Problem 97 - Chemistry and Chemical Reactivity

Question

Describe how to prepare \(\mathrm{BaSO}_{4}\), barium sulfate, by (a) a precipitation reaction and (b) a gas-forming reaction. The available starting materials are \(\mathrm{BaCl}_{2}\) \(\mathrm{BaCO}_{3}, \mathrm{Ba}(\mathrm{OH})_{2}, \mathrm{H}_{2} \mathrm{SO}_{4},\) and \(\mathrm{Na}_{2} \mathrm{SO}_{4} .\) Write complete, balanced equations for the reactions chosen. (See page 138 for an illustration of the preparation of the compound.)

Step-by-Step Solution

Answer

Use \(\mathrm{BaCl}_{2}\) and \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) for precipitation; \(\mathrm{BaCO}_{3}\) and \(\mathrm{H}_{2}\mathrm{SO}_{4}\) for gas-forming, forming \(\mathrm{BaSO}_{4}\).

Step 1: Understanding Precipitation Reaction

A precipitation reaction occurs when two solutions combine to form an insoluble solid. In this case, we are looking to form barium sulfate, which is insoluble in water.

Step 2: Choosing Reactants for Precipitation

We need two solutions that contain barium and sulfate ions. The available starting materials give us options such as \(\mathrm{BaCl}_{2}\) and \(\mathrm{Na}_{2} \mathrm{SO}_{4}\). Combining these will result in the precipitation of \(\mathrm{BaSO}_{4}\).

Step 3: Writing Balanced Precipitation Reaction Equation

Combine \(\mathrm{BaCl}_{2}\) and \(\mathrm{Na}_{2}\mathrm{SO}_{4}\) in aqueous solution: \[ \mathrm{BaCl}_{2} (aq) + \mathrm{Na}_{2} \mathrm{SO}_{4} (aq) \rightarrow \mathrm{BaSO}_{4} (s) + 2 \mathrm{NaCl} (aq) \] This equation shows the formation of solid \(\mathrm{BaSO}_{4}\) as a precipitate.

Step 4: Introducing Gas-forming Reaction

A gas-forming reaction involves reactants that produce a gas as part of the reaction process. For forming \(\mathrm{BaSO}_{4}\), we will use \(\mathrm{BaCO}_{3}\) and \(\mathrm{H}_{2}\mathrm{SO}_{4}\).

Step 5: Writing Balanced Gas-forming Reaction Equation

Combine \(\mathrm{BaCO}_{3}\) with \(\mathrm{H}_{2} \mathrm{SO}_{4}\): \[ \mathrm{BaCO}_{3} (s) + \mathrm{H}_{2} \mathrm{SO}_{4} (aq) \rightarrow \mathrm{BaSO}_{4} (s) + \mathrm{CO}_{2} (g) + \mathrm{H}_{2} \mathrm{O} (l) \] This equation shows that \(\mathrm{BaSO}_{4}\) is formed along with \(\mathrm{CO}_{2}\) gas and water.

Key Concepts

Precipitation Reaction

A precipitation reaction occurs when two aqueous solutions combine, resulting in the formation of an insoluble solid called a precipitate. In the context of preparing barium sulfate (BaSO₄), a precipitation reaction is a straightforward and efficient method.

When barium chloride (\(\text{BaCl}_2\) ) and sodium sulfate (\(\text{Na}_2\text{SO}_4\) ) are dissolved in water, they dissociate into their respective ions, barium (Ba²⁺) and sulfate (SO₄²⁻).

Upon mixing these solutions, barium ions combine with sulfate ions to form barium sulfate, an insoluble compound that precipitates out of the solution. This is why it's often used in laboratory settings to prepare pure BaSO₄.

• Solubility rules are crucial here: \(\text{BaSO}_4\) is one of the few barium compounds that do not dissolve in water.
• This reaction not only forms BaSO₄ but also produces sodium chloride (NaCl), which remains dissolved as ions in the solution.

The balanced chemical equation for this precipitation reaction is:
\[\text{BaCl}_2 \text{(aq)} + \text{Na}_2\text{SO}_4 \text{(aq)} \rightarrow \text{BaSO}_4 \text{(s)} + 2 \text{NaCl} \text{(aq)}\] This simplified representation shows clearly how the ions rearrange themselves during the reaction.

Gas-forming Reaction

Gas-forming reactions are characterized by the production of a gaseous product during the reaction process. One effective way to prepare barium sulfate (\(\text{BaSO}_4\) ) through this method involves using barium carbonate (\(\text{BaCO}_3\) ) and sulfuric acid (\(\text{H}_2\text{SO}_4\) ).

The reaction between these two substances is not only practical but also illustrative of how gas-evolving reactions work. As \(\text{H}_2\text{SO}_4\) reacts with \(\text{BaCO}_3\) , a decomposition occurs where barium sulfate forms as a solid precipitate.

• Moreover, carbon dioxide (\(\text{CO}_2\) ) gas is released during this reaction.
• Water (\(\text{H}_2\text{O}\) ) is also a by-product, demonstrating the diversity of chemical species generated.

The balanced chemical equation for the reaction is:
\[\text{BaCO}_3 \text{(s)} + \text{H}_2\text{SO}_4 \text{(aq)} \rightarrow \text{BaSO}_4 \text{(s)} + \text{CO}_2 \text{(g)} + \text{H}_2\text{O} \text{(l)}\] This equation illustrates the transformation of solid \(\text{BaCO}_3\) into solid \(\text{BaSO}_4\) while also generating gaseous \(\text{CO}_2\) , highlighting the dynamic nature of gas-forming reactions.

Chemical Equation Balancing

Balancing chemical equations is an essential skill in chemistry that ensures the law of conservation of mass is upheld—it guarantees that matter is neither created nor destroyed.

In the preparation of barium sulfate (\(\text{BaSO}_4\) ), balancing the chemical equations for both precipitation and gas-forming reactions involves making sure the number of each type of atom is the same on both sides of the equation.

• Precipitation Reaction:
  \[\text{BaCl}_2 \text{(aq)} + \text{Na}_2\text{SO}_4 \text{(aq)} \rightarrow \text{BaSO}_4 \text{(s)} + 2 \text{NaCl} \text{(aq)}\]
• Gas-forming Reaction:
  \[\text{BaCO}_3 \text{(s)} + \text{H}_2\text{SO}_4 \text{(aq)} \rightarrow \text{BaSO}_4 \text{(s)} + \text{CO}_2 \text{(g)} + \text{H}_2\text{O} \text{(l)}\]

Each reaction is a good example of how equations are balanced:

The cations and anions must balance out their charges and the types of atoms need to be equal on both sides.

In the \(\text{BaCl}_2\) and \(\text{Na}_2\text{SO}_4\) reaction, two Na⁺ ions are balanced by the two Cl⁻ ions formed.

Meanwhile, the \(\text{CO}_2\) gas formed in the \(\text{BaCO}_3\) reaction reflects a careful balancing of oxygen, carbon, and hydrogen.

Understanding these fundamentals makes predicting and analyzing chemical reactions easier, providing a foundation for deeper exploration into chemistry.