Samples containing iron(II) ion can be titrated with solutions containing diehro

Question

Samples containing iron(II) ion can be titrated with solutions containing diehromate ion under acidic conditions. Cr_2O_2^2- + 5Fe^+2 + 14H^+ rightarrow 2Cr^+3 + 6Fe^+3 + 7H_2O If a 3.465 g sample containing iron(II) sulfate is dissolved and requires 52.7 mL of 0.0335 M K_2Cr_2O_2 solution to titrate it what it the percent iron(II) sulfate in the sample? What is the molarity of a potassium permanganate (KMnO_4) solution if 35.6 mL of the solution are needed to titrate a 0.659 g sample of pure sodium oxalate? 2MnO_4^-1 + 5C_2O_4^-2 + 16H^+ rightarrow 2Mn^+2 + 10CO_2 + 8H_2OMolarity of potassium permanganate:

Explanation / Answer

1. no of mole of K2Cr2O7 reacted = 52.7*0.0335/1000 = 0.001765 mole

from equation

1 mole K2Cr2o7 = 6 mole FeSO4

NO OF mole of FeSO4 present in sample = 6*0.001765 = 0.0106 mole

mass of FeSO4 present in sample = 0.0106*Mwt

                                 = 0.0106*152

                                 = 1.611 g

   percent of Feso4 = 1.611/3.465*1000 = 46.5%

2. from equation

2 mole KMnO4 = 5 MOLE oxalate

no of mole of sodium oxalate consumed = 0.6559/134 = 0.0049 mole

no of mole of KMnO4 recated = 2*0.0049/5 = 0.00196 mole

Molarity of KMnO4 recated = n/V = 0.00196/0.0356 = 0.055 M

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