Problem 10 - Chemistry: The Central Science in SI Units, Global Edition

Question

A key step in balancing chemical equations is correctly identifying the formulas of the reactants and products. For example, consider the reaction between calcium oxide, \(\mathrm{CaO}(s)\) and \(\mathrm{H}_{2} \mathrm{O}(l)\) to form aqueous calcium hydroxide. (a) Write a balanced chemical equation for this combination reaction, having correctly identified the product as \(\mathrm{Ca}(\mathrm{OH})_{2}(a q)\) (b) Is it possible to balance the equation if you incorrectly identify the product as \(\mathrm{CaOH}(a q)\), and if so, what is the equation?

Step-by-Step Solution

Answer

The balanced chemical equation for the reaction between calcium oxide (CaO) and water (H2O) to produce aqueous calcium hydroxide (Ca(OH)2) is: \(CaO(s) + H_2 O(l) \rightarrow Ca(OH)_2(aq) \). It is not possible to balance the equation with the incorrect product CaOH(aq), because it leads to unbalanced number of atoms for Calcium.

Step 1: (a) Identify Reactants and Products

The given reactants are: 1. Calcium oxide: CaO(s) 2. Water: H2O(l) The given product is: 1. Aqueous calcium hydroxide: Ca(OH)2(aq) Now, we will balance the chemical equation.

Step 2: (a) Balance the Chemical Equation

In order to balance the chemical equation, we need to make sure that the number of atoms of each element is equal on both sides of the equation. Initial unbalanced equation: CaO(s) + H2O(l) -> Ca(OH)2(aq) We can see that the number of atoms for each element is equal on both sides, so the balanced equation is: \(CaO(s) + H_2 O(l) \rightarrow Ca(OH)_2(aq)\)

Step 3: (b) Incorrect Identification of Product

In this part, we will consider the product as CaOH(aq) instead of Ca(OH)2. Let's try to balance the equation.

Step 4: (b) Balance the Incorrect Equation

Unbalanced equation with the incorrect product: CaO(s) + H2O(l) -> CaOH(aq) Balancing this equation, we find that it's impossible to balance properly, since any equal number of Oxygen and Hydrogen will also lead to Calcium being unbalanced. Therefore, it is not possible to balance the equation with the incorrect product CaOH(aq).

Key Concepts

Chemical Formulas

Chemical formulas are the symbolic representation of atoms in a chemical compound. Each element is identified by its chemical symbol and the number of atoms of each element is indicated by a subscript (if more than one). For example, in calcium oxide, \(\mathrm{CaO}(s)\), there is one calcium atom and one oxygen atom bonded together.

• Symbols: Stand for the elements (e.g., Ca for Calcium).
• Subscripts: Indicate the number of atoms (e.g., the "2" in \(\mathrm{H_{2}O}\) indicates two hydrogen atoms).
• Parentheses: Used in complex ions or groups (e.g., \(\mathrm{OH}\) hydroxide in \(\mathrm{Ca(OH)_2}\)).

The correct formula includes all necessary atoms and represents the composition of the compounds accurately. Misidentifying any compound will lead to errors in chemical reactions and unbalance the equation as seen in the example when you mix up \(\mathrm{Ca(OH)_{2}}\) and \(\mathrm{CaOH}\). Ensuring accuracy in chemical formulas is fundamental to balancing equations correctly.

Reactants and Products

In any chemical reaction, reactants are substances you start with, and products are what you end up with. Reactants and products are always involved in a chemical equation representing the process. With the example of calcium oxide and water reacting, your reactants are:

• Calcium Oxide: \(\mathrm{CaO}(s)\)
• Water: \(\mathrm{H_{2}O}(l)\)

And your product is:

• Aqueous Calcium Hydroxide: \(\mathrm{Ca(OH)_{2}}(aq)\)

To confirm a reaction, you must ensure the equation is balanced. Balancing involves making sure the number of each type of atom on the reactant side equals the corresponding number on the product side. In this case, both sides of the equation have equal numbers of calcium, oxygen, and hydrogen atoms.If identified or written incorrectly, the products such as \(\mathrm{CaOH}\) rather than \(\mathrm{Ca(OH)_{2}}\) result in an unbalanced equation and highlight the importance of correct formulas.

Aqueous Calcium Hydroxide

Aqueous calcium hydroxide is an industrially significant compound, often used in various applications like water treatment and construction. Aqueous indicates that the compound is dissolved in water, denoted by \(\text{(aq)}\). This state affects how substances react, often making them more active in a liquid solution than in solid form.

• Formula: \(\mathrm{Ca(OH)_{2}}(aq)\) comprises calcium, oxygen, and hydrogen atoms.
• Uses: Provides chemical bases in laboratories, serves in neutralizing acidic substances.

The balance shown in the reaction \(\mathrm{CaO}(s) + \mathrm{H_{2}O}(l) \rightarrow \mathrm{Ca(OH)_{2}}(aq)\) demonstrates how reactants transform into this useful product. It shows how balanced equations help reflect the conservation of mass principle, proving that matter cannot be created or destroyed. Remember, accurate chemical identification is crucial in portraying real-world reactions and processes.