Question

One of the key components in the manufacture of Portland cement is \(\mathrm{Ca}_{3} \mathrm{SiO}_{5}\), a compound that is obtained by firing the reactants in a kiln at \(1400-1500^{\circ} \mathrm{C}\). Assign an oxidation state to each element in this compound.

Short answer

In the compound \(\mathrm{Ca}_{3} \mathrm{SiO}_{5}\), the oxidation state of calcium (Ca) is +2, the oxidation state of silicon (Si) is +4, and the oxidation state of oxygen (O) is -2.

Step-by-step solution

Understand the Concept of Oxidation States

Oxidation states (also known as oxidation numbers) are a concept in chemistry that reflects the degree of oxidation of an atom in a chemical compound. Conventionally, the oxidation state of an element in its natural state or elemental form is zero.

Apply the Rules for Assigning Oxidation States

There are several rules for assigning oxidation states. Key rules include: Oxygen usually has an oxidation state of -2, except in peroxides or when bonded to fluorine, and Group 1 metals have an oxidation state of +1, while Group 2 metals have an oxidation state of +2.

Assign Oxidation State to Oxygen

According to the rules, oxygen in compounds typically has an oxidation state of -2. As there are five oxygen atoms in \(\mathrm{Ca}_{3} \mathrm{SiO}_{5}\), the total oxidation state for oxygen is \(5 \times -2 = -10\).

Assign Oxidation State to Calcium

Calcium is an alkaline earth metal from Group 2 and it generally has an oxidation state of +2. Since there are three calcium atoms in the compound, the total oxidation state for calcium is \(3 \times +2 = +6\).

Balance Oxidation States to Determine Silicon's Oxidation State

The compound must be electrically neutral. Therefore, the sum of oxidation states of all elements in it must equal zero. Let \(x\) be the oxidation state of silicon, then for one silicon atom: \(+6 + x + (-10) = 0\). Solving for \(x\) gives the oxidation state of silicon as: \(+4\), since \(+6 - 10 + x = 0\) implies \(x = +4\).

Key concepts

Assigning Oxidation Numbers

Understanding how to assign oxidation numbers is essential for students studying redox reactions and chemical compound formation. An oxidation number is a measure that indicates whether an atom is in a reduced or oxidized state within a molecule. To assign these numbers, chemists follow a set of rules. For example, the oxidation number of a pure element is always zero, meaning that no charge is associated with that atom when it's not in a compound. Likewise, for monoatomic ions, the oxidation number is the same as the ion's charge.

When dealing with molecules, certain rules tend to take precedence over others. For instance, oxygen typically has an oxidation number of -2, except in peroxides where it's -1 or when it's bonded to fluorine. Alkali metals like sodium and potassium possess an oxidation number of +1, while alkaline earth metals such as magnesium and calcium have an oxidation number of +2. Hydrogen is usually +1 when bonded to nonmetals and -1 with metals. By systematically applying these rules, students can deduce the oxidation state of any element in a compound, which is crucial for properly understanding chemical reactions and processes.

Chemical Compounds

A chemical compound consists of two or more different elements that are chemically bonded together. The structure of compounds determines their chemical properties and behavior during reactions. In the educational example \(\mathrm{Ca}_{3} \mathrm{SiO}_{5}\), known as calcium silicate, each element's oxidation number provides insight into the compound's chemical characteristics.

For a compound to be stable, it needs to be electrically neutral; the sum of the positive and negative charges must equal zero. Understanding how to combine elements with appropriate oxidation states can predict possible compounds' formation. Additionally, knowing the common oxidation states of particular elements can help with this prediction. For example, calcium typically has a +2 oxidation state, and oxygen usually has -2. This knowledge is fundamental in creating balanced chemical equations and in other areas of chemistry such as stoichiometry, which involves calculating the proportions of reactants and products in chemical reactions.

Balancing Oxidation States

In chemical compounds, balance is key, and this includes the oxidation states. To ensure that the compound is neutral, the sum of the oxidation numbers must equal zero. When we know the oxidation states of some elements in the compound, we can find the unknown values.

For instance, the calcium silicate example raises the question of silicon's oxidation state. With the oxidation states of calcium and oxygen known, silicon's oxidation number can be determined by balancing the total charges to zero. This method is critical for identifying unknown oxidation states in more complex molecules. In academic practice, this concept of balancing oxidation states is regularly teamed up with the law of conservation of mass to balance chemical equations, where both the number of atoms and the total charge must be the same on both sides of the equation. It's a fundamental exercise not only to understand chemical reactions but also to predict reaction products and to gain a deeper comprehension of the properties of elements within various oxidation states.