# Quantitative Exam F326

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• Created by: Labake
• Created on: 15-10-14 21:25
• 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)