Quantitative Exam F326

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  • Created by: Labake
  • Created on: 15-10-14 21:25
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  • Quantitative Exam F326
    • You will prepare a solution of an acid and carry out a redox titration of this solution
      • "You will prepare a soultion"
        • Need accuracy and precision when measuring
          • Log measurements to correct decimal place
            • Use error of precision for each piece of equipment
              • Measuring Cylinder= +/-1cm3, all reading to 0 decimal places, times 1 by number of times measuring cylinder used
              • Mass balance= +/-0.01cm3, all reading to 2 decimal places ending in any number
              • Burrete = +/-0.05cm3 so all readings to 2 decimal places and end in 0 or 5 (times 0.05 by number of times burette used e.g. x2)
              • % ERRORS- Mass= (0.01 x no. of readings(2)/ total mass)x 100
              • % ERRORS- Burette= (0.05 x no. of readings(2)/ total mean vol.) x 100
              • % ERRORS- Measuring Cylinder =(1 x no. of readings/ total vol.) x 100
      • "carry out a redox tritation"
        • Be CONFIDENT with Redox specification
          • E.g. Half Equations, Overall equations (by balancing electrons with common factor or assuming ration of 1:1)
          • E.g. Redox Calculations- Moles and Observations
            • Obsevations
              • MnO4- to Mn2+ = purple to colourless (end point) or pale pink (by drop) (reduction)
              • Fe2+ to Fe3+ and e- = pale green to pale yellow (oxidation)
              • Br- to Br2= colourless to orange (oxidation)
              • I- to I2 + e- =colourless to brown (oxidation)
              • Alcohol to Aldehyde = orange to green (using acidified potassium dichromate Cr2O7^2- to Cr3+ (reduction)
            • Moles
              • Given gdm-3 - divide this by Mr for concentration - moldm-3
                • Known conc., times this by volume (over 1000) for moles
                  • Ratio of compound to unknown compound
                    • Scale up or down in moles (x or / by 10) for moles of unknown compound
                      • Mr of unknown compound = mass/moles
                        • Find x= Mr on compound - Mr of anhydrous version = A
                          • A / 18 = x
              • A / 18 = x
      • "titration"
        • Getting 2 concordant (similar) volumes of a solution
          • Don't use trial results
          • Burette= +/-0.05 x 2 readings = concordant value- error of +/-0.1cm3
        • Getting moles =  use mean of titres for ACCURACY and PRECISION- no anomalies
          • Record mean to 1 decimal place (2 readings x 0.5)
    • 5Fe2+(aq) + MnO4-(aq) + 8H+(aq)-->5Fe3+(aq) + Mn2+(aq) + 4H2O
    • 2MnO4- + 5H2O2 + 6H+ --> 2Mn2+ + 5O2(g) + 8H2O(l)
    • 2 (S2O3)2- (aq) + I2 (aq)--> (S4O6)2-(aq) + 2 I- (aq)

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