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Redox, Electrochemistry, and Radioactivity --Whew. Redox • A reduction is a gain of electrons, an oxidation is a loss of electrons • A reduction is always conjoined with an oxidation (electrons are neither created nor destroyed, charges must balance) • Remember “OILRIG” OILRIG Oxidation is loss of electrons Reduction is gain of electrons Or… LEO says GER Loss of electrons is oxidation Gain of electrons is reduction For example: +2 +2 Cu (aq)+Fe(s)Fe (aq)+Cu(s) (right?) For example: +2 +2 Cu (aq)+Fe(s)Fe (aq)+Cu(s) (right?) • The iron loses custody of its electrons to form the +2 ion. • The iron is oxidized to an iron (II) ion, the copper ion is reduced to copper atom For example: 2H2 +O22H2O (right?) For example: 2H2 +O22H2O (right?) • The hydrogen loses (partial) custody of its electrons when it makes the polar covalent bond. For example: 2H2 +O22H2O (right?) • The hydrogen loses custody of its electrons when it makes the polar covalent bond. • The hydrogen is oxidized, the oxygen is reduced In general… • If an atom forms a (-) ion, it has been reduced—happens to nonmetals • If an atom forms a (+) ion, it has been oxidized—happens to metals • Combining with O2 (or F2 or Cl2) is an oxidation—the O2 (or F2 or Cl2) is reduced In general… • If an atom forms a (-) ion, it has been reduced—happens to nonmetals A (-) ion forming an element is an oxidation • If an atom forms a (+) ion, it has been oxidized—happens to metals A (+) ion forming an element is a reduction • Combining with O2 (or F2 or Cl2) is an oxidation—the O2 (or F2 or Cl2) is reduced Mark the oxidation and reduction 2H2 +O22H2O Mark the oxidation and reduction reduction 2H2 +O22H2O oxidation Mark the oxidation and reduction reduction 2H2 +O22H2O Hydrogen is the reducing agent oxidation Oxygen is the oxidizing agent Mark the oxidation and reduction reduction 2H2 +O22H2O Hydrogen is the reducing agent (it gets oxidized) oxidation Oxygen is the oxidizing agent (it gets reduced) Mark the oxidation and reduction (include the agents and what happens to each) Cu+2(aq)+Fe(s)Fe+2(aq)+Cu(s) Which gets oxidized? Which gets reduced? 6Li + N2 2 Li3N O2 + N2 2 NO 16K + S8 8 K2S S8 + 16F2 8 SF4 Br2 + 2NaI I2 + 2 NaBr 2NaCl 2 Na + Cl2 H2 + Cl2 2 HCl Which gets oxidized? Which gets reduced? 6Li + N2 2 Li3N O2 + N2 2 NO 16K + S8 8 K2S S8 + 16F2 8 SF4 Br2 + 2NaI I2 + 2 NaBr 2NaCl 2 Na + Cl2 H2 + Cl2 2 HCl Which gets oxidized? Which gets reduced? 6Li + N2 2 Li3N O2 + N2 2 NO 16K + S8 8 K2S S8 + 16F2 8 SF4 Br2 + 2NaI I2 + 2 NaBr 2NaCl 2 Na + Cl2 H2 + Cl2 2 HCl What if it’s not so easy? 2NH3+NaOClN2H4+NaCl+H2O Oxidation Numbers Summary of Oxidation State Rules 1) Free element Oxidation State = 0 2) Compound total Oxidation State = 0 3) Ion Oxidation State = its charge 4) Oxygen Oxidation State = -2 (except peroxides =-1 each) 5) Hydrogen Oxidation State = +1 (except hydrides =-1) What is the oxidation number? of each atom in sodium hypochlorite NaOCl What is the oxidation number? Sodium hypochlorite is a compound, all together oxidation numbers = 0 NaOCl What is the oxidation number? The Na+ ion has +1 charge +1 NaOCl . Oxidation number = +1 What is the oxidation number? +1 NaOCl . The OCl- ion has -1 charge Oxidation numbers add up to -1 What is the oxidation number? +1 -2 . NaOCl The O atom: -2 charge Oxidation numbers add up to -1 What is the oxidation number? +1 -2 +1 NaOCl . So the Cl must be +1! What is the oxidation number? NaCl KMnO4 diamond CO2 CO KCN Na4Fe(CN) 6 Fe2O3 Fe3O4 ClO4- ClO3ClO2ClOClCl2 P2O5 P4O6 H3PO4 Mg3N2 MgH2 NH3 N 2H 4 NH4+ Au NO3NO2NO2 NO N 2O Na2O2 Now, it’s easy 2NH3+NaOClN2H4+NaCl+H2O Now, it’s easy -3 +1 +1 -2 +1 -2 +1 +1 -1 +1 -2 2NH3+NaOClN2H4+NaCl+H2O Now, it’s easy reduction -3 +1 +1 -2 +1 -2 +1 +1 -1 +1 -2 2NH3+NaOClN2H4+NaCl+H2O oxidation Does a redox reaction occur? • Look for an oxidizing agent and a reducing agent. • If there is one of each, then ask, “Can this oxidizing agent oxidize this reducing agent” Answer by comparing reduction potentials. (page 688) • (Don’t memorize a rule, compare the values to a reaction you know will occur) Does a redox reaction occur? If you combine… • Na+ and Fe+3? • Cl- and Ag? • Cu and K+ ? • Pb+2 and I- ? • Fe+2 and Mg? Does a redox reaction occur? If you combine… • Na+ and Fe+3? • Cl- and Ag? • Cu and K+ ? • Pb+2 and I- ? • Fe+2 and Mg? Can be reduced, but not oxidized further Does a redox reaction occur? If you combine… • Na+ and Fe+3?—No. There is no reducer. • Cl- and Ag? • Cu and K+ ? • Pb+2 and I- ? • Fe+2 and Mg? Does a redox reaction occur? If you combine… • Na+ and Fe+3?—No. There is no reducer. • Cl- and Ag?—No. There is no oxidizer. • Cu and K+ ?—No. This oxidizer can’t do it • Pb+2 and I- ?—No, but it will precipitate. • Fe+2 and Mg?—Yes. Fe+2 + Mg Fe and Mg+2 Redox—half reactions • Balance the atoms • Add H2O and H+ to balance oxygen and hydrogen • Rectify the electrons, add and cancel • Check that charges are balanced • (Add OH- if the reaction is specified as in a basic solution) Try it. • S2O3-2 + NO3- • H2O2 + Fe+2 • Cr2O7-2 + I- • MnO4- + C2H5OH Try it. • S2O3-2 + NO3- SO4-2 + NO • H2O2 + Fe+2 H2O + Fe+3 • Cr2O7-2 + I- Cr+3 + I2 • MnO4- + C2H5OH Mn+2 + CO2 + H2O Try it. 3x(S2O3-2 + 5H2O 2 SO4-2 +10H + + 8 e-) 8x(NO3- +4H + + 3 e- NO + 2 H2O) 3S2O3-2 + 15H2O 6 SO4-2 +30H + + 24 e-) 8NO3- +32H + + 24 e- 8NO + 16H2O) 3S2O3-2+8NO3-+2H+6SO4-2 +8NO+H2O Reduction potentials • -- Measured as compared to the reduction of 2H+ + 2e- H2. (0.00V) • Half reactions that can accomplish this have (-) reduction potentials • Half reactions that force the reverse have (+) reduction potentials Reduction potentials • Specifically: Magnesium reduces H+ • 2H+ + Mg Mg+2 + H2 which implies that Mg+2 + 2 e- Mg has a Eo<0 • While bromine oxidizes hydrogen gas • H2 + Br2 2H+ +2Br - which implies that; Br2 + 2 e- 2Br – has a Eo>0 Electrochemical Cells • When half reactions are separated, and the electrons are connected in a circuit. • A salt bridge is needed to allow charges to migrate to offset the motion of electrons • Cathode=reduction • An electrode carries electrons to or from a half reaction Shorthand notation • The Danielle Cell, using copper and zinc, Zn|Zn+2||Cu+2|Cu …makes 1.1 V Zn|Zn+2||Cu+2|Cu (or, in general) product reactant Anode of of cathode oxidation reduction If non-metals are used… Pt|H2|H2O||O2|H2O|Pt • The (non-reactive) metal electrode is noted outside the bars Standard cell potentials • Eo=Ered-Eox Be able to: • Sketch a cell (include salt bridge and circuit) • Label anode and cathode • Write the half reactions, complete reaction • Calculate Eo, show direction of electron flow • Describe the oxidation and reduction— with mass changes, observations. • Read and write the shorthand notation Electrolytic Cells • Applying an external voltage will allow a non-spontaneous reaction to occur. 2H2O2H2+O2 is not spontaneous (Right?) If you apply a voltage to water (with some electrolyte added to carry a charge), it will decompose (or electrolyse) Nuclear Chemistry • --breaks the rules that one atom cannot be converted to another. Chemistry is the dance of the electrons—nuclear reactions change the nuclei of atoms • --charge and mass are still conserved. Nuclide Notation • A nuclide is a nucleus or atom of a specific isotope of an element 39 19 K • This is potassium-39. It has 19 protons (atomic number = 19), making it potassium, and 20 neutrons, making a mass number of 39 How many p, n, e- in each? What is the mass number and atomic number? 3 1 59 26 H +3 Fe 36 17 Cl 90 38 +2 Sr 131 53 228 90 I Th Natural decays • a—the loss of a particle from a nuclide --The a particle is composed of 2p and 2n, the 4He nucleus --decreases the mass by 4 and the atomic number by 2 • b—emission of an electron (b particle) from the nucleus by the conversion of a n p + e--the electron is the b particle --increases the atomic number by 1, does not affect mass Write the reaction • • • • • • Argon-39 undergoes a b decay Thorium-228 undergoes an a decay An a decay forms lead-204 A b decay forms nitrogen-14 A natural decay forms Sc-45 from Ca-45 A natural decay forms Ac-227 from Pa-231 Notice what they do • A b decay lowers the n/p ratio in small nuclei, or when the ratio is too large. • An a decay lowers the total size, and raises the n/p in large nuclides, or when the ratio is too small. What is “too large” or “too small”? What is “too large” or “too small”? What is “too large” or “too small”? b decay a decay What is “too large” or “too small”? What is “too large” or “too small”? n:p = 2:1 n:p = 1:1 This just in. • Researchers report the first creation of the long-lived nucleus hassium-270, a "doubly magic" combination of 108 protons and 162 neutrons. Its long lifetime of 22 seconds supports the theory of an "island of stability" for the heaviest elements. (J Dvorak et al. 2006 Phys. Rev. Lett. 97, 242501) Nuclear reactions • Many nuclear reactions involve colliding nuclei or smaller particles at some significant fraction of the speed of light, • --find the missing particle by balancing mass and charge. Particles might include… • • • • • • p n e- (AKA b) d a g (OK, it’s not a particle, but it’s often written in) In comparison • Physical changes: joules/mole range • Chemical changes: kilojoules/mole range • Nuclear changes: megajoules/mole range Fission vs Fusion • Fission=breaking up large nuclei— --natural radioactive decay of large atoms --used for nuclear power • Fusion=combining small nuclei --occurs naturally in stars --prospects for nuclear energy—no radioactive byproducts Both are transmutations—one nuclide is converted into another Consider the relationships • • • • Half life Original amount Final amount Time elapsed Consider the relationships t/t1/2 A=A0(1/2) • • • • A is the amount of the sample remaining A0 is the original amount in the sample t is the time that has passed, and t 1/2 is the half-life of the nuclide Please notice t/t1/2 A=A0(1/2) • A / A0 is the fraction remaining • t / t 1/2 is the number of half-lifes that have passed Try it. • Hydrogen-3 has a half life of 12.3 years. If you start with a 20 g sample of H-3 --how much is left after 12.3 years? --how much is left after 24.6 years? --how much is left after 30.2 years? Try it. • Br-82 has a half life of 35.3 hours. If you start with a 6.5 mg sample of Br-82 --how much is left after 4 days? --how long will it take to reach .75 mg? Try it. • Br-82 has a half life of 35.3 hours. If you start with a 6.5 mg sample of Br-82 --how much is left after 4 days? --how long will it take to reach .75 mg? How do you solve for an exponent? Use a log function t/t1/2 log (A/A0)= log(1/2) log (A/A0)=t/t1/2log(1/2) t/t1/2 = log (A/A0) log(1/2) Try it. • Br-82 has a half life of 35.3 hours. If you start with a 6.5 mg sample of Br-82 --how much is left after 4 days? --how long will it take to reach .75 mg? Try it. • If you start with 1.38 mg of U-234 and t1/2=2.44 x 105 yrs for its decay: --how much is left after 20,000 years? --how long will it take to reach 0.40 mg? Try it. • A .350 mg sample of K-42 decays to only .066 mg in 29.7 hours. --what is the half life? --how much was left after 20.0 hours? --how long will it take to reach .010 mg? Th-th-that’s all, folks. Atomic theory • All matter is composed of atoms. --atoms of one element are identical --atoms of different elements are different --reactions form different combinations of atoms, not different atoms • Atoms are composed of protons, neutrons, and electrons. (Are all of the little kids in bed?—Now we can tell you the real story…) Modern Theory In this Universe, you will find: Fermions and Bosons (force mediating particles) Modern Theory Bosons (force mediating particles) include: g, (electromagnetic force) Zo, (weak nuclear force) Gluons (Strong nuclear force) Graviton (gravity) W±, (weak nuclear force) Higgs (mediates mass) Modern Theory Fermions are the fundamental particles, including: Quarks and Leptons Modern Theory up down Types of quarks include: top (formerly known as truth) charm bottom (formerly known as beauty) strange (and their antiparticles) Modern Theory Leptons include: Electrons, e-, Muons, m, Tauons, t, and three types of neutrinos e, m, t (and their antiparticles) Modern Theory Combinations of quarks make hadrons, either: Mesons (2 quarks each) Including: p+, K-, r+, B0, c Baryons (3 quarks each) including p, n, p-, L, - Modern Theory In this Universe, you will find fermions which include the fundamental particles Quarks u,d,c,s,t,b (and antiparticles) Quarks make up the hadrons, either and Bosons (force mediating particles) g, (electromagnetic force Zo, (weak nuclear force) Gluons (Str. nuclear force) Graviton (gravity) W±,(weak nuclear force) Higgs (mediates mass) Leptons e-,m,t,e, m, t (and antiparticles) Mesons (2 quarks each) p+,K-,r,+B0,c baryons (3 quarks each) including p,n,p-,L,-