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Ch.4 - Reactions in Aqueous Solution
All textbooksBrown 14th EditionCh.4 - Reactions in Aqueous SolutionProblem 113a
Chapter 4, Problem 113a

The arsenic in a 1.22-g sample of a pesticide was converted to AsO43- by suitable chemical treatment. It was then titrated using Ag+ to form Ag3AsO4 as a precipitate. (a) What is the oxidation state of As in AsO43-?

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1
Identify the chemical formula of the arsenate ion, AsO43-, which consists of one arsenic (As) atom and four oxygen (O) atoms.
Recall that the oxidation state of oxygen in most compounds is -2.
Set up an equation to find the oxidation state of arsenic (As). Let the oxidation state of As be x. The sum of the oxidation states in the ion AsO43- must equal the charge of the ion, which is -3.
Write the equation: x + 4(-2) = -3, where x is the oxidation state of As and -2 is the oxidation state of each oxygen atom.
Solve the equation for x to determine the oxidation state of arsenic in AsO43-.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Oxidation State

The oxidation state, or oxidation number, is a measure of the degree of oxidation of an atom in a chemical compound. It indicates the number of electrons that an atom can gain, lose, or share when forming chemical bonds. In the case of polyatomic ions like AsO4^3-, understanding how to assign oxidation states helps determine the charge and the behavior of the element within the compound.
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Polyatomic Ions

Polyatomic ions are ions that consist of two or more atoms bonded together, which collectively carry a charge. In this question, AsO4^3- is a polyatomic ion where arsenic (As) is bonded to four oxygen (O) atoms. Recognizing the structure and charge of polyatomic ions is essential for understanding their role in chemical reactions and stoichiometry.
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Titration and Precipitation Reactions

Titration is a quantitative analytical method used to determine the concentration of a solute in a solution. In this scenario, the titration of AsO4^3- with Ag+ leads to the formation of a precipitate, Ag3AsO4. Understanding the principles of titration and precipitation reactions is crucial for analyzing the results and determining the amount of arsenic in the sample.
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Related Practice
Textbook Question

In 2014, a major chemical leak at a facility in West Virginia released 28,390 L of MCHM (4-methylcyclohexylmethanol, C8H16O) into the Elk River. The density of MCHM is 0.9074 g/mL. (a) Calculate the initial molarity of MCHM in the river, assuming that the first part of the river is 2.00 m deep, 90.0 m wide, and 90.0 m long.

Textbook Question
Ritalin is the trade name of a drug, methylphenidate, used to treat attention-deficit/hyperactivity disorder in young adults. The chemical structure of methylphenidate is (c) Ritalin has a half-life of 3 hours in the blood, which means that after 3 hours the concentration in the blood has decreased by half of its initial value. For the man in part (b), what is the concentration of Ritalin in his blood after 6 hours?
Textbook Question

The arsenic in a 1.22-g sample of a pesticide was converted to AsO43- by suitable chemical treatment. It was then titrated using Ag+ to form Ag3AsO4 as a precipitate. (b) Name Ag3AsO4 by analogy to the corresponding compound containing phosphorus in place of arsenic.

Textbook Question

The arsenic in a 1.22-g sample of a pesticide was converted to AsO43- by suitable chemical treatment. It was then titrated using Ag+ to form Ag3AsO4 as a precipitate. (c) If it took 25.0 mL of 0.102 M Ag+ to reach the equivalence point in this titration, what is the mass percentage of arsenic in the pesticide?