   # You wish to determine the weight percent of copper in a copper-containing alloy. After dissolving a 0.251 -g sample of the alloy in acid, an excess of KI is added, and the Cu 2+ and I − ions undergo the reaction 2 Cu 2+ (aq) + 5 I − (aq) → 2 CuI(s) + I 3 − (aq) The liberated I 3 − is titrated with sodium thiosulfate according to the equation I 3 − (aq) + 2 S 2 O 3 2− (aq) → S 4 O 6 2− (aq) + 3 I − (aq) (a) Designate the oxidizing and reducing agents in the two reactions above. (b) If 26.32 mL of 0.101 M Na 2 S 2 O 3 is required for titration to the equivalence point, what is the weight percent of Cu in the alloy? ### 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 125IL
Textbook Problem
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## You wish to determine the weight percent of copper in a copper-containing alloy. After dissolving a 0.251 -g sample of the alloy in acid, an excess of KI is added, and the Cu2+ and I− ions undergo the reaction2 Cu2+(aq) + 5 I−(aq) → 2 CuI(s) + I3−(aq)The liberated I3− is titrated with sodium thiosulfate according to the equationI3− (aq) + 2 S2O32−(aq) → S4O62−(aq) + 3 I− (aq) (a) Designate the oxidizing and reducing agents in the two reactions above. (b) If 26.32 mL of 0.101 M Na2S2O3 is required for titration to the equivalence point, what is the weight percent of Cu in the alloy?

(a)

Interpretation Introduction

Interpretation:

The weight percent of Cu in the given sample of alloy, oxidizing and reducing agent in the given reactions should be determined.

Concept introduction:

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

Numberofmole=MassingramMolarmass

Massingramofthesubstance=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
• Weight percent of elements of a compound is the ratio of weight of element to the weight of whole compound and multiplied with hundred.
• Oxidizing agent is the reduced (gains electrons) atom to cause another atom to be oxidized
• Reducing agent is the oxidized (loses electron) atom to cause another atom to be reduced.

### Explanation of Solution

The balanced equation for the first reaction is,

2Cu(aq)2++5I(aq)2CuI(s)+I(aq)

In this reaction Cu2+ acts as the oxidizing agent and I acts as the reducing agent

(b)

Interpretation Introduction

Interpretation:

The weight percent of Cu in the given sample of alloy, oxidizing and reducing agent in the given reactions should be determined.

Concept introduction:

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

Numberofmole=MassingramMolarmass

Massingramofthesubstance=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
• Weight percent of elements of a compound is the ratio of weight of element to the weight of whole compound and multiplied with hundred.
• Oxidizing agent is the reduced (gains electrons) atom to cause another atom to be oxidized
• Reducing agent is the oxidized (loses electron) atom to cause another atom to be reduced.

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