Question

Describe how to prepare \(\mathrm{BaSO}_{4},\) 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 page 127 for an illustration of the preparation of a compound.)

Short answer

Use \(\text{BaCl}_2\) and \(\text{Na}_2\text{SO}_4\) for precipitation; \(\text{BaCO}_3\) and \(\text{H}_2\text{SO}_4\) for gas formation.

Step-by-step solution

Understanding Precipitation Reaction Formula

In a precipitation reaction, two soluble salts interact in an aqueous solution to form an insoluble product, a precipitate. To prepare barium sulfate (\(\text{BaSO}_4\)) using this method, we can combine \(\text{BaCl}_2\) with \(\text{Na}_2\text{SO}_4\). The reaction is: \(\text{BaCl}_2 (aq) + \text{Na}_2\text{SO}_4(aq) \rightarrow \text{BaSO}_4(s) + 2\text{NaCl}(aq)\).

Balancing Precipitation Reaction Equation

The equation balances with each type of atom present in equal numbers on both sides. The sulfate and barium ions interact to form \(\text{BaSO}_4\), which precipitates out of the solution as a solid.

Choosing Reagents for Gas-forming Reaction

A gas-forming reaction typically involves an acid and a carbonate compound, resulting in the formation of a gas, water, and a salt. We will use \(\text{BaCO}_3\) and \(\text{H}_2\text{SO}_4\) to initiate this reaction.

Writing Balanced Gas-forming Reaction Equation

The balanced equation for the reaction is: \(\text{BaCO}_3 (s) + \text{H}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + \text{CO}_2 (g) + \text{H}_2\text{O} (l)\). Here, \(\text{BaSO}_4\) is formed as a solid, and carbon dioxide gas is released.

Key concepts

Precipitation Reaction

In chemistry, a precipitation reaction occurs when two soluble salts are mixed in an aqueous solution, resulting in the formation of an insoluble product known as a precipitate. This type of reaction is a fundamental concept in chemistry because it allows us to isolate specific compounds. To illustrate this, let's consider the preparation of barium sulfate (\(\text{BaSO}_4\)) by a precipitation reaction.

When soluble \(\text{BaCl}_2\) (barium chloride) reacts with \(\text{Na}_2\text{SO}_4\) (sodium sulfate), the result is the formation of barium sulfate and sodium chloride. Here is the balanced chemical equation for this reaction:

• \(\text{BaCl}_2 (aq) + \text{Na}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + 2\text{NaCl} (aq)\)

The key product, barium sulfate, forms as a solid and precipitates out of the solution, while sodium chloride remains dissolved. This type of reaction is particularly valuable in various industrial and laboratory settings where separation and purification of substances are required.

Gas-forming Reaction

A gas-forming reaction is another intriguing process, where a reaction yields a gas as one of the products. A common way to create a gas-forming reaction is to mix an acid with a carbonate. In our context, we can utilize this process to generate barium sulfate along with a gaseous byproduct.

By combining barium carbonate (\(\text{BaCO}_3\)) with sulfuric acid (\(\text{H}_2\text{SO}_4\)), a chemical reaction occurs that forms barium sulfate, carbon dioxide gas, and water. The following equation demonstrates this reaction:

• \(\text{BaCO}_3 (s) + \text{H}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + \text{CO}_2 (g) + \text{H}_2\text{O} (l)\)

In this reaction, carbon dioxide is the gas that forms and is released as a byproduct, resulting in the visible effervescence as the reaction proceeds. This makes gas-forming reactions quite interesting to watch and study.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions. These expressions not only show the starting materials (reactants) and what they transform into (products) but also ensure that the mass balance follows the law of conservation of matter. That means the same number of each type of atom must appear on both sides of the equation.

To achieve this mass balance, we write "balanced" equations by adjusting coefficients, not subscripts. For example, the precipitation reaction forming barium sulfate is balanced as shown:

• \(\text{BaCl}_2 (aq) + \text{Na}_2\text{SO}_4 (aq) \rightarrow \text{BaSO}_4 (s) + 2\text{NaCl} (aq)\)

This balance ensures that we have an equal number of barium, sulfate, sodium, and chloride ions before and after the reaction.

The importance of correctly writing and balancing chemical equations cannot be overstated, as they are crucial for predicting the outcomes and yields of chemical reactions, which is fundamental in both industrial applications and classroom learning.

Barium Compounds

Barium compounds play a pivotal role in various chemical processes and are significant in numerous industrial applications. One of the best-known barium compounds is barium sulfate (\(\text{BaSO}_4\)), appreciated for its high density and opacity.

Here are some interesting facts:

• Barium sulfate is often used in medical imaging as a radiocontrast agent for X-rays and CT scans due to its opacity to X-ray radiation.
• In industrial terms, it is utilized as a filler in plastics, rubber, and resins because of its inertness and good dispersion properties.

Other barium compounds, such as barium chloride (\(\text{BaCl}_2\)) and barium carbonate (\(\text{BaCO}_3\)), are also significant. Barium chloride serves as a source for the preparation of other barium compounds, while barium carbonate is valuable in the glass and ceramics industries.

Understanding the use and reactivity of barium compounds allows chemists to harness their properties appropriately across different fields, from healthcare to manufacturing.