Potassium permanganate (KMnO 4 ) is sometimes added to water as it enters a drin

Question

Potassium permanganate (KMnO4) is sometimes added to water as it enters a drinking water treatment plant to assist in the removal of Fe2+ and Mn2+ ions. The KMnO4 oxidizes those cations by acquiring electrons according to the following reaction:

KMnO4 + 4H+ + 3e- K+ + MnO2(s) + 2H2O

a) What is the (electron) equivalent weight of Mn, based on this reaction?

b) Calculate the mass (g) of KMnO4 in 2 L of a 0.15 M KMnO4 solution.

c) If 1.0 mL of 0.15 M KMnO4 is added to each liter of the drinking water, and all the KMnO4 undergoes the reaction shown, what concentration of KMnO4 will be generated by the reaction, in ppm?

Explanation / Answer

a)  KMnO4 as an oxidizer in acidic media:

MnO4- + 8 H+ + 5e- --> Mn2+ + 4H2O(gained 5 electrons from reductant)

I.e. Eq. wt. of Mn = molar mass of KMnO4 / 5.0 = 158.04/5 = 31.61 grams/equivalent

b) moles of KMnO4 =( 0.15 mol/L )/ 2.0 L ) x molar mass of KMnO4

= 11.853 g

c) moles of KMno4 = ( 0.15 mol/L )/ 10^-3 L ) x molar mass of KMnO4

= 0.0237 mol

and therefore moles of KMnO4 gives moles of MnO2.

molarity of MnO2 = ( 0.0237 moles / molar mass of MnO2 ) / 1.0 L

= ( 0.0237 moles / 86.9368 g/mol ) / 1.0 L

= 2.73 x 10^-4 M

= 273 ppm

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.