Determining if a compound is soluble (aq) or NOT LOOK AT TABLE F –LiOH –Cu(NO 3 ) 2 –AgCl 2 –MgS –NaS 2 –KOH –aq –insoluble = precipitate = s –aq

Double Replacement Reactions

Double Replacement Format: AX + BY  AY + BX

DR rns occur in aqueous solutions So, what exactly happens to a substance when we put it in water? –depends if ionic or covalent

Dissolving sugar molecules spread out among water molecules Covalent substance – ex: sugar (C 6 H 12 O 6 ) C 6 H 12 O 6 (s)  C 6 H 12 O 6 (aq)

Dissolving Ionic substance – ex: table salt (NaCl) NaCl(s)  Na +1 (aq) + Cl -1 (aq) ions spread out among water molecules

Double Replacement Reactions occur with 2 ionic compound solutions Products can be: - liquid (H 2 O) -- gas -- solid Reactions producing solids Precipitation: solid is formed - opposite of dissolving! MOVIE

EX: Reactions producing Solids 2 NaOH(aq) + CuCl 2 (aq)  2 NaCl(aq) + Cu(OH) 2 (s) This is the Chemical Equation but it’s not the whole story…

In solution it’s not NaOH and CuCl 2 You actually have ions floating around in water Reactants: 2Na +1 (aq) + 2OH -1 (aq) + Cu 2+ (aq) + 2Cl -1 (aq) Products: 2Na +1 (aq) + 2Cl -1 (aq) + Cu(OH) 2 (s) ions in solution are written as aqueous O HH Na +1 Cu 2+ O HH O HH O HH O HH Na +1 Cl +1 Cl -1 Cl +1 H O H O H O 2 NaOH(aq) + CuCl 2 (aq)  2 NaCl(aq) + Cu(OH) 2 (s) Cu H O H O H O

Net Ionic Equations 2Na +1 (aq) + 2OH -1 (aq) + Cu 2+ (aq) + 2Cl -1 (aq)  2Na +1 (aq) + 2Cl -1 (aq) + Cu(OH) 2 (s) Notice some ions do not participate in reaction = spectator ions cross out spectator ions to get net ionic equation Here’s what is really involved in the reaction… 2OH -1 (aq) + Cu 2+ (aq)  Cu(OH) 2 (s) 2 NaOH(aq) + CuCl 2 (aq)  2 NaCl(aq) + Cu(OH) 2 (s)

Double Replacement Reactions occur with 2 ionic compound solutions Products can be: - liquid (H 2 O) -- gas -- solid

Reactions that form Water HBr(aq) + NaOH(aq)  H 2 O(l) + NaBr(aq) H +1 (aq) + Br -1 (aq) + Na +1 (aq) + OH -1 (aq)  H 2 O(l) + Na +1 (aq) + Br -1 (aq) H +1 (aq) + OH -1 (aq)  H 2 O(l)

Reactions that form Gases HCl(aq) + NaHCO 3 (aq)  H 2 CO 3 (aq) + NaCl(aq) H 2 O(l) + CO 2 (g)

Reactions that form Gases HCl(aq) + NaHCO 3 (aq)  H 2 O(l) + CO 2 (g) + NaCl(aq) H +1 (aq) + Cl -1 (aq) + Na +1 (aq) + HCO 3 -1 (aq)  H 2 O(l) + CO 2 (g) + Na +1 (aq) + Cl -1 (aq) H +1 (aq) + HCO 3 -1 (aq)  H 2 O(l) + CO 2 (g)

Conservation of Charge total charge (reactant side) must equal total charge on product side 2OH -1 (aq) + Cu 2+ (aq)  Cu(OH) 2 (s) -1 x = 0 H +1 (aq) + OH -1 (aq)  H 2 O(l) H +1 (aq) + HCO 3 -1 (aq)  H 2 O(l) + CO 2 (g)H +1 (aq) + HCO 3 -1 (aq)  H 2 O(l) + CO 2 (g)