Assign oxidation numbers to each element in the following ions. (f) AsO4 3-

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Step 1: Understand that the sum of oxidation numbers in a polyatomic ion equals the charge of the ion. For AsO₄³⁻, the sum of oxidation numbers should equal -3.

Step 2: Assign the oxidation number for oxygen. Oxygen typically has an oxidation number of -2.

Step 3: Calculate the total oxidation number for all oxygen atoms. Since there are four oxygen atoms, multiply the oxidation number of one oxygen atom by four: 4(-2) = -8.

Step 4: Let the oxidation number of arsenic (As) be x. Set up the equation based on the sum of oxidation numbers: x + (-8) = -3.

Step 5: Solve the equation for x to find the oxidation number of arsenic. This will give you the oxidation number for arsenic in the ion.

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Key Concepts

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

Oxidation Numbers

Oxidation numbers are a way to keep track of electrons in chemical compounds. They indicate the degree of oxidation of an atom in a molecule, helping to determine how electrons are distributed among atoms. The oxidation number can be positive, negative, or zero, depending on the atom's electron gain or loss relative to its elemental state.

Rules for Assigning Oxidation Numbers

There are specific rules for assigning oxidation numbers, such as: the oxidation number of an element in its standard state is zero, the oxidation number of a monoatomic ion equals its charge, and in compounds, the sum of oxidation numbers must equal the overall charge of the molecule or ion. These rules provide a systematic approach to determine the oxidation states of each element in a compound.

Polyatomic Ions

Polyatomic ions are ions composed of two or more atoms that are covalently bonded and carry a net charge. In the case of AsO4 3-, the arsenate ion consists of one arsenic atom and four oxygen atoms, with a total charge of -3. Understanding the structure and charge of polyatomic ions is essential for correctly assigning oxidation numbers to their constituent elements.