AP Chemistry Predicting Products Tutorial

Answers to Double Replacement #1-15

I. DOUBLE REPLACEMENT

Dilute sulfuric acid is added to a solution of barium acetate.

H+`+`SO42- + Ba2+ + C2H3O2- BaSO4 + HC2H3O2

Ammonium chloride crystals are added to a solution of sodium hydroxide.

NH4Cl + Na+ + OH- Na+ + Cl- + NH4OH Na+ + Cl- + NH3 + H2O

Net ionic: NH4Cl + OH- Cl- + NH3 + H2O

A precipitate is formed when solutions of trisodium phosphate and calcium chloride are mixed.

3Na+ + 2PO43- + 3Ca2+ + 2Cl- Ca3(PO4)2 + 3Na+ + 2Cl-

net ionic: 2PO43- + 3Ca2+ Ca3(PO4)2

Equal volumes of 0.1 M hydrochloric acid and 0.1 M disodium hydrogen phosphate are mixed.

2H+ + 2Cl- + 2Na+ + HPO42- H2PO4 + 2Na+ + 2Cl-

net ionic: 2H+ + HPO42- H2PO4

Hydrogen sulfide gas is bubbled through a solution of lead(II) nitrate.

H2S + Pb2+ + 2NO3- PbS + 2H+ + 2NO3-

Net ionic: H2S + Pb2+ PbS + 2H+

Solutions of silver nitrate and sodium chromate are mixed.

2Ag+ + NO3- + 2Na+ + CrO42- Ag2CrO4 + 2Na+ + NO3-

Net ionic: 2Ag+ + CrO42- Ag2CrO4

Solutions of sodium fluoride and dilute hydrochloric acid are mixed.

Na+ + F- + H+ + Cl- HF + Na+ + Cl-

Net ionic: F- + H+ HF

A saturated solution of barium hydroxide is mixed with a solution of iron(III) sulfate.

Ba2+ + 6OH- + 2Fe3+ + SO42- 2Fe(OH)3 + BaSO4

A solution of ammonium sulfate is added to a potassium hydroxide solution.

NH4+ + SO42- + 2K+ + OH- 2K+ + SO42- + NH4OH 2K+ + SO42- + NH3 + H2O

Net ionic: NH4+ + OH- NH3 + H2O

A solution of ammonium sulfate is added to a saturated solution of barium hydroxide.

2NH4+ + SO42- + Ba2+ + 2OH- BaSO4 + NH4OH BaSO4 + 2NH3 + 2H2O

Net ionic: 2NH4+ + SO42- + Ba2+ + 2OH- BaSO4 + 2NH3 + 2H2O

A drop of potassium thiocyanate is added to a solution of iron(III) chloride.

3K+ + 3SCN- + Fe3+ + 3Cl- Fe(SCN)3 + 3K+ + 3Cl-

net ionic: 3SCN- + Fe3+ Fe(SCN)3

Note: Fe(SCN)3 must have precipitated out, because otherwise everything would have cancelled resulting in “No Reaction”. That would never happen on the AP Test. If you are getting everything to cancel out you must be doing something wrong. SCN- is not on your list of insolubles simply because it doesn’t show up very often, but this is a case where you should have been able to figure out it must have been insoluble even though it wasn’t told to you as being so.

Dilute sulfuric acid is added to solid calcium fluoride.

2H+ + SO42- + CaF2 CaSO4 + 2HF

Dilute hydrochloric acid is added to a dilute solution of mercury(I) nitrate.

H+ + 2Cl- + Hg22+ + NO3- Hg2Cl2 + H+ + NO3-

Net ionic: Hg22+ + 2Cl- Hg2Cl2

Note: Be very careful with the mercury compounds. Hg2Cl2 is insoluble while HgCl2 is soluble. Since mercury(I) is Hg22+, you’ll end up with Hg2Cl2 as a precipitate. And of course, it must have precipitated out in order to have a reaction as noted in #11 above.

A solution of ammonium chloride is added to a dilute solution of mercury(I) nitrate.

NH4+ + 2Cl- + Hg22+ + NO3- Hg2Cl2 + NH4+ + NO3-

Net ionic: 2Cl- + Hg22+ Hg2Cl2

Solid cupric sulfide is warmed with 6 N nitric acid.

CuS + 2H+ + 2NO3- H2S + Cu2+ + 2NO3-

Net ionic: CuS + 2H+ H2S + Cu2+

Note: 6 N is a way of representing concentration in terms of normality. We have not covered normality yet; the N is not a typo.

****What do you notice about what happens when NH4OH is formed (See #2, #9 and #10)? Also see your “Stuff I should know for the AP test but do not know yet” for a hint. Make sure you are looking over all of the information given to you on that sheet.