Problem 68 - Chemistry: The Central Science in SI Units, Global Edition

Question

Write a balanced equation for each of the following reactions: (a) Burning magnesium metal in a carbon dioxide atmosphere reduces the \(\mathrm{CO}_{2}\) to carbon. (b) \(\mathrm{In}\) photosynthesis, solar energy is used to produce glucose \(\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right)\) and \(\mathrm{O}_{2}\) from carbon dioxide and water. (c) When carbonate salts dissolve in water, they produce basic solutions.

Step-by-Step Solution

Answer

(a) Mg + CO2 -> MgO + C (b) 6CO2 + 6H2O -> C6H12O6 + 6O2 (c) MCO3 -> M(OH)2 + CO2

Step 1: Write the unbalanced equation.

Write down the reactants and products for the given reaction: Mg + CO2 -> MgO + C

Step 2: Balance the equation.

We need to make sure there is the same number of each element on both sides of the equation. To balance the equation, we can multiply any of the compounds by some coefficients. The balanced equation is: Mg + CO2 -> MgO + C For reaction (b):

Step 1: Write the unbalanced equation.

Write down the reactants and products for the given reaction: CO2 + H2O -> C6H12O6 + O2

Step 2: Balance the equation.

We need to make sure there is the same number of each element on both sides of the equation. To balance the equation, we can multiply any of the compounds by some coefficients. The balanced equation is: 6CO2 + 6H2O -> C6H12O6 + 6O2 For reaction (c):

Step 1: Write the general reaction.

Carbonate salts generally dissolve in water and produce hydroxide, or OH- ions. Since the formula of a carbonate salt is MCO3, where M is a metal cation, we can write down the general half-reaction: MCO3 -> MOH + CO2

Step 2: Determine the coefficients.

We need to make sure there is the same number of each element on both sides of the reaction. Considering that the coefficient for the hydroxide ion (OH-) is 2, the balanced half-equation is: MCO3 -> M(OH)2 + CO2 Note that this is a general balanced equation for when carbonate salts dissolve in water and produce basic solutions.

Key Concepts

Balancing Reactions

Balancing chemical equations is an essential skill in chemistry. It ensures that the same number of atoms for each element is present on both sides of the equation. This reflects the law of conservation of mass, which states that mass cannot be created or destroyed during a chemical reaction.
To balance a reaction, follow these steps:

• Write down the unbalanced equation with the correct chemical formulas for all reactants and products.
• Check the number of atoms of each element on both sides of the equation.
• Adjust the coefficients, which are numbers placed before compounds, to ensure that each element has the same number of atoms on both sides.

Let's take the example of magnesium burning in a carbon dioxide atmosphere:

• Unbalanced equation: \( \text{Mg} + \text{CO}_2 \rightarrow \text{MgO} + \text{C} \)
• Balanced equation: \( \text{2Mg} + \text{CO}_2 \rightarrow \text{2MgO} + \text{C} \)

This balanced equation shows that 2 magnesium atoms react with 1 carbon dioxide molecule to produce 2 magnesium oxide compounds and 1 carbon atom. Balancing chemical reactions is like solving a puzzle where each piece must fit perfectly, ensuring that no atoms are lost or gained.

Photosynthesis Chemical Reaction

Photosynthesis is a fascinating process used by plants to convert light energy into chemical energy. This happens in the form of glucose, a sugar molecule. The overall reaction of photosynthesis involves carbon dioxide and water as reactants that produce glucose and oxygen.
The general form of the photosynthesis chemical reaction is:

• Unbalanced equation: \( \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + \text{O}_2 \)
• Balanced equation: \( 6\text{CO}_2 + 6\text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \)

In this balanced equation, the light energy from the sun allows 6 molecules of carbon dioxide and 6 molecules of water to convert into 1 molecule of glucose and 6 molecules of oxygen.
Photosynthesis not only provides energy for plants but also releases oxygen into the atmosphere, which is essential for the survival of most life forms on Earth. The balanced photosynthesis equation perfectly exemplifies nature's efficiency in energy conversion.

Solubility and Basic Solutions

Solubility refers to how well a substance dissolves in a solvent, in this case, water. When discussing carbonate salts, this involves forming basic solutions when they dissolve. A basic solution means one that contains more hydroxide ions \((\text{OH}^-\)) compared to hydrogen ions \((\text{H}^+\)).
When carbonate salts dissolve in water, they typically form metal hydroxides and release carbon dioxide gas:

• General reaction: \( \text{MCO}_3 \rightarrow \text{MOH} + \text{CO}_2 \)
• Balanced reaction: \( \text{MCO}_3 \rightarrow \text{M(OH)}_2 + \text{CO}_2 \)

In this case, \( \text{M} \) represents a metal cation that balances the charge in the compound. The formation of \( \text{OH}^- \) ions from dissolving carbonate salts leads to a solution with a higher pH, making it basic.
A key concept to understand is that when carbonate salts dissolve, they undergo a chemical transformation that affects the solution's pH. This process is fundamentally based on the particular carbonate's ability to dissociate and form these alkaline products, highlighting its role in natural and industrial processes such as water softening and pH regulation.