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 1 Ppt15

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– 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) K 2 S (aq)  2 K + (aq) + S 2 - (aq) (NH 4 ) 2 CO 3 (aq)  2 NH 4 + (aq) + CO (aq) CaCO 3 (s)  not soluble 3 Ppt15

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Review – How many moles of K + ions are present in 0.25 L of M K 2 CO 3 solution? – K 2 CO 3  2 K + (aq) + CO 3 2- (aq) 0.25 L x mol x 2 mol K + = L 1 mol K 2 CO 3 mol K + mol K 2 CO 3 [M x V = mol] subscript (ratio) [mol A from mol A x B y ] 5 Ppt15

Acids/Bases/Salts – Acids have an ionizable hydrogen, H + eg. HCl (aq) or HC 2 H 3 O 2(aq) can be strong or weak electrolytes 6 Ppt15

– Strong Acids--know these! HCl, HBr, HI, HNO 3, H 2 SO 4, HClO 4 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 ( NH 3 or similar molecular compounds) –NaOH (aq)  Na + (aq) + OH - (aq) –NH 3 (aq) + H 2 O  NH 4 + (aq) + OH - (aq) 7 Ppt15

Molecular vs. Ionic Equations – Three ways to express ionic equations molecular equation--all species expressed as neutral formulas (regardless of whether substance is molecular or not) –HCl (aq) + NaOH (aq)  H 2 O (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)  H 2 O (l) + Na + (aq) + Cl - (aq) –spectator ions: ions that undergo no change 8 Ppt15

NET ionic equation--incl. only species that change (so cross out any that are on both sides [spectators]) – H + (aq) + OH - (aq)  H 2 O (l) Remember, only strong electrolytes (i.e., soluble ionic compounds OR strong acids) are written in ionic form! – Examples H 2 S (aq) + 2NaOH (aq)  2H 2 O (l) + Na 2 S (aq) (molec. eqn) H 2 S (aq) + 2Na + (aq) + 2OH - (aq)  2H 2 O (l) + 2Na + (aq) + S 2- (aq) H 2 S (aq) + 2OH - (aq)  2H 2 O (l) + S 2- (aq) (net ionic eqn) 9 Ppt15

Exchange Reactions General Form ion partner exchange –AX + BY  AY + BX –Pb(NO 3 ) 2(aq) + 2KCl (aq)  PbCl 2(s) + 2KNO 3(aq) Driving Forces formation of an insoluble solid [see precipitate] formation of a weak or non-electrolyte [warms] formation of a gas [see bubbles] 10 Ppt15

Precipitation Reaction formation of an insoluble solid know the solubility guidelines!! examples: –NaCl (aq) + KNO 3(aq)  NaNO 3(aq) + KCl (aq) –AgNO 3(aq) + KCl (aq)  AgCl + KNO 3 Na + + Cl - + K + + NO 3 -  Na + + NO K + + Cl - aq (soluble) Solid (insoluble) Ag + + NO K + + Cl -  AgCl (s) + K + + NO 3 - Ag + (aq) + Cl - (aq)  AgCl (s) 11 Ppt15 ??? NOTHING CHANGED!  “no reaction” (just a bunch of ions swimming around in solution!)

Formation of a weak or non-electrolyte common example is an acid/base reaction--H 2 O forms know/recognize electrolyte vs non-electrolyte examples: HCl (aq) + NaOH (aq)  H 2 O (l) + NaCl (aq) NiO (s) + 2HNO 3(aq)  Ni(NO 3 ) 2(aq) + H 2 O (l) H + + Cl - + Na + + OH -  H 2 O + Cl - + Na + NiO (s) + 2H + + 2NO 3 -  Ni NO H 2 O NiO (s) + 2H +  Ni 2+ + H 2 O 12 Ppt15 H + + OH -   

– Formation of a gas gases exit the reacting solution driving the reaction examples: –2HCl (aq) + Na 2 CO 3(aq)  2NaCl (aq) + H 2 O (l) + CO 2(g) 2HCl (aq) + Na 2 S (aq)  2NaCl (aq) + H 2 S (g) 2H + + 2Cl - + 2Na + + CO 3 2-  2Na + + 2Cl - + H 2 CO 3 H 2 O + CO 2 PS6, problems 8-11 reflect this material 2H + + 2Cl - + 2Na + + S 2-  2Na + + 2Cl - + H 2 S (g) 13 Ppt15