violinplayer.gifgradu8doc.gifAdvanced Level Chemistry - Redox Volumetric Titration Question 1 - ANSWERS


Site Meter Fill in all the gaps, then press "CHECK" at any time, as long as you are not bothered about the score! You can bookmark this page, print it out, try the Q and go back on-line to CHECK!!! Thoughts on style of question? Updated Doc Brown's Chemistry Clinic June 22nd 2009

Q1 ANSWERS
(a) MnO4-(aq) + 8H+(aq) + 5Fe2+(aq) ==> Mn2+(aq) + 5Fe3+(aq) + 4H2O(l)

(b) (i) mol MnO4- = 0.02[2dp] x 24.3[1dp] / 1000[4sf] = 0.000486[6dp]

mol Fe2+ = 5 x 0.000486[6dp] (from 1 MnO4- : 5 Fe2+ in equation)
mol Fe2+ = 0.00243[5dp] in 20 cm3[2sf]

so scaling up to 1 dm3, molarity of Fe2+ = 0.00243[5dp] x 1000[4sf] / 20[2sf]
molarity Fe2+ = 0.1215 mol dm-3 [4dp]

(ii) The end point is the first faint permanent pink due to a trace of excess KMnO4

(c) mol MnO4- = 0.02[2dp] x 25.45[4sf] / 1000 = 0.000509 [6dp]

mol Fe = mol Fe2+ = 5 x 0.000509[6dp] = 0.002545 [6dp]

mass Fe = 0.002545 x 55.9[1dp] = 0.1423g [4dp] per titration.

total Fe in wire = 0.1423 x 10[2sf] = 1.423g (1/10th of the made up solution used in titration)

so % Fe = 1.423[3dp] x 100 / 1.51 = 94.2% [3sf]