Acids and redox continued

Acids and redox continued

1. Oxidation Numbers

   • Oxidation numbers are a measure of how many electrons that an atom uses to bond with atoms of another element.
   • Both covalent and ionic compounds can be assigned oxidation number
   • Examples
     • Elements
       • Oxidation Number: 0
       • Such as O2, H2, Fe, S8
       • There are no exceptions
     • Combined H
       • Such as H20 NH3
       • Oxidation Number: +1
       • Exceptions
         • -1 In metal hydrides E.g. NaH, CaH2
     • Combined O
       • Such as H20 CaO
       • Oxidation Number: -2
       • Exceptions
         • -1 in peroxides E.g H202
         • +2 when bonded to F -> F20
     • Combined F
       • Oxidation Number: -1
       • Such as HF
       • There are no exceptions
     • Ions
       • Oxidation number = charge on ion
       • Such as Na+ = +1 Mg2+ = +2
   • Transition metals
     • Can have variable oxidation numbers
       • E.g. Fe can exist with oxidation numbers of +2 and +3
       • To diferentiate between states of these metals the oxidation number is given as roman numerals in brackets
     • Examples
       • Iron (II): Fe2+
       • Iron (III): Fe3+
       • Copper (II): Cu2+
       • Copper (I): Cu+

2. Oxyanions

   • Negative molecular ions
   • Contain oxygen
   • Combined with a second element
     • second element has several oxidation states
       • Oxidation number of the second element given in brackets after the name of the name of the oxyanion
   • Examples
     • ions
       • Sulfate (VI) SO4 2-
       • Carbonate (IV) CO3 2-
       • Nitrate (V) NO3 -
     • Compounds
       • Sodium Nitrate (V) NaNO3
       • Calcium Sulphate (VI) CaSO4
       • Potassium Manganate (VII) KMnO4
   • Name usually ends in 'ate'

3. Redox Reactions

   • Definitions: Oxidation is the loss of electrons
   • Definitions: Reduction is the gain of electrons
   • Remember, OIL RIG
   • Oxidation is the increase in oxidation number
   • Reduction is the decrease in oxidation number
   • <---------------Oxidised----------------- X3+ X2+ X+ X- X2- X3- -----------------Reduced---------------->
   • Definition: A Redox reaction is one of which involves both oxidation and reduction
     • An example of a Redox reaction is the reaction of dilute acids and metals to form a salt and hydrogen
   • A Reducing agent is Oxidised
     • An Oxidising agent is Reduced