   Chapter 3, Problem 101SCQ

Chapter
Section
Textbook Problem

The presence of arsenic in a sample that may also contain another Group 5A element, antimony, can be confirmed by first precipitating the As3+ and Sb3+ ions as yellow solid As2S3 and orange solid Sb2S3. If aqueous HCI is then added, only Sb2S3 dissolves, leaving behind solid As2S3. The As2S3 can then be dissolved using aqueous HNO3.3 As2S3(s) + 10 HNO3(aq) + 4 H2O(ℓ) → 6 H3AsO4(aq) + 10 NO(g) + 9 S(s)Finally, the presence of arsenic is confirmed by adding AgNO3 to the solution of H3AsO4 to precipitate a reddish brown solid AgxAsOy The composition of this solid is As, 16.199% and Ag, 69.964%.(a) What are the oxidation numbers of As, S, and N in the reaction of As2S3 with nitric acid?(b) What is the formula of the reddish brown solid AgxAsOy?

(a)

Interpretation Introduction

Interpretation:

The oxidation number of As, S and N in the reaction of As2S3 with Nitric acid should be determined.

Concept introduction:

An oxidizing agent gains the electrons and is reduced in a chemical reaction and it is electron acceptor.  A reducing agent loses electrons and is oxidized in a chemical reaction and it is electron donor.

The oxidation state is called as oxidation number, which describes degree of oxidation (loss of electrons) of an atom in a chemical compound.  Theoretically, the oxidation state is positive, negative or zero.

The calculation of the empirical formula of the compound is shown below,

Explanation

The oxidation state of the sulfur in the reactant is -2,

The oxidation state of the Arsenic in the reactant is shown below,

Net charge = Number of oxidation state of arsenic atom+Number of oxidation state ofsulfur atom 0 = 2(x) +  3(-2)0= 2(x) +  3(-2)0 = 2x- 63 = xX = 3

The oxidation state of the nitrogen in the reactant is shown below,

Net charge = Number of oxidation state of hydrogen atom+Number of oxidation state ofnitrogen atom + Number of oxidation state ofoxygen atom 0 = x +  3(-2)+10= x +  3(-2)+10 = x- 6 +15 = x<

(b)

Interpretation Introduction

Interpretation:

The formula of reddish brown solid AgxAsOy should be identified.

Concept introduction:

Get the mass of each element by assuming a certain overall mass for the sample.  Convert the mass of each element to moles of each element using the atomic masses.  Find the ratio or the moles of each element by dividing the number of moles of each by the smallest number of moles.

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