Problem 123 - Chemistry and Chemical Reactivity

Question

Describe how to prepare BaSO, barium sulfate, by (a) a precipitation reaction and (b) a gas-forming reaction. To do so, you have the following reagents from which to select the reactants: \(\mathrm{BaCl}_{2}, \mathrm{BaCO}_{3}, \mathrm{Ba}(\mathrm{OH})_{2}, \mathrm{H}_{2} \mathrm{SO}_{4},\) and \(\mathrm{Na}_{2} \mathrm{SO}_{4} .\) Write complete, balanced equations for the reactions chosen. (See Figure 4.8 for an illustration of the preparation of a compound.)

Step-by-Step Solution

Answer

Precipitation: BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl; Gas-forming: BaCO₃ + H₂SO₄ → BaSO₄ + H₂O + CO₂.

Step 1: Identify Precipitation Reaction

A precipitation reaction involves mixing two solutions to form an insoluble solid, called a precipitate. For barium sulfate (BaSO₄), this occurs when a barium-containing compound reacts with a sulfate-containing compound. Based on the given reagents, we can use barium chloride (BaCl₂) and sodium sulfate (Na₂SO₄).

Step 2: Write Balanced Precipitation Reaction Equation

Combine the barium chloride and sodium sulfate to form barium sulfate and sodium chloride. The balanced chemical equation is: \[\text{BaCl}_2 (aq) + \text{Na}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + 2\text{NaCl} (aq)\] Here, BaSO₄ is the precipitate.

Step 3: Identify Gas-Forming Reaction

A gas-forming reaction may involve a carbon dioxide or other gas being produced alongside the compound we want. Barium carbonate (BaCO₃) and sulfuric acid (H₂SO₄) can react to form barium sulfate, water, and carbon dioxide gas.

Step 4: Write Balanced Gas-Forming Reaction Equation

Combine barium carbonate with sulfuric acid. The balanced chemical equation is:\[\text{BaCO}_3 (s) + \text{H}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + \text{H}_2\text{O} (l) + \text{CO}_2 (g)\]In this reaction, carbon dioxide gas is evolved.

Key Concepts

Precipitation Reaction

A precipitation reaction is a type of chemical reaction where two solutions are combined, and an insoluble solid, known as a precipitate, forms. This occurs when certain ions in the solution join together to create a compound that is not soluble in the liquid and settles out.

In the context of preparing barium sulfate (BaSO₄), we can achieve this by mixing a barium-containing compound with a sulfate-containing compound. From the reagents provided, barium chloride (BaCl₂) and sodium sulfate (Na₂SO₄) serve as the ideal reactants.

The chemical reaction that occurs is represented by the following balanced equation: \[\text{BaCl}_2 (aq) + \text{Na}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + 2\text{NaCl} (aq)\] Here, barium sulfate precipitates out from the solution as an insoluble solid, making it the compound of interest. Notice how both sides of the equation have the same number of each type of atom, ensuring it is balanced.

Gas-Forming Reaction

A gas-forming reaction is a fascinating process where a gas is produced as one of the products when the reactants interact. Often in gas-forming reactions, either carbon dioxide (CO₂) or another gas is released. These reactions can lead to observable bubbling or effervescence as the gas escapes from the liquid.

To prepare barium sulfate through a gas-forming reaction, barium carbonate (BaCO₃) and sulfuric acid (H₂SO₄) are excellent choices from the given reagents. When these two substances react, barium sulfate, water, and carbon dioxide gas are created. The balanced chemical equation for this reaction is: \[\text{BaCO}_3 (s) + \text{H}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + \text{H}_2\text{O} (l) + \text{CO}_2 (g)\] As the reaction proceeds, carbon dioxide gas is liberated, which might be observed as bubbles or fizzing in the mixture. Notably, barium sulfate remains as the insoluble precipitate, completing the desired chemical formation.

Balanced Chemical Equation

A balanced chemical equation is a representation of a chemical reaction where the number of atoms for each element is the same on both sides of the equation. This balance is crucial because it reflects the conservation of mass, indicating that no atoms are lost or gained during the reaction.

Balancing equations involves adjusting the coefficients, which are the numbers before the chemical symbols, to ensure that the count of each kind of atom is equal on both sides. For example, in our precipitation reaction equation: \[\text{BaCl}_2 (aq) + \text{Na}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + 2\text{NaCl} (aq)\] We check to see that there are the same number of barium, sulfate, sodium, and chloride ions before and after the reaction takes place.

Similarly, in the gas-forming reaction: \[\text{BaCO}_3 (s) + \text{H}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + \text{H}_2\text{O} (l) + \text{CO}_2 (g)\] The amounts of barium, carbon, oxygen, hydrogen, and sulfur are equal on each side, maintaining the principle of mass conservation. Balancing is essential for accurately describing a chemical reaction and its outcomes.