Question

Assign oxidation states to all of the atoms in each of the following: a. ${\mathrm{MnO}}_2$ b. ${\mathrm{BaCrO}}_4$ C. ${\mathrm{H}}_2{\mathrm{SO}}_3$ d. ${\mathrm{Ca}}_3{\left({\mathrm{PO}}_4\right)}_2$

Short answer

The assigned oxidation states for the given compounds are as follows: a. MnO2: Mn(+4), O(-2) b. BaCrO4: Ba(+2), Cr(+6), O(-2) c. H2SO3: H(+1), S(+4), O(-2) d. Ca3(PO4)2: Ca(+2), P(+5), O(-2)

Step-by-step solution

Identify the known oxidation states

Oxygen has an oxidation state of -2.

Calculate the oxidation state for Mn

Since there are two oxygen atoms (each with an oxidation state of -2), their total oxidation state is -4. To follow rule 2, the oxidation state of Mn must be +4. Therefore, the oxidation states are Mn(+4) and O(-2). b. Assign oxidation states to BaCrO4

Identify the known oxidation states

Barium (Ba) has an oxidation state of +2, and oxygen has an oxidation state of -2.

Calculate the oxidation state for Cr

There are four oxygen atoms (each with an oxidation state of -2), so their total oxidation state is -8. The oxidation state of Ba is +2. Therefore, the oxidation state of Cr must be +6 to follow rule 2. The oxidation states are Ba(+2), Cr(+6), and O(-2). c. Assign oxidation states to H2SO3

Identify the known oxidation states

Hydrogen has an oxidation state of +1, and oxygen has an oxidation state of -2.

Calculate the oxidation state for S

There are two hydrogen atoms (each with an oxidation state of +1), so their total oxidation state is +2. There are three oxygen atoms (each with an oxidation state of -2), so their total oxidation state is -6. Therefore, the oxidation state of S must be +4 to follow rule 2. The oxidation states are H(+1), S(+4), and O(-2). d. Assign oxidation states to Ca3(PO4)2

Identify the known oxidation states

Calcium (Ca) has an oxidation state of +2, and oxygen has an oxidation state of -2.

Calculate the oxidation state for P

There are three calcium atoms (each with an oxidation state of +2), so their total oxidation state is +6. Additionally, there are eight oxygen atoms (each with an oxidation state of -2), so their total oxidation state is -16. In order to follow rule 2, the total oxidation states for two phosphorus atoms must balance this, equaling +10. Therefore, the oxidation state of P is +5. The oxidation states are Ca(+2), P(+5), and O(-2).

Key concepts

Assigning Oxidation Numbers

Understanding how to assign oxidation numbers is essential for mastering redox reactions. Oxidation numbers, also known as oxidation states, reflect the degree of oxidation or reduction of an atom within a compound. Here's a simplified guide on how to determine these numbers:

• Know the common rules - Certain elements have 'typical' oxidation states. Oxygen is usually -2 (except in peroxides), hydrogen is usually +1 (except in metal hydrides where it is -1), and alkali metals (in Group 1) are always +1 while alkaline earth metals (in Group 2) are always +2.
• Use the rules systematically - Start with known oxidation states and use them to determine the unknown ones. In compounds, the sum of all oxidation states must equal the charge of the compound (which is zero for neutral compounds).
• Consider structure - In polyatomic ions, the sum of oxidation states should equal the ion's charge. For example, in the sulfate ion (SO₄²⁻), sulfur has an oxidation state that balances out the -2 charge from the four oxygen atoms.

Once comfortable with these guidelines, practice by assigning oxidation numbers to various compounds, as in the textbook exercises. This not only aids in understanding chemical reactions but also sets a foundation for further exploration in redox chemistry.

Chemical Nomenclature

The language of chemistry includes the chemical nomenclature, which is the systematic naming of chemical compounds. It provides a clear and concise way for scientists to communicate about compounds and their reactions. Here are a few basics:

• Use of prefixes and suffixes - In ionic compounds, we often name the cation (positive ion) first, followed by the anion (negative ion). For molecular compounds, we use prefixes to indicate the number of atoms present (e.g., mono-, di-, tri-).
• Importance of oxidation states - When naming compounds with transition metals, it is crucial to indicate the oxidation state of the metal, as they can have multiple possible states. For example, FeCl₂ is named iron(II) chloride, while FeCl₃ is iron(III) chloride.
• Recognize functional groups - In organic chemistry, the nomenclature revolves around the functional groups within the molecules. Such groups define the properties and reactivity of the molecules.

By mastering chemical nomenclature, students can describe and discern between compounds easily, be they in a chemical equation or when conducting experiments in a lab setting.

Redox Reactions

Redox reactions are a fundamental part of chemistry involving the transfer of electrons between two species. These reactions are crucial for many processes, from electrochemical cells to metabolism in living organisms. Key points to understand include:

• Oxidation and Reduction - Oxidation is the loss of electrons, and reduction is the gain of electrons. Remember the mnemonic 'OIL RIG'—Oxidation Is Loss, Reduction Is Gain.
• Tracking electrons - Assigning oxidation numbers helps to track how electrons are transferred during a reaction. An increase in oxidation number means oxidation; a decrease means reduction.
• Redox couples - Redox reactions occur in pairs; for every oxidized species, there is a reduced counterpart. These are often termed redox couples.
• Electrochemical applications - In galvanic cells, a redox reaction produces an electric current, while in electrolytic cells, an electric current drives a non-spontaneous redox reaction.

Considering redox reactions offer insight into the reactivity and characteristics of different elements and compounds. They show us how certain reactions can generate electricity or how substances can be transformed at the molecular level.