   Chapter 4, Problem 75PS

Chapter
Section
Textbook Problem

To analyze an iron-containing compound, you convert all the iron to Fe2+ in aqueous solution and then titrate the solution with standardized KMnO4. The balanced, net ionic equation isMnO4–(aq) + 5 Fe2(aq) + 8 H3O+(aq) → Mn2(aq) + 5 Fe3+(aq) + 12 H2O(l)A 0.598-g sample of the iron-containing compound requires 22.25 mL of 0.0123 M KMnO4 for titration to the equivalence point. What is the mass percent of iron in the sample?

Interpretation Introduction

Interpretation:

The mass percent of iron in the given sample has to be determined.

Concept introduction:

• The relation between the number of moles and mass of the substance is ,

Numberofmole=MassingramMolarmass

Mass in gram of the substance= Numberofmole×Molarmass

• The molar mass of an element or compound is the mass in grams of 1 mole of that substance, and it is expressed in the unit of grams per mol (g/mol).
• For chemical reaction balanced chemical reaction equation written in accordance with the Law of conservation of mass.
• Law of conservation of mass states that for a reaction total mass of the reactant and product must be equal.
• Stoichiometric factor is a relationship between reactant and product which is obtained from the balanced chemical equation for a particular reaction.
• Amountof substance=Concentrationofsubstance×volumeofthesubstance
• Mass percent of elements of a compound is the ratio of mass of element to the mass of whole compound and multiplied with hundred.
• Titration is a method to determine the concentration of a substance in solution by adding a solution of known volume and concentration until the reaction is completed.
Explanation

Balanced chemical equation for the given reaction is,

MnO4-(aq)+5Fe2+(aq)+8H3O+(aq)Mn2+(aq)+5Fe3+(aq)+12H2O(l)

From the balanced chemical equation it is clear that potassium permanganate (KMnO4) and iron (Fe) react in a 1:5ratio.

The amount (moles) of KMnO4 used in the titration can be calculated from its volume and concentration as follows,

AmountofKMnO4 =CKMnO4×VKMnO4 =0

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