Announcements. Exam 1 is on Thursday, September 23 from 7-8:10pm; Conflict exam is from 5:35-6:45pm

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Pierce Hutchinson
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1 Announcements Print worksheet #6 prior to your Tuesday discussion section LON-CAPA assignment 4 is now available Don t forget to bring your Clicker to class EVERY day The points from last week have been uploaded to the online gradebook. Check to make sure your points are shown! Exam 1 is on Thursday, September 23 from 7-8:10pm; Conflict exam is from 5:35-6:45pm

2 Aqueous Reactions Lead(II) nitrate is a solid that can be dissolved in water Lead(II) nitrate is a strong electrolyte, so it dissociates completely into ions when dissolved in water Pb(NO 3 ) 2 (s) + H 2 O (l) Pb 2+ (aq) + 2 NO 3- (aq) Potassium iodide is a solid that can be dissolved in water Potassium iodide is a strong electrolyte, so it dissociates completely into ions when dissolved in water KI (s) + H 2 O (l) K + (aq) + I - (aq)

3 Aqueous Reactions When solutions of lead(ii) nitrate and potassium iodide are mixed together, a yellow solid forms in the solution The yellow solid is known as a precipitate Pb 2+ (aq) + 2 NO 3- (aq) + K + (aq) + I - (aq) What s the identity of the yellow solid? yellow solid + solution Pb(NO 3 ) 2 PbI 2 KNO 3 KI displacement reaction the ions switch partners

4 Solubility rules 1. Most NO 3- salts are soluble 2. Most salts of alkali metals (IA) and NH 4+ are soluble 3. Most Cl -, Br - and I - salts are soluble Exceptions: Ag +, Pb 2+ and Hg 2+ 2 insoluble 4. Most SO 2-4 are soluble Exceptions: Ca 2+, Ba 2+, Pb 2+, Hg 2+ 2 insoluble 5. Most OH - are insoluble Exceptions: IA, Ca 2+, Ba 2+, Sr 2+ soluble 6. Most S 2-, CO 2-3, CrO 2-4, PO 3-4 insoluble Exceptions: IA, NH 4+ soluble

5 Pb 2+ (aq) + 2 NO 3- (aq) + K + (aq) + I - (aq) PbI 2 (s) + K + (aq) + NO 3- (aq) yellow solid + solution 1. Most NO 3- salts are soluble 2. Most IA salts are soluble PbI 2 KNO 3 3. Most Cl -, Br - and I - salts are soluble Exceptions: Ag +, Pb 2+ and Hg 2+ 2 insoluble This equation still needs to be balanced...

6 balance molecular equation Pb(NO 3 ) 2 (aq) + 2KI (aq) PbI 2 (s) + 2KNO 3 (aq) balance ionic equation 1. Most NO 3 2- salts are soluble 2. Most Group I salts are soluble 3. Most Cl -, Br - and I - salts are soluble except Ag +, Pb 2+ and Hg 2+ 2 Pb 2+ (aq)+ 2NO 3- (aq) + 2K + (aq) + 2I - (aq) PbI 2 (s) +K 2 + (aq) + 2NO 3- (aq)

7 The ionic equation contains several ions that appear as both reactants and products these are known as spectator ions Pb 2+ (aq)+ 2NO 3- (aq) + 2K + (aq) + 2I - (aq) PbI 2 (s) + 2K + (aq) + 2NO 3- (aq) A net ionic equation eliminates all the spectator ions: Pb 2+ (aq) + 2I - (aq) PbI 2 (s)

8 Acid/Base reactions HCl dissociates completely H + (aq) Cl - (aq) strong NaOH dissociates completely strong Na + (aq) OH - (aq) acid base molecular eqn HCl(aq)+ NaOH(aq) H 2 O(l) + NaCl(aq) ionic eqn net ionic eqn H + +Cl - + Na + + OH - H 2 O + Na + + Cl - H + + OH - H 2 O

9 Acid/Base reactions HCl dissociates completely H + (aq) Cl - (aq) strong acid Mg(OH) 2 does not dissociate completely weak base Mg(OH) 2 (aq) Mg 2+ (aq) + 2OH - (aq) H + + Cl - + Mg(OH) 2 + Mg OH - H 2 O+ Mg 2+ + Cl - molecular eqn Mg(OH) HCl 2 H 2 O+ MgCl 2 ionic eqn Mg(OH) 2 + 2H + + 2Cl - 2 H 2 O+ Mg 2+ +2Cl - net ionic eqn Mg(OH) 2 (s) +2 H + (aq) 2 H 2 O(l) + Mg 2+ (aq)

10 Acid/Base reactions neutralization reactions produce water from an acid and a base At the equivalence point, [H + ] = [OH - ] mol H + L = mol OH - L What volume of M HCl is needed to neutralize ml of M NaOH? x 10-3 L mol NaOH = 8.75 x 10-3 mol NaOH L 8.75 x 10-3 mol HCl 1 L = L= 87.5 ml HCl mol HCl

11 A 2.2 g sample of an unknown acid, HA, is dissolved in 1.0 L of water. A titration required 25.0 ml of M NaOH to react completely. What is the molecular weight of the unknown? molecular weight = g HA mol HA = mol HA = mol H + = mol OH g HA? mol HA L mol NaOH L = mol OH g HA mol HA = 180 g/mol

12 Enthalpy *The textbook goes into too much detail in sections ΔH = enthalpy change = heat gained/released by a reaction ΔH > 0 means the reaction uses heat as a reactant. The reaction needs the heat to generate the products. (Endothermic) ΔH < 0 means heat is a product of the reaction. Heat is given off during the course of the reaction. (Exothermic) See problems for practice identifying endothermic and exothermic reactions

13 Enthalpy The amount of heat required/released by a reaction can be determined using stoichiometry: CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(l) ΔH = -891 kj The stoichiometry implies that 891 kj of heat are released for every 1 mole of CH 4 reacted... or that 891 kj of heat are released for every 2 moles of H 2 O produced or that 891 kj of heat are released for every 1 mole of CO 2 produced, etc. How much heat is released if 1.00 g of CH 4 reacts with an excess of oxygen? 1.00 g CH 4 1 mol CH kj g CH4 1 mol CH 4 = kj heat See problems for more stoichiometry practice

Solution Chemistry. Chapter 4

Solution Chemistry. Chapter 4 Solution Chemistry Chapter 4 Covalent Molecule Dissolving in Water Ionic Compound Dissolving in Water Electrolytes and Nonelectrolytes Electrolytes/Nonelectrolytes Type Dissociation Electrical Conductivity