* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Electrochemistry Oxidation – Reduction and Oxidation Numbers
Process chemistry wikipedia , lookup
Nucleophilic acyl substitution wikipedia , lookup
Inorganic chemistry wikipedia , lookup
Bioorthogonal chemistry wikipedia , lookup
Livermorium wikipedia , lookup
Hypervalent molecule wikipedia , lookup
Stoichiometry wikipedia , lookup
Geochemistry wikipedia , lookup
X-ray photoelectron spectroscopy wikipedia , lookup
Citric acid cycle wikipedia , lookup
Resonance (chemistry) wikipedia , lookup
Coordination complex wikipedia , lookup
Atomic orbital wikipedia , lookup
Marcus theory wikipedia , lookup
Artificial photosynthesis wikipedia , lookup
Electrolysis of water wikipedia , lookup
Click chemistry wikipedia , lookup
Electronegativity wikipedia , lookup
Hydrogen-bond catalysis wikipedia , lookup
Metallic bonding wikipedia , lookup
Acid–base reaction wikipedia , lookup
Rutherford backscattering spectrometry wikipedia , lookup
Lewis acid catalysis wikipedia , lookup
Total organic carbon wikipedia , lookup
Chemical bond wikipedia , lookup
IUPAC nomenclature of inorganic chemistry 2005 wikipedia , lookup
Water splitting wikipedia , lookup
Microbial metabolism wikipedia , lookup
History of molecular theory wikipedia , lookup
Oxidative phosphorylation wikipedia , lookup
Electron configuration wikipedia , lookup
Chemical reaction wikipedia , lookup
Photosynthetic reaction centre wikipedia , lookup
Atomic theory wikipedia , lookup
Strychnine total synthesis wikipedia , lookup
Extended periodic table wikipedia , lookup
Photoredox catalysis wikipedia , lookup
Electrochemistry wikipedia , lookup
Evolution of metal ions in biological systems wikipedia , lookup
Oxidation state wikipedia , lookup
Electrochemistry Oxidation – Reduction and Oxidation Numbers Many important chemical reactions involve the transfer of electrons. e.g. 2Na + Cl2 Æ 2 NaCl Many do not. e.g. Pb(NO3)2(aq) + 2KI(aq) Æ PbI2(s) + 2KNO3(aq) Chemists have devised a useful bookkeeping method to determine if electron transfer is involved in a chemical reaction. It is referred to as the oxidation state method. If an atom loses electrons, it is oxidized. If an atom gains electrons, it is reduced. The oxidation state or equivalently, the oxidation number, of an atom is the charge assigned to an atom using the oxidation state method. Rules for assigning oxidation numbers: 1. Elements in their most abundant naturally occurring form are assigned an oxidation number of zero. e.g. Na, Fe, Cl2, O2 2. The sum of the oxidation numbers for a compound or formula unit is zero. 3. For a polyatomic ion, the oxidation numbers of the constituent atoms sums to the ion charge. 4. Monatomic ions are assigned oxidation numbers equal to the ion charge. e.g., Na+ = +1, Al3+ = +3, Cl- = -1, N3- = -3 5. Oxygen in a compound or ion usually has an oxidation state of –2. (Peroxides are the exception, in which case the oxidation number is –1.) 6. Hydrogen in a compound or ion usually has an oxidation state of +1. (Hydrides are the exception, in which case the oxidation number is –1.) 7. For covalently bonded substances, shared electrons are assigned to the more electronegative element. 8. When two atoms of the same element share electrons, they are divided equally between the atoms (each atom gets half.) Determining oxidation numbers from a formula is usually an exercise in solving for the unknown oxidation number of one if the elements in the formula. Procedure for assigning an oxidation number: 1. List the known oxidation numbers of all atoms in the compound or ion. 2. Multiply each oxidation number by the relevant number of atoms. 3. Determine the difference between the sum of the oxidation numbers of the known atoms and the total charge of the molecule or ion. 4. Divide the difference by the number of atoms of the unknown oxidation state. e.g. K2Cr2O7 O = -2; K = +1; solve for Cr 0 = 7(-2) + 2(+1) + 2(oxidation number of Cr) +12 = 2(oxidation number of Cr) +6 = oxidation number of Cr e.g NaNO3 O = -2; Na = +1; solve for N 0 = 3(-2) + 1(+1) + (oxidation number of N) +5 = oxidation number of N Acid-Base reactions: H+ transfer AcidA + BaseB BaseA + AcidB AcidA,BaseA are protonated and deprotonated forms of A. They constitute a conjugate acid-base pair. (The same holds for BaseB, AcidB.) Oxidation-Reduction reactions: e- transfer AOX + BRED ARED + BOX AOX, ARED are oxidized and reduced forms of A. BOX, BRED are oxidized and reduced forms of B. AOX and BOX are oxidizing agents ARED and BRED are reducing agents AOX oxidizes BRED and BRED reduces AOX In acid-base chemistry we speak in terms of strong acids and bases and weak acids and bases. We also speak of strong and oxidizing agents and strong and weak reducing agents…. Strong oxidizing agents have high electron affinities. Strong reducing agents readily donate electrons. Balancing oxidation/reduction reactions: as always, the conservation laws must be obeyed the half reaction method (two examples: acid solution, base solution) In acid solution: consider the unbalanced net reaction: MnO4- + C2O42- Mn2+ + CO2 Step 1: write the half reactions (for each redox pair) (i.e. AOX ARED; BRED BOX) MnO4- C2O42- Mn2+ CO2 Step 2: balance each half reaction using H2O, H+, and e-, as needed MnO4- + 8H+ + 5eC2O42- Mn2+ + 4H2O 2CO2 + 2e- Step 3: multiply each half reaction as needed to balance the number of electrons on each side and add the half reactions 2(MnO4- + 8H+ + 5e- Mn2+ + 4H2O) 5(C2O422CO2 + 2e-) ___________________________________________ 2MnO4- + 16H+ + 5C2O42- 2Mn2+ + 8H2O + 10CO2 In base solution: MnO4- + C2O42- Mn2+ + CO2 Step 1: write the half reactions (for each redox pair) (i.e. AOX ARED; BRED BOX) MnO4- C2O42- Mn2+ CO2 Step 2: balance each half reaction using H2O, OH-, and e-, as needed MnO4- + 4H2O + 5eC2O42- Mn2+ + 8OH- 2CO2 + 2e- Step 3: multiply each half reaction as needed to balance the number of electrons on each side and add the half reactions 2(MnO4- + 4H2O + 5e- Mn2+ + 8OH-) 5(C2O422CO2 + 2e-) ___________________________________________ 2MnO4- + 8H2O + 5C2O42- 2Mn2+ + 16OH- + 10CO2 n = #electrons transferred = 10 Ex. 2 H3AsO3 + I2 H3AsO4 + I- In acid: H3AsO3 + H2O H3AsO4 +2H+ + 2e- I2 + 2e2I___________________________________________ H3AsO3 + I2 + H2O H3AsO4 + 2I- + 2H+ In base: H3AsO3 + 2OH- H3AsO4 + H2O + 2e- I2 + 2e2I___________________________________________ H3AsO3 + I2 + 2OHH3AsO4 + 2I- + H2O n = #electrons transferred = 2