Problem 43 - Chemistry The Central Science In Si Units

Question

Magnesium carbonate, magnesium oxide, and magnesium hydroxide are all white solids that react with acidic solutions. (a) Write a balanced molecular equation and a net ionic equation for the reaction that occurs when each substance reacts with a hydrochloric acid solution. (b) By observing the reactions in part (a), how could you distinguish any of the three magnesium substances from the other two?

Step-by-Step Solution

Answer

Magnesium carbonate can be distinguished by the fizzing it produces when reacting with HCl, unlike magnesium oxide and magnesium hydroxide.

Step 1: Identify the Reactants

We need to determine the reactants involved in these reactions. All three substances mentioned (magnesium carbonate \(\text{MgCO}_3\), magnesium oxide \(\text{MgO}\), and magnesium hydroxide \(\text{Mg(OH)}_2\)) will react with hydrochloric acid (\(\text{HCl}\)).

Step 2: Write the Balanced Molecular Equations

The reactions are as follows: 1. Magnesium carbonate with HCl: \[ \text{MgCO}_3 (s) + 2\text{HCl} (aq) \rightarrow \text{MgCl}_2 (aq) + \text{CO}_2 (g) + \text{H}_2\text{O} (l) \]2. Magnesium oxide with HCl: \[ \text{MgO} (s) + 2\text{HCl} (aq) \rightarrow \text{MgCl}_2 (aq) + \text{H}_2\text{O} (l) \]3. Magnesium hydroxide with HCl: \[ \text{Mg(OH)}_2 (s) + 2\text{HCl} (aq) \rightarrow \text{MgCl}_2 (aq) + 2\text{H}_2\text{O} (l) \]

Step 3: Write the Net Ionic Equations

1. For magnesium carbonate: \[ \text{CO}_3^{2-} (s) + 2\text{H}^+ (aq) \rightarrow \text{CO}_2 (g) + \text{H}_2\text{O} (l) \]2. For magnesium oxide: \[ \text{O}^{2-} (s) + 2\text{H}^+ (aq) \rightarrow \text{H}_2\text{O} (l) \]3. For magnesium hydroxide: \[ \text{Mg(OH)}_2(s) \rightarrow \text{Mg}^{2+}(aq) + 2\text{OH}^{-} \] then \[ 2\text{OH}^- (s) + 2\text{H}^+ (aq) \rightarrow 2\text{H}_2\text{O} (l) \]

Step 4: Determine Observable Differences

Magnesium carbonate's reaction produces carbon dioxide gas, which will cause bubbling or fizzing. Magnesium oxide and magnesium hydroxide do not produce gases when reacting with \(\text{HCl}\). This fizzing can help distinguish magnesium carbonate from the other two.

Key Concepts

Magnesium Compounds

Magnesium compounds, such as magnesium carbonate (\(\text{MgCO}_3\)), magnesium oxide (\(\text{MgO}\)), and magnesium hydroxide (\(\text{Mg(OH)}_2\)), are commonly used in various chemical and industrial applications. Each of these compounds reacts uniquely with acidic solutions, such as hydrochloric acid (\(\text{HCl}\)).
The reactions showcase some typical behaviors of magnesium compounds when they interact with acids.

• **Magnesium Carbonate (\(\text{MgCO}_3\))**: This compound releases carbon dioxide gas when reacting with an acid, resulting in visible effervescence or fizzing.
• **Magnesium Oxide (\(\text{MgO}\))**: This reacts with acids to form magnesium chloride and water, with no gas production.
• **Magnesium Hydroxide (\(\text{Mg(OH)}_2\))**: It dissolves in acid, forming water and contributing magnesium ions to the solution.

Understanding these compounds' reactions is essential in the study of acid-base chemistry.

Balanced Chemical Equations

In chemistry, balanced chemical equations are crucial for representing what happens during a chemical reaction. They show the reactants transforming into products, maintaining the law of conservation of mass. When dealing with reactions involving magnesium compounds and hydrochloric acid, it is important to ensure that both sides of the equation have equal numbers of each type of atom.
Let's see how this works for magnesium compounds:

• **Magnesium Carbonate**: \( \text{MgCO}_3 (s) + 2\text{HCl} (aq) \rightarrow \text{MgCl}_2 (aq) + \text{CO}_2 (g) + \text{H}_2\text{O} (l) \)
• **Magnesium Oxide**: \( \text{MgO} (s) + 2\text{HCl} (aq) \rightarrow \text{MgCl}_2 (aq) + \text{H}_2\text{O} (l) \)
• **Magnesium Hydroxide**: \( \text{Mg(OH)}_2 (s) + 2\text{HCl} (aq) \rightarrow \text{MgCl}_2 (aq) + 2\text{H}_2\text{O} (l) \)

Balancing these equations ensures that the same amount of mass is present before and after the reaction, which is a fundamental principle in chemical reactions.

Net Ionic Equations

Net ionic equations focus on the ions that participate directly in the chemical reaction, excluding the spectator ions, which do not change during the process. These equations help in understanding the actual reacting species and the changes occurring at the molecular level.
Here are the net ionic equations for the reactions with magnesium compounds and hydrochloric acid:

• **Magnesium Carbonate**: \( \text{CO}_3^{2-} (s) + 2\text{H}^+ (aq) \rightarrow \text{CO}_2 (g) + \text{H}_2\text{O} (l) \)
• **Magnesium Oxide**: \( \text{O}^{2-} (s) + 2\text{H}^+ (aq) \rightarrow \text{H}_2\text{O} (l) \)
• **Magnesium Hydroxide**: The initial dissociation is \( \text{Mg(OH)}_2(s) \rightarrow \text{Mg}^{2+}(aq) + 2\text{OH}^- \), then \( 2\text{OH}^- (s) + 2\text{H}^+ (aq) \rightarrow 2\text{H}_2\text{O} (l) \)

Studying net ionic equations sharpens the understanding of which ions are truly involved in the reaction.

Reaction Observations

Observing reactions can provide valuable insights into the chemical processes occurring, especially when distinguishing similar substances. Magnesium carbonate, magnesium oxide, and magnesium hydroxide show different observable behaviors when reacting with a strong acid like hydrochloric acid (\(\text{HCl}\)).
Here's a summary of what you might see:

• **Magnesium Carbonate**: The reaction produces carbon dioxide gas, resulting in visible bubbles and fizzing.
• **Magnesium Oxide**: There is no gas produced, so this reaction appears calm, producing only a color change as the solution forms.
• **Magnesium Hydroxide**: Similar to \(\text{MgO}\), there is no bubbling; instead, the \(\text{Mg(OH)}_2\) dissolves to form a clear solution.

The differences in these observable reactions can help identify which magnesium compound you are dealing with based on visible signs like gas production or dissolution.