1 Ionic Equations Ionic compounds and acids dissociate (separate) when dissolved in water (Aqueous) Examples: CuSO 4 (aq)  Cu 2+ (aq) + SO 4 2- (aq) MgSO 4 (aq)  Mg 2+ (aq) + SO 4 2- (aq) CuSO 4 (aq) or MgSO 4 (aq): Ions written together in formula, actually separated when dissolved in water. Most molecular compounds Don’t separate when (aq) H 2 O Ex: glucoseC 6 H 12 O 6 (s)  C 6 H 12 O 6 (aq)

2 In single replacement reactions: Ex: Zn (s) + CuSO 4 (aq)  Cu (s) + ZnSO 4 (aq) Mg (s) + CuSO 4(aq)  Cu (s) + MgSO 4(aq) ↓ ↓ ↓ ↓ Zn (s) + Cu 2+ (aq) + SO 4 2- (aq)  Cu (s) + Zn 2+ (aq) + SO 4 2- (aq) Note: sulfate SO 4 2- is aqueous before and after reaction (not changing): called a spectator ion The Net equation: Zn (s) + Cu 2+ (aq)  Cu (s) + Zn 2+ (aq)

3 Net ionic equation: Includes only atoms and ions involved in reaction (Spectator ions removed) Mg 0 (s) + Cu 2+ __ (aq)  Cu 0 (s) + Mg 2+ __ (aq) Reactants: Mg o atoms and Cu 2+ ions Products: Cu 0 atoms and Mg 2+ ions Notice Neutral Mg atoms lose electrons forming Mg 2+ ions While Cu 2+ ions gain electrons forming neutral Cu atoms. Magnesium is giving up electrons to Cu 2+

4 Short cut: Ex: F 2 (g) + 2 NaCl (aq)  Cl 2 (g) + 2 NaF (aq) Split aqueous compounds: F 2 (g) + 2 Na|Cl (aq)  Cl 2 (g) + 2 Na|F (aq) Cancel out aqueous ions (spectators) from both sides: Na + (aq) F 2 (g) + 2 NaCl (aq)  Cl 2 (g) + 2 NaF (aq) Rewrite without spectators but add charges to leftover ions: F 2 (g) + 2 _Cl -1 (aq)  Cl 2 (g) + 2 _F -1 (aq) F 2 (g) + 2 Cl - (aq)  Cl 2 (g) + 2 F - (aq)

5 Double replacement reactions Ex 1: K 2 CrO 4(aq) + Pb(NO 3 ) 2(aq)  PbCrO 4 (s) + 2 KNO 3(aq) Split (aq): K 2 |CrO 4(aq) + Pb|(NO 3 ) 2(aq)  PbCrO 4 (s) + 2 K|NO 3(aq) Identify spectators: K + and NO 3 - ions Cancel spectators and add charges to separated ions: ___CrO 4 2- (aq) + Pb 2+ ___ (aq)  PbCrO 4 (s) + ____ ____ Pb 2+ (aq) + CrO 4 2- (aq)  PbCrO 4 (s)

6 Ex 2: Acids (molecular) split into ions like ionic compounds HCl (aq) + NaOH (aq)  H 2 O (l) + NaCl (aq) Split aqueous and cancel spectators, add charges: H|Cl (aq) + Na|OH (aq)  H 2 O (l) + Na|Cl (aq) spectators? Cl - ions and Na + ions Net ionic equation for neutralization: H + (aq) + OH - (aq)  H 2 O (l) 1-1+

7 Test your learning Write the balanced equation for the reaction between aqueous barium hydroxide and hydrochloric acid (aqueous hydrogen chloride). Write the word equation: Write the skeleton equation then balance: Write complete and net ionic equation: Predict the products (what type of reaction is it?) :

8 Equation Math (Stoichiometry) Coefficients in chemical equations represent a # (mole) ratio Ex: Haber process: reaction of nitrogen gas with hydrogen gas to form ammonia. N 2 + H 2  NH 3 1 N H 2  2 NH 3 1 molecule N molecules H 2  2 molecules NH 3 1 mole N moles H 2  2 moles NH 3 1 : 3 : 2 mole ratio If 1 mole of N 2 reacts with 3 moles of H 2, 2 moles of NH 3 are produced.

9 1 N H 2  2 NH 3 If 2 mol N 2 react  ? Mol NH 3 produced? 2 mol N 2 4 mol NH N H 2  2 NH 3 ? mol N 2 ? mol H 2 ? 0.5 mol N mol H N H 2  2 NH 3 4 mol H 2  ? Mol NH 3 ? 4 x 2/3 = 2.67 mol NH 3

10 Mole – mole problems: Ex 1: ammonia forms according to the equation N H 2  2 NH 3 How many moles of ammonia are formed from the reaction of 2.5 moles of hydrogen gas? 2.5 mol  ? mol Ratio: 3 mol H 2 = 2 mol NH mol H 2 X mol NH 3 mol H 2 = 1.7 mol NH 3 2 3

11 Ex 2:N H 2  2 NH 3 How many moles of hydrogen is required to react with 3.5 moles of nitrogen? How many moles of ammonia is produced? 3.5 mol ? mol 3.5 mol N 2 x3 mol H 2 1 mol N 2 = 10.5 mol H 2 ? mol 3.5 mol N 2 x 2 mol NH 3 1 mol N 2 1 mol N 2 = 7 mol NH 3

12 Mass-mass problems: Convert mass to moles in order to use coefficient ratios Ex 3 How many grams of oxygen is produced by the decomposition of 100 grams of water? 2 H 2 O  2 H 2 + O g? g  ?  Can’t go from grams to grams ? Moles H 2 O? Moles O 2

13 Mass-mass problems: Convert mass to moles in order to use coefficient ratios Ex 3 How many grams of oxygen is produced by the decomposition of 100 grams of water? 2 H 2 O  2 H 2 + O g H 2 OX 1 mol H 2 O 18 g X 1 mol O 2 2 mol H 2 O X 32 g 1 mol O 2 = 89 g O 2

14 Gas Volume problems Ex 4 What volume of oxygen is released from the decomposition of 50 g water? 2 H 2 O  2 H 2 + O 2 50 grams? Liters Can’t go from grams to liters 50 gramsX 1 mol H 2 O 18 g X 1 mol O 2 2 mol H 2 O X 22.4 liters 1 mol O 2

15 A short-cut for mole-mole problems How many moles of NH 3 are produced, when 10 moles of H 2 react? N H 2  2 NH 3 _X mol_ = _10 mol_ 3X = (2)(10)X = 6.7 moles NH 3 _10 _ = _X_ 3 2