Problem 57 - Chemistry: Structure and Properties

Question

One of the key components in the manufacture of Portland cement is Ca3SiO5, a compound that is obtained by firing the reactants in a kiln at 1400-1500 C. Assign an oxidation state to each element in this compound.

Step-by-Step Solution

Answer

For the compound Ca3SiO5, Calcium (Ca) has an oxidation state of +2, Silicon (Si) has an oxidation state of +4, and Oxygen (O) has an oxidation state of -2.

Step 1: Understanding Oxidation States

Oxidation states are numbers assigned to elements in a chemical compound that reflect the number of electrons lost or gained by atoms of that element within the compound. For ionic compounds, this is often equal to the charge on the ions. The sum of oxidation states for all atoms in a neutral compound must equal zero.

Step 2: Assigning Oxidation State to Oxygen

In most compounds, oxygen has an oxidation state of -2. Assuming that there are no peroxides or superoxides in the compound, we can assign an oxidation state of -2 to each oxygen atom.

Step 3: Calculating the Total Oxidation State Contribution from Oxygen

Since there are five oxygen atoms each with an oxidation state of -2, the total oxidation state contributed by oxygen is -2 * 5 = -10.

Step 4: Assigning Oxidation State to Calcium

Calcium is a group 2 element and typically has an oxidation state of +2 in its compounds.

Step 5: Determining the Oxidation State of Silicon

To make the overall charge of the compound zero, we can calculate the oxidation state of silicon. Letting x be the oxidation state of silicon and knowing there are three calcium atoms, the total oxidation number from calcium is 3 * +2 = +6. The sum of the oxidation states should be zero, so +6 (from calcium) + x (from silicon) -10 (from oxygen) = 0. Solving for x gives x = +4.

Key Concepts

Understanding Oxidation States

Grasping the concept of oxidation states is fundamental in chemistry, especially when evaluating chemical reactions and compounds. Oxidation states, often referred to as oxidation numbers, provide us with a count of the electrons an atom might gain, lose, or share when forming chemical bonds. It's a hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic.

When assigning oxidation states, several rules can guide us:

• The oxidation state of a pure element is always zero.
• In most compounds, hydrogen has an oxidation state of +1, and oxygen has an oxidation state of -2.
• The sum of all oxidation states in a neutral molecule must be zero; in a polyatomic ion, it must equal the ion's charge.

Understanding these rules helps in balancing redox reactions, where the change in oxidation states indicates electron transfer between species.

Exploring Chemical Compounds

Chemical compounds are substances composed of two or more different types of atoms bonded together. These bonds can be covalent, where atoms share electrons, or ionic, where one atom donates electrons to another. The resulting compound exhibits properties that are distinct from its constituent elements.

In the case of Ca₃SiO₅, this is a compound crucial in the creation of Portland cement. It's an intriguing mixture because it contains both a metal (calcium) and a non-metal (silicon) bonded with oxygen. This particular arrangement of atoms within the compound reveals much about the nature of the bonds and their corresponding oxidation states, which is crucial in understanding the compound's behavior during the cement-making process.

Chemical Reactions and Cement Formation

Chemical reactions are the processes where reactants transform into products through breaking and re-forming chemical bonds. They are the heart of chemical synthesis, including the formation of compounds like Ca₃SiO₅ present in Portland cement.

The high-temperature conditions in a kiln needed to produce this compound result in the specific bonding and oxidation states observed. Chemical reactions involved in making cement are complex and involve significant energy input to produce these materials, emphasizing the importance of understanding both the underlying atomic interactions and the practical processes by which chemical compounds are synthesized.