AP Chemistry Oxidation-Reduction Reaction Titration

Question

Write the balanced net ionic equation for the reaction between MnO4
ions and H2C2O4 in acid solution

.
2 . H ow many moles of Fe2 + ions can be ox i d i zed by 0.043 moles of MnO4 i o n s ?

3 . 1.630 g of iron ore is dissolved in an acidic solution. This solution is titrated to a pink endpoint
with 27.15 mL of a 0.020 M KMnO4 s o l u t i o n .

 

a. How many moles of MnO4 ions we re consumed?
b. How many moles of Fe2 + we re in the iron ore sample?
c. What is the percent of iron in the iron ore sample?

Answer 1

Do you know how to write oxidation/reduction half reactions? If not, you must learn. 

 

(1)  2 MnO₄^- +5 H₂C₂O₄ + 6 H⁺ =2 Mn²⁺ +10 CO₂ + 8 H₂O

(2)  MnO₄^- + 5 Fe²⁺ + 8 H⁺ = Mn²⁺ + 5 Fe³⁺ + 4 H₂O
Moles Fe²⁺ = 5 x 0.043 moles = 0.215 moles

(3)  moles KMnO₄ = 0.020 mole/L x 0.02715 L= 0.000543 moles MnO4^- consumed
moles Fe²⁺ = 5 moles Fe²⁺ x 0.000543 moles KMnO₄/mole Fe²⁺ = 0.00272 moles Fe²⁺ in sample
mass Fe = 0.00272 mol x 55.847 g/mol=0.152 g
% Fe = 0.152 g/1.630 g (x100%) = 9.33%