Chemistry I Laboratory Manual, 2017 Revision Qnestions: 1) Samples containing ir

Question

Chemistry I Laboratory Manual, 2017 Revision Qnestions: 1) Samples containing iron(II) ion can be titrated with solutions containing dichromate 0 ion under acidic conditions. (a) Which ion is oxidized in this reaction? (b) Which ion is the reducing agent in this reaction? (c) Ifa 1.818 g sample containing iron(Il) sulfase is dissolved and requires 32.1 mL of 0.0100 MK,CrO, solution to titrate it, what is the percent iron(Il) sulfate in the sample? 2) What volume of a 0.0225 M solution of potassium permanganate are required to titrate 0.461 g of sample that is 69.9% sodium oxalate?

Explanation / Answer

from equation

1 mol K2Cr2O7 = 6 mol FeSO4

a) oxidized ion = Fe^2+

b) reducingagent = Fe2+ (which involves in oxidation)

c) no of mol of K2Cr2o7 = 32.1*0.01/1000 = 0.000321 mol

   no of mol of FeSO4 reacted = 6*0.000321 mol

                             = 0.001926 mol

   mass of FeSO4 PRESENT in sample = 0.001926*152 = 0.293 g

   percent Fe2+ = 0.293/1.818*100 = 16.12%

2)    KmNo4 vs oxalate

2 mol KMnO4 = 5 mol sodium oxalate

mass of sodium oxalate = 0.461*69.9/100 = 0.322 g

no of mol of sodium oxalate = 0.322/134 = 0.0024 mol

no of mol of KMnO4 reacted = 0.322*2/5 = 0.13 mol

volume of KMnO4 reacted = 0.13/0.0225 = 5.78 ML

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