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Electrochemistry. Determine the oxidation numbers for atoms in compounds and ions Identify reactions as redox or non-redox Include: oxidizing agent, reducing agent. Additional KEY Terms. both atoms and the electrons must be balanced in redox reactions. x 2 atoms = 2e -.
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Determine the oxidation numbersfor atoms in compounds and ions • Identify reactions as redox or non-redox • Include: oxidizing agent, reducing agent Additional KEY Terms
both atomsand the electronsmust be balancedin redoxreactions x 2 atoms = 2e- gains 1e- 0 +1 -1 0 oxidation numbers: 2 Cu + Cl2 → Cu+ + Cl- 2 2 x 2 = 2e- loses 1e- • done by assigningoxidation numbers to allelements
**There is a written difference between ion charge and oxidation number** Mg (s) + Cl2 (g) → MgCl2 (s) Cl + 1e- → Cl1- Mg → Mg2+ + 2e- Magnesium ion ion charge: 2+ oxidation #:+2 Chlorine ion ion charge: 1- oxidation #:-1 Sometimes these numbers are the same (like above) sometimes they are very different – which is why we write them differently
Oxidation number represents the chargethe atom would haveifevery bond were ionic. O#s are based on the electronegativity of the atoms 1. Assign known numbers first, calculate others. • All uncombinedelements (& diatomics) – zero O2 0 Cu 0 • Monatomic ion -equals ion charge Cl- -1 Fe3+ +3
Alkalimetals (IA)– always +1 • Earth metals (IIA)– always +2 • Halogens(VIA) – usually-1 • Hydrogen– usually+1 • Oxygen – usually-2 Except metal hydrides (NaH) Except peroxides (H2O2) • 2. Neutral compound: • Sumof O#s must equal zero • 3. Charged compound: • Sum of O#s must equalcharge of compound
2. Neutral compound: • Sum of O# must equal zero Assign O#s for each atom in K2Cr2O7 Step 1: Start with atoms which are known. O: –2 K: +1 Step 2: Solve for other atoms. +6 +1 Multiple the O#s by the subscripts for each atom to get the sum -2 2 K2CrO7 +2 ?? +12 = 0 -14 K = +1 Cr = +6 O = –2.
3. Charged compound: • Sum of O# must equalcharge of compound Assign O#s for each atom in NO3- Step 1: Start with atoms which are known. O: –2 Step 2: Solve for other atoms. -2 +5 NO3- +5 = -1 -6 ?? N = +5 O = –2.
Use ox.numbers to determine if reaction is a redox reaction. -2 +1 -2 +4 +4 +1 -2 SO2 + H2O → H2SO3 +4 -2 +2 -4 +2 -6 +4 Remember: Redox involves the transfer of electrons – no change in O#s during the reaction means NO redox NOT a redox reaction
Is the following reaction a redox reaction? -2 +5 0 +1 -2 +1 +5 0 Cu(s) + 2 AgNO3(aq) → CuNO3(aq) + 2 Ag(s) 0 +5 +1 -6 +5 +1 0 -6 Oxidation cannot occur without reduction Redox reaction • Cu – oxidized(loss of electrons) • Ag – reduced(gain of electrons)
Oxidizing agent - causes the oxidation of another substance. AgNO3 is the oxidizing agent Reducing agent - causes the reduction of another substance. Cu is the reducing agent Think opposites: if the compound is the “oxidizing agent” of the reaction, then it is reduced in the process and vice versa +1 0 Cu(s) + 2 AgNO3(aq) → CuNO3(aq) + 2 Ag(s) +1 0
Identify the substance oxidized, the substance reduced, the oxidizing agent and the reducing agent. +1 0 -2 +2 -2 -2 +1 +1 +5 -2 2 HNO3(aq) + 3 H2S(g) → 2 NO(g) + 3 S(s) + 4 H2O(l) +2 0 +5 +1 -2 +2 -2 +2 -6 -2 S – oxidized N – reduced H2S – reducing agent HNO3 – oxidizing agent Substance - means element Agent – means compound
How many electrons are transferred in the reaction below: gains 3e- +1 0 -2 +2 -2 -2 +1 +1 +5 -2 3 HNO3(aq) + H2S(g) → 2 NO(g) + 3 S(s) + 4 H2O(l) 2 loses 2e- Stoichiometry (coefficients and subscripts) used to determined total electronstransferred S: (3 atoms) x (2e- lost) = 6 electrons lost N: (2 atoms) x (3e- gained) = 6 electrons gained
CAN YOU / HAVE YOU? • Determine the oxidation numbersfor atoms in compounds and ions • Identify reactions as redox or non-redox • Include: oxidizing agent, reducing agent Additional KEY Terms
