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3.1 Reaction Stoichiometry , Limiting Reagent and % Yields (5 pts each/20 points total)

EXAM MONDAY 25 NOVEMBER . All material from 23 October Powerpoints 23-36 Mini quizzes 17-23 + lab questions on: Titration Metathesis reactions Gas laws. 3.1 Reaction Stoichiometry , Limiting Reagent and % Yields (5 pts each/20 points total).

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3.1 Reaction Stoichiometry , Limiting Reagent and % Yields (5 pts each/20 points total)

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  1. EXAM MONDAY 25NOVEMBER • All material from 23 October • Powerpoints 23-36 • Mini quizzes 17-23 + lab questions on: • Titration • Metathesis reactions • Gas laws 3.1 Reaction Stoichiometry, Limiting Reagent and % Yields (5 pts each/20 points total) a) How many grams of water are formed in the reaction below when 1.4074 g of C8H18 are burned with excess O2 in the balanced reaction below ? (Must show work for credit) Molecular mass 114 32 44 18 g/mol 2C8H18 + 25 O2 16CO2+ 18H2O b) Using the same balanced reaction above, predict the grams of CO2 expected if 3.409 g of O2 and 3.8863 g C8H18 are burned together. (Must show work for credit) c) Using the same balanced reaction above, compute the % yield for the reaction if 1.14 g of C8H18 in excess O2 yields 0.810 g H2O. (Must show work for credit) 3.2. Ions and Ionic Compound Prediction (14 pts total) Ionic radii ________ in size down a column The most likely ionic compound formed from K and P is:

  2. 3.3 Extended Lewis Structures , Formal Charges and VSEPR Shapes (18 pts total) Draw the best Lewis structure for the compounds below. Make sure to show all lone pairs and indicate any formal charges. (Remember that the best Lewis structure sometimes requires breaking the octet rule to minimize formal charge.) SO3 PO43- What are the shapes of the above compounds ? 3.4. Metathesis Reactions (10 Pts) a) Write the complete balanced molecular, complete ionic and net ionic equation for the reaction of silver nitrate (AgNO3) with calcium chloride (CaCl2) given that both are soluble in water and form an insoluble silver chloride precipitate. b) What are three characteristics of metathesis reactions ? 3.5 Acid-Base Reactions and models (~15 pts) Which are not Arrhenius bases, but can be Bronsted bases in the list below: CO32-HBrCl- OH‑ NH4+ Identify the base (B), acid(A), conjugate acid (CA) and conjugate base (CB) below: NH3 + HBr NH4+ + Br- 2

  3. 3.6 Titration problem (4 pts) Given a standard acid with Ca= 0.25 M, what is the concentration of an unknown base if 25.0 mL of the acid requires 20.00 mL of base to reach equivalence ? 3.7 Ideal Gas question (4 pts) You run the reaction: 2Al(s) + 6HCl(aq)  3H2(g) + 2AlCl3(aq) using 0.17 g of Al (at. wt. = 27.0 g/mol). This produces, according to the Ideal Gas equation, 9.349*10-3 mol H2. a)How many moles of H2 should you get from the reaction if it runs to completion ? b) What is your % EDA to the nearest 0.1% ? 3.8 Redox basics (10 pts) Oxidation means____ What is the oxidation # of Fe in Fe2O3 ? 3.9 Multiple choice and T/F (5 pts) The octet rule is always obeyed T F Who is the Swedish chemist ? Lewis Bronsted Arrhenius

  4. Answers to foregoing exam 3 snapshot examples are posted at course website under exams and quizzes…hit the books, kids !

  5. How to know if a reaction is a `redox’ reaction: assign OXIDATION NUMBERS RULES: (SEE PAGE 460 TABLE 10.2) • PURE UNCHARGED ELEMENTS HAVE 0 OXIDATION # • OXIDATION # OF A CHARGED ATOM IS THE CHARGE ITSELF • F (AND USUALLY THE OTHER HALOGENS) IS -1 • O IS -2 EXCEPT IN PEROXIDES (X-OO-Y) WHERE IT IS -1 • H IS +1 FOR COVALENT COMPOUNDS (AND MOST IONIC ONES TOO)

  6. More PRACTICE ASSIGNING OXIDATION # Al3+ H-O-O-H MnO4-1 Cr2O72- UF6 3+ O=-1 H=+1 Mn=+7 O= -2 Cr=+6 O= -2 U= +6 F= -1

  7. PRACTICE ASSIGNING OXIDATION # in Reactions 0 +1-1 +2 -1 0 Mg(s) + 2HCl(aq)  MgCl2(aq) + H2(g) Mg Which element oxidized ? Which element reduced ? H 0 +2 +6 -2 +3 +6 -2 0 2Al(s) + 3CuSO4(aq) Al2(SO4)3(aq) + 3 Cu(s) Al Which element oxidized ? Cu Which element reduced ?

  8. Characteristics of redox reactions • Heat and light common • Reactions are often spectacular (way, way better than acid-base) • Elemental electronic balance altered (of course) • Often accompanied by major decomposition or combination

  9. SPECTACULAR REDOX REACTION BEHAVIOR 1) Thermite reaction 1)assign oxidation # (U-Do-it) 0+3 -2 0 +3 -2 2Alo(s) + Fe2O3(s)2Fe0 (liq)+Al2O3(s) 2) Who does what? (U-pick-it) Al Which element oxidized ? Which element reduced ? Fe 3)let’s see the reaction in the `flesh’

  10. SPECTACULAR REDOX REACTION BEHAVIOR (continued) Example 2: Combustion (U-Do-it) 1) Assign Oxidation # -4 +1 0 +4 -2 +1 -2 CH4 +2O2 CO2 +2H2O 2) Who does what? (U-pick-it) C Which element oxidized ? Which element reduced ? O 3) BURN BABY, BURN

  11. SPECTACULAR REDOX REACTION BEHAVIOR (continued) Example 3: Combination redox 1) Assign Oxidation # (U-do-it) 0 0 +1 -1 : 2Na + Cl2 NaCl (table salt) 2) Who does what? (U-pick-it) Which element oxidized ? Which element reduced ? 3) Let’s see it

  12. SPECTACULAR REDOX REACTION BEHAVIOR (continued) 4) Decomposition redox: aka The DEATH TO SKITTLES REACTION And now, the dangerous, scary In-class demo… 0 +1 -2 +1 +7 -2 +1 -2 +4 -2 +1 -1 C12H22O11 + 8KClO311H2O + 12CO2 + 8KCl Red Ox

  13. One other unique and highly useful feature of redox reactions… The oxidation and reduction can be separated in space and you can still run the reaction as a `cell’ or ‘battery’

  14. Example: Cu-Mg cell The complete redox reaction Gains 2e- Cu2++ Mgo Cuo +Mg2+ Loses 2e- Reduction half reaction: Cu2+ +2e- Cuo cathode Oxidation half reaction: MgoMg2+ +2e- anode Cu2++ Mgo Cuo +Mg2+

  15. The experimental set-up of (Mg|Mg2+ ||Cu2+ |Cu) cell LOAD Electron flow out of anode Mg0Mg2+ +2e- NaCl bridge Cl- Na+ anode cathode Cu2+ +2e-Cuo Oxidation Reduction

  16. Traditional demo • Potato clock

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