Oxidation Number to understand redox reaction

Redox oxidation

1. Quick Quiz What is the total oxidation number for a compound? Zero What is the total oxidation for a sulfate ion? –2 What is the normal oxidation state for a group 2 metal? +2 What is the oxidation number for a halogen? –1 What is the oxidation number for oxygen in a peroxide? –1 What does the name Copper (II) Oxide tell us? Copper has an oxidation state of +2.

2. Oxidation Number 2.1.5.1 Objective: Assign oxidation numbers to elements within a compound. Outcomes: Must: State the rules for assigning oxidation numbers. Should: Determine the oxidation numbers for elements within simple compounds and ions. Could: Apply the oxidation rules to determine the formula of compound. Specification Links: Module: 2. Foundations in Chemistry. Unit: 1. Atoms & Reactions. Sub-Unit: 5. Redox.

3. Specification Points Covered 2.1.5 Oxidation Number Use rules for assigning and calculating oxidation number for atoms in elements, compounds and ions. Write formulae using oxidation numbers. Use Roman numerals to indicate the magnitude of the oxidation number when an element may have compounds/ions with different oxidation numbers.

4. The Rules An oxidation number/state shows the charge on an atom if all of its bonds were considered totally ionic. Elements in their natural state = 0 The total oxidation states in a molecule = 0 The total oxidation states in an ion = the charge. Priorities Elements State Exception Group 1, 2 and 3 +1, +2 and +3 Fluorine -1 Hydrogen +1 -1 Metal Hydrides ( LiH ) Oxygen -2 -1 Peroxides (H 2 O 2 ) Chlorine -1 + (Varies) Chlorates

5. Worked Examples Find the oxidation number of Mn in KMnO 4 . Find the overall compound charge. Find the priorities. K = +1 O = -2 Substitute the oxidation numbers into the formula: 0 = K + Mn + 4(O) 0 = +1 + Mn + 4(-2) = +1 + Mn + -8 +8 = +1 + Mn +7 = Mn

6. Worked Examples Find the oxidation number of Cr in Cr 2 O 7 2- . Find the overall compound charge. 2- Find the priorities. O = -2 Substitute the oxidation numbers into the formula: -2 = 2(Cr) + 7(O) -2 = 2(Cr) + 7(-2) = 2(Cr) + -14 +12 = 2 x Cr +6 = Cr

7. Questions What is the oxidation state of: O in Al 2 O 3 Cl in ClO 4 – I in IO 3 – N in NO 2 S in H 2 SO 4 V in V 2 O 5 P in P 4 O 10 Cu in CuCl Cl in KClO 3 Cu in Cu(NO 3 ) 2 O in H 2 O 2 S in H 2 SO 3 Determine the molecular formula for the these compounds: Magnesium Iodide Iron oxide (Fe = +3) Aluminium Sulfide Calcium Carbonate Ammonium vanadate (V = +5)

8. Questions What is the oxidation state of: O = -2 Cl = +7 I = +5 N = +4 S = +6 V = +5 P = +5 Cu = +1 Cl = +5 Cu = +2 O = -1 S = +4 Determine the molecular formula for the these compounds: MgI 2 Fe 2 O 3 Al 2 S 3 CaCO 3 NH 4 VO 3

9. Naming Compounds Roman numerals are used to show the oxidation state of a compound within a compound. Potassium Manganate (VII) – KMnO 4 . Potassium Manganate (VI) – K 2 MnO 4 . 0 = 2(+1) + Mn + 4(-2) = +2 + Mn + -8  +8 = +2 + Mn  +6 = Mn Metals are followed by its oxidation number unless it only has the one i.e. Group 1, 2 and 13.

10. Questions Name these compounds: CuO FeF 3 Cr 2 (SO 4 ) 3 Ca(IO 3 ) 2 CrF 3 CrI 2 CoBr 2 Cu 2 O Fe(OH) 3 FeS PbCO 3 PbCl 2 Mn 2 O 7 MnO 3 Na 2 SO 3 KClO 5

11. Questions Name these compounds: Copper (II) Oxide Iron (III) Fluoride Chromium (III) Sulfate Calcium Iodate (V) Chromium (III) Fluoride Chromium (II) Iodide Cobalt (II) Bromide Copper (I) Oxide Iron (III) Hydroxide Iron (II) Sulfide Lead (II) Carbonate Lead (II) Chloride Manganese (VII) Oxide Manganese (VI) Oxide Sodium Sulfate (IV) Potassium Chlorate (IX)

12. Questions Complete this table: Formula Oxidation State of Nitrogen Nitrogen Species Name N 2     NO 3 -     NO 2 -     NH 3     NH 4 +     N 2 O     NO     NO 2    

13. Questions Complete this table: Formula Oxidation State of Nitrogen Nitrogen Species Name N 2 0  Nitrogen  NO 3 -  +5  Nitrate (V) NO 2 -  +3  Nitrate (III) NH 3  -3  Ammonia NH 4 +  -3 Ammonium N 2 O  +1  Nitrogen (I) Oxide NO  +2  Nitrogen (II) Oxide NO 2  +4  Nitrogen (IV) Oxide

14. Next Lesson For next lesson read and make notes on: Oxford: Pages 50-51 (Redox Reactions) Hodder Book 1: Pages 78-79 Pearson Book 1: Pages 68-69