Reactions + oxidation

Reactions + oxidation

1. Titrations

   • Must know conc. of one or two solutions
     • Standard solution
       • Use to find unknown info about substance dissolved in 2nd solution
   • Unknown info may be
     • Conc. of solution
     • Molar mass
     • Formula
     • No. of molecules of water of crystallisation
   • Indicators
     • Methyl orange
       • Acid = red; Base = yellow; End point = orange
     • Bromothymol blue
       • Acid = yellow; Base = blue; End point = green
     • Phenolphthalein
       • Acid = colourless; Base = pink; End point = pale pink
   • Calculating unknowns
     • 1st 2 steps the same
       • 1) Calculate amount, in mol, of reactant
         • n = c x V/1000
       • 2) Calculate amount, in mol, of other reactant
         • Stoichiometry
     • 3rd step different
       • Unknown conc.
         • Calculate conc. of unknown
         • c = nx1000 / V
       • Unknown molar mass
         • Calculate molar mass of unknown
         • M = n x m

2. Oxidation number

   • Number of electrons an atom uses to bond with atoms of other elements
   • Rules
     • Uncombined element = 0
     • Combined oxygen = -2
       • When combined with fluorine = +2, in peroxides = -1
     • Combined hydrogen = +1
       • When bonded to metal in hydrides = -1
     • Simple ion = charge on ion
     • Combined fluorine = -1
   • Some elements form compounds and ions in which the element has different oxidation no's
     • Use Roman Numerals
     • Transition elements form ions with different oxidation no's.
   • Oxyanions = negative ions that contain an element with oxygen
     • End in -ate

3. Redox reactions

   • Substance that is reduced takes electrons form substance that is oxidised
   • Half equations show how electrons are transferred
   • Metals = oxidised - lose electrons -> +ve ions
   • Non-metals = reduced - gain electrons -> -ve ions
   • Reduction = decrease in oxidation no. oxidation = increase
   • Metals and acids
     • Metal = oxidised -. +ve metal ions
     • Hydrogen = reduced -> hydrogen gas
     • metal + acid -> salt + H2