"(aq)"# #rarr# #"Pb"_3""("PO"_4")"_2"("s")# + #"6NH"_4"NO"_3"(aq)#

The word equation for this reaction is: Three moles of aqueous lead (II) nitrate plus two moles of aqueous ammonium phosphate produce one mole of solid lead phosphate plus six moles of ammonium nitrate. Since one of the products is an insoluble solid (precipitate), this is a double replacement reaction.

The complete ionic equation includes all of the ions and the precipitate.

#"3Pb"^"2+"(aq)"# + #"6NO"_3^-"(aq)# + #6"NH"_4^+"(aq)"# + #"2PO"_4"^(3-)(aq)# #rarr# #"Pb"_3""("PO"_4")"_2"("s")# + #"6NH"_4^+"(aq)# + #"6NO"_3^-"(aq)#

The net ionic equation includes only the ions that reacted to form the precipitate, and the precipitate.

#"3Pb"^"2+"(aq)"# + #"2PO"_4"^(3-)(aq)# #rarr# #"Pb"_3""("PO"_4")"_2"("s")#

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