Problem 88 - Chemistry and Chemical Reactivity

Question

You want to prepare barium chloride, \(\mathrm{BaCl}_{2},\) using an exchange reaction of some type. To do so, you have the following reagents from which to select the reactants: \(\mathrm{BaSO}_{4}, \mathrm{BaBr}_{2}, \mathrm{BaCO}_{3}, \mathrm{Ba}(\mathrm{OH})_{2}, \mathrm{HCl}, \mathrm{HgSO}_{4}, \mathrm{AgNO}_{3}\) and HNO \(_{3} .\) Write a complete, balanced equation for the reaction chosen. (Note: There are several possibilities.)

Step-by-Step Solution

Answer

Use \(\mathrm{Ba(OH)}_{2}\) and \(\mathrm{HCl}\) to form \(\mathrm{BaCl}_{2}\), balanced as: \(\mathrm{Ba(OH)}_{2} + 2\mathrm{HCl} \rightarrow \mathrm{BaCl}_{2} + 2\mathrm{H_2O}\).

Step 1: Identify Possible Reactants

To form Barium Chloride (\(\mathrm{BaCl}_{2}\)), we need a source of Barium (\(\mathrm{Ba^{2+}}\)) and a source of Chloride (\(\mathrm{Cl^{-}}\)). From the given reagents, \(\mathrm{HCl}\) can provide \(\mathrm{Cl^{-}}\). Possible sources of \(\mathrm{Ba^{2+}}\) include \(\mathrm{BaSO}_{4}\), \(\mathrm{BaBr}_{2}\), \(\mathrm{BaCO}_{3}\), and \(\mathrm{Ba(OH)}_{2}\).

Step 2: Consider the Exchange Reaction

In an exchange reaction, also known as a double displacement reaction, the cations and anions of the reactants switch places, forming two new compounds. To form \(\mathrm{BaCl}_{2}\), we need to choose a barium-containing compound that will react with \(\mathrm{HCl}\).

Step 3: Choose Suitable Reactants

Choose \(\mathrm{Ba(OH)}_{2}\) as it can react with \(\mathrm{HCl}\) to easily release \(\mathrm{Ba^{2+}}\) and form \(\mathrm{BaCl}_{2}\) in an aqueous solution. The balanced reaction will produce barium chloride and water.

Step 4: Write the Balanced Equation

The balanced chemical equation using \(\mathrm{Ba(OH)}_{2}\) and \(\mathrm{HCl}\) is:\[\mathrm{Ba(OH)}_{2} + 2\mathrm{HCl} \rightarrow \mathrm{BaCl}_{2} + 2\mathrm{H_2O}\]

Step 5: Verify the Balance and Products

Ensure that the reaction is balanced by checking that the number of each type of atom is equal on both sides of the equation. The products \(\mathrm{BaCl}_{2}\) and \(\mathrm{H_2O}\) match the required product and a common by-product (water) for such a reaction.

Key Concepts

Barium Chloride Preparation

Barium chloride, represented as \(\mathrm{BaCl}_{2}\), is commonly prepared through a chemical process known as an exchange reaction. This compound is vital in various laboratory and industrial applications due to its properties. To prepare barium chloride, you need to combine a barium compound with a source of chloride ions. It is crucial to choose reactants that will allow for a clean and efficient reaction.
In our example, the reactants were chosen from a list including compounds like \(\mathrm{HCl}\) and \(\mathrm{Ba(OH)}_{2}\). By selecting these, we ensure that the exchange reaction leads to the desired compound of barium chloride along with water as a byproduct.

Balanced Equation

Chemical reactions need to be expressed through balanced equations to satisfy the law of conservation of mass. This means the number of each type of atom must be the same on both sides of the reaction equation.
For the preparation of barium chloride, the chosen balanced equation is:\[\mathrm{Ba(OH)}_{2} + 2\mathrm{HCl} \rightarrow \mathrm{BaCl}_{2} + 2\mathrm{H_2O}\]
This equation tells us that one molecule of barium hydroxide reacts with two molecules of hydrochloric acid to produce one molecule of barium chloride and two molecules of water. Carefully checking this balance ensures no atom is lost or gained, maintaining equilibrium.

Exchange Reaction

An exchange reaction, often referred to as a double displacement reaction, involves the swapping of ions between two compounds, resulting in the formation of two different compounds. In the reaction to create barium chloride, \(\mathrm{Ba(OH)}_{2}\) and \(\mathrm{HCl}\) serve as the reactants.

• The barium ion \(\mathrm{Ba^{2+}}\) from \(\mathrm{Ba(OH)}_{2}\) pairs with the chloride ions \(\mathrm{Cl^{-}}\) from \(\mathrm{HCl}\).
• Meanwhile, the \(\mathrm{H}^{+}\) from \(\mathrm{HCl}\) combines with the hydroxide ions \(\mathrm{OH^{-}}\) from \(\mathrm{Ba(OH)}_{2}\) to form water, \(\mathrm{H_2O}\).

This switch of partners is the hallmark of exchange or double displacement reactions, allowing for the transformation into desired products like barium chloride.

Double Displacement Reaction

A double displacement or exchange reaction involves two reactants exchanging components to generate two new products. For producing barium chloride, the reaction where \(\mathrm{Ba(OH)}_{2}\) combines with \(\mathrm{HCl}\) perfectly depicts this type of reaction.
Here's what transpires:

• The barium ions \(\mathrm{Ba^{2+}}\) from the first reactant switch places with the hydrogen ions \(\mathrm{H^{+}}\) from the second reactant.
• This swap results in the formation of \(\mathrm{BaCl}_{2}\) and \(\mathrm{H_2O}\).

This balanced transformation is what makes double displacement reactions so useful for synthesis in chemistry.

Reactant Selection

Choosing the correct reactants for a chemical preparation involves careful consideration of the compounds' properties and how they interact in a reaction. For barium chloride synthesis, several barium-containing compounds are possible, but not all will react effectively with \(\mathrm{HCl}\), our source of chloride ions.
Among potential candidates, \(\mathrm{Ba(OH)}_{2}\) is selected due to its readiness to react with \(\mathrm{HCl}\) to form \(\mathrm{BaCl}_{2}\) efficiently. It works because it can donate \(\mathrm{Ba^{2+}}\) ions with minimal byproducts other than water, ensuring a clean reaction. This highlights the importance of reactant choice in achieving desired reaction outcomes.