Ppt15, Net Ionic Equations (mainly) PS6 material, continued Reminder, Electrolytes Reminder, Ionic Compounds Reminder, Stoichiometry of Electrolytes Net Ionic Equations → Expressing what really happens Exchange Reactions (Double Displacement Reactions) Ppt15

Ppt15

NaCl (aq)  Na+ (aq) + Cl- (aq) Ionic Compounds dissociate into constituent ions when dissolved hence, they are strong electrolytes if they are soluble “Strong” = ions dissociate stoichiometrically (~100% of FU’s separate) NaCl (aq)  Na+ (aq) + Cl- (aq) K2S (aq)  2 K+ (aq) + S2- (aq) (NH4)2CO3 (aq)  2 NH4+ (aq) + CO32- (aq) CaCO3 (s)  not soluble Ppt15

4

Review How many moles of K+ ions are present in 0.25 L of 0.015 M K2CO3 solution? K2CO3  2 K+(aq) + CO32-(aq) 0.25 L x 0.015 mol x 2 mol K+ = 0.0075 1 L 1 mol K2CO3 mol K+ subscript (ratio) [mol A from mol AxBy] mol K2CO3 [M x V = mol] Ppt15

Acids/Bases/Salts Acids have an ionizable hydrogen, H+ eg. HCl(aq) or HC2H3O2(aq) can be strong or weak electrolytes Ppt15

Strong Acids--know these! HCl, HBr, HI, HNO3, H2SO4, HClO4 Any other acid is therefore WEAK!! Bases substances that react with acids produce hydroxide ions, OH-, in solution can be strong electrolytes (soluble ionic hydroxides) or weak electrolytes (NH3 or similar molecular compounds) NaOH(aq)  Na+(aq) + OH-(aq) NH3(aq) + H2O  NH4+(aq) + OH-(aq) Ppt15

Ppt15

Molecular vs. Ionic Equations Three ways to express chemical equations molecular equation--all species expressed as neutral formulas (regardless of whether substance is molecular or not) HCl(aq) + NaOH(aq)  H2O(l) + NaCl(aq) (HCl(aq) is really H+(aq) and Cl-(aq) in solution) complete ionic equation--all STRONG ELECTROLYTES are expressed in ionic form H+(aq)+ Cl-(aq) + Na+(aq) + OH-(aq)  H2O(l) + Na+(aq) + Cl-(aq) spectator ions: ions that undergo no change Ppt15

NET ionic equation--incl NET ionic equation--incl. only species that change (so cross out any that are on both sides [spectators]) H+(aq) + OH-(aq) ® H2O(l) Remember, only strong electrolytes (i.e., soluble ionic compounds OR strong acids) are written in ionic form! Examples H2S(aq) + 2NaOH(aq) ® 2H2O(l) + Na2S(aq) (molec. eqn) H2S(aq) + 2Na+(aq) + 2OH-(aq) ® 2H2O(l) + 2Na+(aq) + S2-(aq) H2S(aq) + 2OH-(aq) ® 2H2O(l) + S2-(aq) (net ionic eqn) Ppt15

Exchange* Reactions (*Double Displacement) General Form ion partner exchange _AmXn + _BpYq  _ArYs + _BuXv Pb(NO3)2 + K2S  + Driving Forces formation of an insoluble solid [see precipitate] formation of a weak or non-electrolyte [warms] formation of a gas [see bubbles] PbS 2 KNO3 (aq) (aq) (s) (aq) Ppt15

Precipitation Reaction formation of an insoluble solid know the solubility guidelines!! examples: NaCl(aq) + KNO3(aq)  NaNO3(aq) + KCl(aq) AgNO3(aq) + KCl(aq)  ??? Na+ + Cl- + K+ + NO3- ® Na+ + NO3- + K+ + Cl- NOTHING CHANGED!  “no reaction” (just a bunch of ions swimming around in solution!) AgCl + KNO3 aq (soluble) Solid (insoluble) Ag+ + NO3- + K+ + Cl- ® AgCl(s) + K+ + NO3- Ag+(aq) + Cl-(aq) ® AgCl(s) Ppt15

Formation of a weak or non-electrolyte common example is an acid/base reaction--H2O forms know/recognize electrolyte vs non-electrolyte examples: HCl(aq) + NaOH(aq)  H2O(l) + NaCl(aq) NiO(s) + 2HNO3(aq)  Ni(NO3)2(aq) + H2O(l) H+ + Cl- + Na+ + OH- ® H2O + Cl- + Na+ H+ + OH- ® H2O NiO(s) + 2H+ + 2NO3- ® Ni2+ + 2NO3- + H2O NiO(s) + 2H+ ® Ni2+ + H2O Ppt15

Formation of a gas gases exit the reacting solution driving the reaction examples: 2HCl(aq) + Na2CO3(aq)  2NaCl(aq) + H2O(l) + CO2(g) 2HCl(aq) + Na2S(aq)  2NaCl(aq) + H2S(g) 2H+ + 2Cl- + 2Na+ + CO32- ® 2Na+ + 2Cl- + H2CO3 H2O + CO2 2H+ + 2Cl- + 2Na+ + S2- ® 2Na+ + 2Cl- + H2S(g) PS6 Written, problems 7-9 reflect this material Ppt15