Problem 104 - Chemistry Matter and Change

Question

What type of reaction is the following? (Chapter 9) $$ \mathrm{K}_{2} \mathrm{CO}_{3}(\mathrm{aq})+\mathrm{BaCl}_{2}(\mathrm{aq}) \rightarrow 2 \mathrm{KCl}(\mathrm{aq})+\mathrm{BaCO}_{3}(\mathrm{s}) $$ $$ \begin{array}{ll}{\text { a. combustion }} & {\text { c. single-replacement }} \\\ {\text { b. double-replacement }} & {\text { d. synthesis }}\end{array} $$

Step-by-Step Solution

Answer

The reaction is a double-replacement reaction (option b).

Step 1: Identify the reactants and products

The given chemical equation is \( \mathrm{K}_{2} \mathrm{CO}_{3} (\mathrm{aq}) + \mathrm{BaCl}_{2} (\mathrm{aq}) \rightarrow 2 \mathrm{KCl} (\mathrm{aq}) + \mathrm{BaCO}_{3} (\mathrm{s}) \). Here, the reactants are aqueous solutions of potassium carbonate (\( \mathrm{K}_{2} \mathrm{CO}_{3} \)) and barium chloride (\( \mathrm{BaCl}_{2} \)). The products are aqueous potassium chloride (\( \mathrm{KCl} \)) and solid barium carbonate (\( \mathrm{BaCO}_{3} \)).

Step 2: Recognize the reaction pattern

Look at how the ions exchange in the reaction. Potassium (\( \mathrm{K}^{+} \)) from \( \mathrm{K}_{2} \mathrm{CO}_{3} \) pairs with chloride (\( \mathrm{Cl}^{-} \)) from \( \mathrm{BaCl}_{2} \), forming \( \mathrm{KCl} \). Similarly, barium (\( \mathrm{Ba}^{2+} \)) from \( \mathrm{BaCl}_{2} \) pairs with carbonate (\( \mathrm{CO}_{3}^{2-} \)) from \( \mathrm{K}_{2} \mathrm{CO}_{3} \), forming \( \mathrm{BaCO}_{3} \).

Step 3: Categorize the reaction type

This exchange of ions indicates a double-replacement reaction, where two compounds exchange partners to form two new compounds. Double-replacement reactions typically involve the formation of a precipitate, a gas, or a weak electrolyte.

Step 4: Match with given options

The choices provided for the type of reaction include combustion, double-replacement, single-replacement, and synthesis. Based on the exchange pattern of ions, the reaction matches the description of a 'double-replacement' reaction.

Key Concepts

Understanding Chemical Reactions

Chemical reactions involve the transformation of substances through the breaking and formation of chemical bonds. In a chemical reaction, reactants are transformed into products. This process involves rearranging atoms to create new substances with different properties. There are several types of chemical reactions, each with its unique pattern of atom rearrangement:

• Combustion Reactions: Involve substances reacting with oxygen to release energy, usually in the form of heat and light.
• Single-Replacement Reactions: An atom or ion in one compound is replaced by an atom or ion of another element.
• Double-Replacement Reactions: Two ionic compounds exchange ions to form two new compounds.
• Synthesis Reactions: Two or more simple substances combine to form a more complex compound.

In the given exercise, we're looking at a double-replacement reaction, which is distinguished by the exchange of ions resulting in new compound formation. This type of reaction often leads to the formation of a precipitate.

The Nature of Ionic Compounds

Ionic compounds are made up of positive and negative ions, which are held together by strong electrostatic forces. These compounds typically form between metals and non-metals. For example, in the given reaction:

• Potassium Carbonate (\(\mathrm{K}_{2} \mathrm{CO}_{3}\)) contains potassium ions \(\mathrm{K}^{+}\) and carbonate ions \(\mathrm{CO}_{3}^{2-}\).
• Barium Chloride (\(\mathrm{BaCl}_{2}\)) contains barium ions \(\mathrm{Ba}^{2+}\) and chloride ions \(\mathrm{Cl}^{-}\).

Ionic compounds dissolve in water and disassociate into their respective ions, allowing them to interact with other dissolved ions. In the double-replacement reaction, these ions shuffle partners to create new ionic compounds.

The Process of Precipitate Formation

Precipitate formation occurs when a double-replacement reaction results in an insoluble solid. In solution, ionic compounds are typically dissolved, but sometimes when new ions combine, they form a substance that does not dissolve in water. Dissolved ions recombine according to their charges and, if the new combination forms an insoluble compound, a precipitate results. For example, in the exercise reaction, the following precipitate is observed:

• Barium Carbonate (\(\mathrm{BaCO}_{3}\)) is the precipitate formed.

Barium carbonate is insoluble in water, causing it to settle out of the solution as a solid. This solidification marks the removal of some ions from the solution, which is a key characteristic of a successful double-replacement reaction producing a precipitate. Recognizing the formation of a precipitate is vital for determining the pathways and results of chemical reactions.