   # A compound has been isolated that can have either of two possible formulas: (a) K[Fe(C 2 O 4 ) 2 (H 2 O) 2 ] or (b) K 3 [Fe(C 2 O 4 ) 3 ]. To find which is correct, you dissolve a weighed sample of the compound in acid, forming oxalic acid, H 2 C 2 O 4 . You then titrate this acid with potassium permanganate; KMnO 4 (the source of the MnO 4 − ion). The balanced, net ionic equation for the titration is 5 H 2 C 2 O 4 (aq) + 2 MnO 4 − (aq) + 6 H 3 O + (aq) → 2 Mn 2+ (aq) + 10 CO 2 (g) + 14 H 2 O( ℓ ) Titration of 1.356 g of the compound requires 34.50 mL of 0.108 M KMnO 4 . Which is the correct formula of the iron-containing compound: (a) or (b)? ### Chemistry & Chemical Reactivity

9th Edition
John C. Kotz + 3 others
Publisher: Cengage Learning
ISBN: 9781133949640

#### Solutions

Chapter
Section ### Chemistry & Chemical Reactivity

9th Edition
John C. Kotz + 3 others
Publisher: Cengage Learning
ISBN: 9781133949640
Chapter 4, Problem 126IL
Textbook Problem
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## A compound has been isolated that can have either of two possible formulas: (a) K[Fe(C2O4)2(H2O)2] or (b) K3[Fe(C2O4)3]. To find which is correct, you dissolve a weighed sample of the compound in acid, forming oxalic acid, H2C2O4. You then titrate this acid with potassium permanganate; KMnO4 (the source of the MnO4− ion). The balanced, net ionic equation for the titration is5 H2C2O4 (aq) + 2 MnO4− (aq) + 6 H3O+(aq) → 2 Mn2+(aq) + 10 CO2(g) + 14 H2O(ℓ)Titration of 1.356 g of the compound requires 34.50 mL of 0.108 M KMnO4. Which is the correct formula of the iron-containing compound: (a) or (b)?

Interpretation Introduction

Interpretation:

The correct formula of iron containing compound has to be determined.

Concept introduction:

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

Numberofmole=Mass in gramMolarmass

Mass in gramofthesubstance=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

### Explanation of Solution

Herein two iron compounds are given

1. (a) K[Fe(C2O4)2(H2O)2]
2. (b) K3[Fe(C2O4)3]

To find which one is correct, a weighed sample of the compound is dissolved in acid forming oxalic acid.  This acid is titrated with potassium permanganate.  The balanced net ionic equation for the titration is,

5H2C2O4(aq)+2MnO(aq)+6H3O(aq)+2Mn(aq)2++10CO2(g)+14H2O(l)

Amount of KMnO4 in 34.50mLof0.108MKMnO4 is,

Amountof KMnO4=0.108molL×0.0345=0.003726molKMnO4

Molecular mass of K[Fe(C2O4)2(H2O)2] is 307.0119g/mol and the balanced chemical equation for the reaction of K[Fe(C2O4)2(H2O)2] with KMnO4 is,

K[Fe(C2O4)2(H2O)2]+4KMnO4K[Fe(MnO4)4(H2O)2]+2K2C2O4

The mass of K[Fe(C2O4)2(H2O)2] can be calculated from the amount of KMnO4 as follows,

0

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