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Exam 2 Wednesday 4/4 Homework 9 posted and due today

Exam 2 Wednesday 4/4 Homework 9 posted and due today. Oxidation # RULES SUMMARIZED. 1) PURE UNCHARGED ELEMENTS HAVE 0 OXIDATION #. 2) OXIDATION # OF A CHARGED ATOM IS THE CHARGE ITSELF. F (AND USUALLY THE OTHER HALOGENS) ARE -1 IN BINARY AND LARGER COMPOUNDS.

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Exam 2 Wednesday 4/4 Homework 9 posted and due today

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  1. Exam 2 Wednesday 4/4 Homework 9 posted and due today

  2. Oxidation # RULES SUMMARIZED 1) PURE UNCHARGED ELEMENTS HAVE 0 OXIDATION # 2) OXIDATION # OF A CHARGED ATOM IS THE CHARGE ITSELF • F (AND USUALLY THE OTHER HALOGENS) ARE • -1 IN BINARY AND LARGER COMPOUNDS 4) O IS -2 EXCEPT IN PEROXIDES (X-OO-Y) WHERE IT IS -1 5) H IS +1 FOR COVALENT COMPOUNDS (AND MOST IONIC ONES TOO)

  3. PRACTICE ASSIGNING OXIDATION # Provide oxidation # for all elements below N2 O2 H2O Fe2O3 H2SO4 N=0 O=0 H=+1 O= -2 Fe=+3 O= -2 H= +1 O= -2 S=+6

  4. PRACTICE ASSIGNING OXIDATION #(cont.) 0 +1-1 +2 -1 0 Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g) Zn Which element oxidized ? w/demo 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 ? w/demo Cu Which element reduced ?

  5. What are the oxidation # for H, Mn and O in HMnO4 • H=+1, Mn=+3, O=-1 • H=+1, Mn =+7, O=-2 • H=0, Mn=8, O =-2 • H=-1, Mn = 9, O=-2

  6. What is oxidized and reduced in the reaction: PbO + COPb+CO2 • O reduced, Pb oxidized • C reduced, Pb oxidized • Pb reduced, O oxidized • Pb reduced, C oxidized

  7. In the reaction: CH4+2O2 CO2+2H2Othe oxidation # for reactant C vs. product C and reactant O vs. product O are: C ; O • +4 vs. -4; 0 vs. +2 • 0vs. +4; -2 vs. +2 • -4vs. +4; 0 vs. +2 • -4 vs.+4; 0 vs. -2

  8. What is oxidized and reduced in the reaction: CH4 +2O2CO2 +2H2O • C oxidized, O reduced • H oxidized, C reduced • C oxidized, H reduced • O oxidized. C reduced

  9. Exam 2 • Moles level 2 (Body parts problem) lectures 13,14 • Moles level 2b (empiric formula) lecture 15 • Moles level 2b (combustion) lecture 15,16 • Moles level 3 (balancing &stoichiometry) lectures 16,17,18 • Moles level 3 (limiting reagents) lectures 18,19,20 • Moles level 3 % yield lectures 20,21 • 7. Classical Reactions (Metathesis, acid-base, redox) lectures 22-24 • See also: homework #5-9. Examples of 1-6 below 75% 25%

  10. How many molecules of C6H12O6 are present in a sample containing 32 g of O (at. wt=16 g/mol)? 1 1 mol count=6*1023 (1. moles level 2- body parts) • 12*1023 • 5*1024 • 3.3*1023 • 2.0*1023

  11. Compound X is composed of 39.34 wt % C, 8.20 wt% H and 52.56 wt% O. What is compound X’s empiric formula ? (2. % composition empiric) • C4H8O5 • CH2O • C2H5O2 • CH3O

  12. A hydrocarbon,CxHy burns to form 22 g CO2 and 18 g H2O. What is the empiric formula of CxHy? (3a. Combustion) • CH • CH2 • CH3 • CH4 • None of above

  13. A 3 g sample of a copper oxide is heated to drive off oxygen. On cooling 2.666 g of pure Cu remains. What is the copper oxide’s empiric formula ? (3b. Combustion) • CuO2 • Cu2O • CuO • CuO3

  14. equation balancing practice (4a: balancing) 4 1 __H3PO3 ___H3PO4 + ___PH3 3 Helpful hint: first balance elements that appear in a single compound on both reactant and product sides.

  15. C3H8 + 5O2--------3CO2 + 4H2O (BOOM) 44 32 44 18 g/mol e) count wt: How many grams of O2are needed to form 9*1022 molecules of H2O ? count wt (4b. Stoichiometry) • 1.0 g • 2.0 g • 1.5 g • 6.0 g

  16. 2C8H18 + 25O2 -------- 16CO2 + 18H2O MW 114 g/mol 32 g/mol 44 g/mol 18 g/mol w(g) 3.24 1.136?? g Given 3.24 g C8H18 and 1.136 g O2, how many grams of CO2form ? (5. Limiting yield) • 10.0 g • 1.0 g • 0.11 g • 1.56 g

  17. MW 16 32 18 CH4 + 2O2 CO2 + 2H2OA 1 g sample of methane (CH4) is burned in excess O2 according to the equation above. You collect 1.125 g of H2O. What is your % yield ?(6. % yield) • 50% • 89 % • 25 % • 100% • I have no idea

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