E3 Redox: Transferring electrons. Oxidation-Reduction (Redox)

Transcription

1 E3 Redox: Transferring electrons Session one of two First hour: Discussion (E) 2nd and 3rd hour: Lab (E3, Parts and 2A) Oxidation-Reduction (Redox) Reactions involve electron transfer. Change in charge (oxidation state) of reactants. Example: 2 Na (s) + Cl 2 (g) 2 NaCl (s) Lose of e s = oxidation (Na Na + in NaCl) Gain of e s = reduction (Cl Cl - in NaCl) Redox reaction 2 Na + Cl 2 2 ΝaCl + energy LEO GER DEMO Loss of electrons (LEO) = oxidation Gain of electrons (GER) = reduction

2 REDOX alf Reactions Oxidation Reduction ( > in oxidation state) ( < in oxidation state) 2 ( Na Na + + e - ) ( Cl 2 + 2e - 2Cl - ) OXIDIZING AGENT Gains electrons and is reduced (GER) REDUCING AGENT Loses electrons and is oxidized (LEO) alf reactions always written to show electron GAIN. The final equation reflects the sum of the balanced half reactions so that electrons lost = electrons gained: 2 Na + Cl 2 2 Na Cl - An oxidizing agent brings about the oxidation of another substance. A reducing agent bring about the reduction of another substance. Redox Agents Q. Identify the reducing agents (RA) and oxidizing agents (OA) in the reaction: 2 Na + Cl 2 2 Νa Cl - + energy RA OA OA RA Metals lose electrons Non-metals gain electrons A VIIIA 2 e s IIA IIIA IVA VA VIA VIIA s 2 3 Li 4 Be 5 B 6 C 7 N 8 O 9 F 0 Ne 2s 2s 2 2s 2 2p 2s 2 2p 2 2s 2 2p 3 2s 2 2p 4 2s 2 2p 5 2s 2 2p 6 Na 3s 9 4s 3 7 Rb 5s 5 5 Cs 6s 8 7 7s 6 2 Mg 3 Al 4 Si 5 P S 7 Cl 8 Ar 3s 2 IIIB IVB VB VIB VIIBVIIIB VIIIB IB IIB 3s 2 3p 3s 2 3p 2 3s 2 3p 3 3s 2 3p 4 3s 2 3p 5 3s 2 3p Ca Sc Ti V Cr Mn Fe Co Ni Ga Ge As Se Br r 4s 2 3d 4s 2 3d 2 4s 2 3d 3 4s 2 3d 5 4s 3d 5 4s 2 3d 6 4s 2 3d 7 4s 2 3d 8 4s 2 4s 2 4p 4s 2 4p 2 4s 2 4p 3 4s 2 4p 4 4s 2 4p 5 4s 2 4p 6 3d 0 4s 3d 0 4s Sr 5s 2 Oxidation State versus Family Number Y Zr Nb Mo Tc Ru Rh Pd 4d 5s 2 4d 2 5s 2 4d 3 5s 2 4d 5 5s 4d 5 5s 2 4d 7 5s 4d 8 5s 4d Ag Cd In Sn Sb Te I Xe 4d 0 5s 4d 0 5s 2 5s 2 5p 5s 2 5p 2 5s 2 5p 3 5s 2 5p 4 5s 2 5p 5 5s 2 5p Ba La* f 7 3 Ta 7 4 W 7 5 Re 7 6 Os 7 7 Ir 7 8 Pt 7 9 Au 8 0 g 8 Tl 8 2 Pb 8 3 Bi 8 4 Po 8 5 At 8 6 Rn 6s 2 5d 6s 2 5d 6s 2 5d 6s 2 5d 6s 2 5d 6s 2 5d 6s 2 5d 6s 2 5d 6s 6s 6p 6s 2 6p 2 6s 2 6p 3 6s 2 6p 4 6s 2 6p 5 6s 2 6p d 0 6s 5d 0 6s Element synthesized, Ra Ac # but no official name assigned 7s 2 6d 7s 2 6d 2 7s 2 6d 3 7s 2 6d 4 7s 2 6d 5 7s 2 6d 6 7s 2 6d 7 7s 2 2

3 A 2 IIA Nonmetals gain electrons and reduce (GER) IIIB IVB VB 6 VIB 7 8 VIIB VIIIB 9 0 VIIIB IB 2 IIB + Element synthesized, but no official name assigned 8 VIIIA e IIIA IVA VA VIAVIIA s B C N O F Ne 2s 2 2p 2s 2 2p 2 2s 2 2p Si P 3s 2 3p 2 3s 2 3p As 4s 2 4p 3 2s 2 2p 4 2s 2 2p 5 2s 2 2p 6 6 S 7 Cl 8 Ar 3s 2 3p 4 3s 2 3p 5 3s 2 3p Se 3 5 Br 3 6 r 4s 2 4p 4 4s 2 4p 5 4s 2 4p Te I 5s 2 5p 4 5s 2 5p At 6s 2 6p Xe 5s 2 5p Rn 6s 2 6p 6 + A s 2 IIA 3 4 Li Be 2s 2s 2 2 Na Mg 3s 3s 2 3 IIIB 9 4s 3 7 Rb 5s 5 5 Cs 6s 8 7 7s Family A Metals Q. Maximum charge vs. family#? Q2. Possible oxidation states of Sn? + 3 IIIA V I I A IVA VA VIA Al VIIIB IVB VB VIB VIIB VIIIB IB IIB 3s 2 3p Ca Sc Ti V Cr Mn Fe Co Ni Ga Ge 4s 2 4s 2 3d 4s 2 3d 2 4s 2 3d 3 4s 3d 5 4s 2 3d 5 4s 2 3d 6 4s 2 3d 7 4s 2 3d 8 4s 3d 0 4s 2 3d 0 4s 2 4p 4s 2 4p Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb 5s 2 5s 2 4d 2 5s 2 4d 2 5s 2 4d 3 5s 4d 5 5s 2 3d 5 5s 4d 7 5s 4d 8 4d 0 5s 4d 0 5s 2 4d 0 5s 2 5p 5s 2 5p 2 5s 2 5p Ba L a * f Ta W Re Os Ir Pt Au g Tl Pb Bi Po 6s 2 6s 2 5d 6s 2 5d 2 6s 2 5d 3 6s 2 5d 4 6s 2 4d 5 6s 2 5d 6 5d 7 6s 2 6s 5d 9 6s 5d 0 6s 2 5d 0 6s 2 6p 6s 2 6p 2 6s 2 6p 3 6s 2 6p Element synthesized, Ra Ac # s 2 7s 2 6d 7s 2 6d 2 7s 2 7d 3 7s 2 6d 4 7s 2 3d 5 6s 2 6d 6 6d 7 7s 2 but no official name assigned 8 VIIIA Ions with multiple oxidation states Q. Sn (Group IVA) has oxidation states of zero, plus two, and plus four. Write half reactions depicting: Reduction of Sn 2+ ion: Sn e- Sn Oxidation of Sn 2+ ion: Sn 2+ Sn e- Sn 2+ can act as an oxidizing or reducing agent in redox reactions A 2 3 s IIA IIIA 4 IVA 5 VA 6 VIA 3 4 Li Be 2s 2s Na Mg Al 3s 3s 2 IIIB IVB VB VIB VIIB VIIIB " VIIIB IB IIB 3s 2 3p 9 4s 2 0 Ca 4s 2 Transition Metals Q. Maximum oxidation state vs. family #? 2 Sc 4s 2 3d 2 2 Ti 2 3 V 2 4 Cr 2 5 Mn 2 6 Fe 2 7 Co 2 8 Ni 2 9 4s 2 3d 2 4s 2 3d 3 4s 3d 5 4s 2 3d 5 4s 2 3d 6 4s 2 3d 7 4s 2 3d 8 4s 3d Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag 5s 5s 2 5s 2 4d 2 5s 2 4d 2 5s 2 4d 3 5s 4d 5 5s 2 3d 5 5s 4d 7 5s 4d 8 4d 0 5s 4d Cs Ba La* f Ta W Re Os Ir Pt Au 6s 6s 2 6s 2 5d 6s 2 5d 2 6s 2 5d 3 6s 2 5d 4 6s 2 4d 5 6s 2 5d 6 5d 7 6s 2 6s 5d 9 6s 5d Ra Ac # s 7s 2 7s 2 6d 7s 2 6d 2 7s 2 7d 3 7s 2 6d 4 7s 2 3d 5 6s 2 6d 6 6d 7 7s s 2 3d 0 3 Ga 4s 2 4p Cd In 5s 2 4d 0 5s 2 5p g Tl 6s 2 5d 0 6s 2 6p + Element synthesized, but no official name assigned 3 2 Ge 4s 2 4p Sn Sb 5s 2 5p 2 5s 2 5p Pb 8 3 Bi 8 4 Po 6s 2 6p 2 6s 2 6p 3 6s 2 6p 4 7 VIIA 8 VIIIA 3

4 Strength of Redox Agents Example: 2 Na + Cl 2 2 Νa Cl - RA OA OA RA The reactants are the stronger RA and OA and react spontaneously The non-reactive products are the weaker OA and RA. Redox agent strength Q. Rank the strength of the reducing/oxidizing agents in the reaction below: 2 Sb + 3 Cl 2 2 Sb Cl - RA OA OA RA RA strength: Sb > Cl - OA strength: Cl 2 > Sb 3+ RA: Na > Cl - OA: Cl 2 > Na + Reaction and Redox Strength If RA: > Ag OA: Ag + > 2+ Reactions and Redox Strength The stronger RA and OA react: Reactants (s) + Ag + (aq) reaction The weaker RA and OA do NOT react: (s) + Ag + (aq)? Ag(s) + 2+ (aq)? DEMO Ag(s) + 2+ (aq) no reaction 4

5 Part I B. Predicting Metal Reactivity. Determine the reducing agent (RA) strength of four team assigned metals where the metal ions of all four metals are available and only three of the four metals are available for experimental tests. Experiment Design and Data Analysis Example You need to determine the reducing agent strength of,, and Mg. Problem Available: Solutions of 2+, 2+, and Mg 2+. and only (i.e., Mg is unavailable) Experiment Design for Part B. Create a table for recording data (pre-lab). Mg Mg 2+ Reducing agent species (metals) on one side and oxidizing agents species (metal ions) on other side. Experiment Design and Data Analysis Test available metal and metal ion combinations Record observations Example: (s) + 2+ (aq) reaction 5

6 Check data. Does it make sense? Data Analysis # rxns # rxns. Rxn No Reaction Rxn No No 0 # rxns. # rxns. 0 These results don t make sense This data makes sense: The stronger RA and OA show more reactions RA and OA strength are inverse: Only one combination of metal and metal ion should react spontaneously -- the stronger RA and OA RA: > OA: 2+ > 2+ Reducing Agent Strength of Mg,, and? Part I A. Metal reactions with water. Q. Complete the table below No Rxn. No No Mg Rxn Rxn Mg 2+ No No No Rank the reducing agent strength of the metals Na,, Mg, and Ca from experimental observations. Correlate the results with the position of the metal in the periodic table. Q2. Comparative RA strength of the metals? RA strength: Mg > > 6

7 Experimental Comparison of Ca and Mg Metal + Water metal hydroxide + 2 (g) RA OA OA RA Example: Mg (s) + 2O (l) Mg(O) 2(s) + 2(g) Reactivity of and Na Experimental determination of the reactivity of and Na compared to Ca and Mg. DEMO DEMO RA: Ca > Mg Experimental Comparison of, Na, Ca, and Mg Na skitters around the skitters around the water surface water surface and ignites RA: > Na > Ca > Mg RA and OA Predictions from Electronegativity values = Electron pulling power of an atom when part of a bond Electronegativity of the elements IA IIA IIIB IVB VB VIB VIIB VIIIB IB IIB IIIA IVA VA VIA VIIA 2. Li.0 Be B C 2.5 N 3.0 O 3.5 F 4.0 Na Mg Al Si P S Cl Ca.0 Sc.3 Ti V Cr Mn Fe Co Ni Ga Ge As Se Br 2.8 Rb Sr.0 Y.2 Zr.4 Nb Mo Tc Ru Rh Pd Ag Cd.7 In.7 Sn Sb Te 2. I 2.5 Cs Ba La f Ta W Re Os Ir Pt Au g Tl Pb Bi Po At -Lu.3.7 Ra Ac. Th.3 Pa U.7 Np- No.3 = Metalloids = Nonmetals = Metals 7

8 IA IIA IIIB IVB VB VIB VIIB VIIIB IB IIB IIIA IVA VA VIA VIIA 2. Li Be B C N O F Na Mg Al Si P S Cl Ca.0 Sc.3 Ti V Cr Mn Fe Co Ni Ga Ge As Se Br 2.8 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Cs Q. Predict the RA strength of compared to Na, Mg, and Ca based on position and electronegativity values..0 Ba Ra.2.4 La f -Lu.3 Ac Th..3 Ta Pa W.7 U.7 Re Os Np- No.3 > > > Ir Pt Au.7 g.7 Tl Pb Bi 2. Po > Na > Ca > Mg 2.5 At IA IIA IIIB IVB VB VIB VIIB VIIIB IB IIB IIIA IVA VA VIA VIIA 2. Li Be B C N O F Na Mg Al Si P S Cl Ca.0 Sc.3 Ti V Cr Mn Fe Co Ni Ga Ge As Se Br 2.8 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Cs Q. Where are the best reducing and oxidizing agents located?.0 Ba Ra.2.4 La f -Lu.3 Ac Th..3 Ta Pa W.7 U.7 Re Os Np- No.3 Ir Pt Au.7 g.7 Tl Pb Bi 2. Po Caution: Attraction of metal or nonmetal ion for electrons in a bond is different from its metal or nonmetal element. 2.5 At Questions? Contact 8