Question

If aqueous solutions of potassium chromate and barium chloride are mixed, a bright yellow solid (barium chromate) forms and settle out of the mixture, leaving potassium chloride in solution. Write a balanced chemical equation for this process.

Short answer

The balanced chemical equation for the reaction between potassium chromate (K₂CrO₄) and barium chloride (BaCl₂) to form solid barium chromate (BaCrO₄) and potassium chloride (KCl) in solution is: \( K_2CrO_4(aq) + BaCl_2(aq) \rightarrow BaCrO_4(s) + 2KCl(aq) \).

Step-by-step solution

1) Write down the chemical formulas of the compounds involved in the reaction.

For each compound, use their respective ions: - Potassium chromate: Potassium ion (K⁺) and chromate ion (CrO₄²⁻). Therefore, its formula is K₂CrO₄. - Barium chloride: Barium ion (Ba²⁺) and chloride ion (Cl⁻). Hence, its formula is BaCl₂. - Barium chromate: Barium ion (Ba²⁺) and chromate ion (CrO₄²⁻). Thus, its formula is BaCrO₄. - Potassium chloride: Potassium ion (K⁺) and chloride ion (Cl⁻). So, its formula is KCl.

2) Write the unbalanced chemical equation.

Combine the reactants (potassium chromate and barium chloride) and the products (barium chromate and potassium chloride) to form the unbalanced equation: \( K_2CrO_4(aq) + BaCl_2(aq) \rightarrow BaCrO_4(s) + KCl(aq) \)

3) Balance the chemical equation.

Count the number of atoms of each element on both sides of the equation and balance them accordingly: - K: There are 2 K atoms on the left side and 1 K atom on the right side. So, we put a coefficient of 2 in front of KCl on the right side. \( K_2CrO_4(aq) + BaCl_2(aq) \rightarrow BaCrO_4(s) + 2KCl(aq) \) - Cl: There are 2 Cl atoms on the left side and 2x1=2 Cl atoms on the right side. The Cl atoms are balanced. - Ba and CrO4 ions are already balanced. The balanced chemical equation is: \( K_2CrO_4(aq) + BaCl_2(aq) \rightarrow BaCrO_4(s) + 2KCl(aq) \)

Key concepts

Balanced Chemical Equation

A balanced chemical equation is crucial for accurately representing a chemical reaction. It ensures the law of conservation of mass is followed, meaning atoms are neither created nor destroyed in the reaction. For the given exercise, your main task is to balance the equation for the reaction between potassium chromate and barium chloride.

First, identify the compounds involved and their chemical formulas:

• Potassium chromate: \( K_2CrO_4 \)
• Barium chloride: \( BaCl_2 \)
• Barium chromate: \( BaCrO_4 \)
• Potassium chloride: \( KCl \)

Once the unbalanced equation \( K_2CrO_4(aq) + BaCl_2(aq) \rightarrow BaCrO_4(s) + KCl(aq) \) is written, you need to ensure that the same number of each type of atom appears on both sides of the equation. Start by adjusting the coefficients. With a coefficient of 2 in front of \( KCl \), the final balanced equation becomes \( K_2CrO_4(aq) + BaCl_2(aq) \rightarrow BaCrO_4(s) + 2KCl(aq) \).

Balancing the equation is vital as it reflects the actual stoichiometry of the reaction, guiding the proportions needed for the reaction to occur efficiently.

Precipitation Reaction

A precipitation reaction occurs when two solutions are combined, resulting in the formation of an insoluble solid, known as a precipitate. In the exercise example, mixing aqueous solutions of potassium chromate and barium chloride leads to the formation of a bright yellow precipitate, barium chromate (\( BaCrO_4 \)).

This type of reaction is common in chemistry and is used to demonstrate the outcome of combining soluble ionic compounds that produce an insoluble product.

• Reactants: Potassium chromate and barium chloride are both soluble in water, meaning they dissolve to form ions.
• Product/Precipitate: Barium chromate does not dissolve in water, thus separating out as a solid.

Watching a precipitation reaction can visually help illustrate the principles of solubility and the interaction between different ions in a solution.

Ionic Compounds

Ionic compounds are composed of positively charged ions (cations) and negatively charged ions (anions). They form when atoms transfer electrons, resulting in a stable electrical configuration. The exercise provides an excellent example of how ionic compounds participate in reactions.

For each compound in the reaction:

• Potassium chromate: Contains potassium ions \( (K^+) \) and chromate ions \( (CrO_4^{2-}) \).
• Barium chloride: Comprises barium ions \( (Ba^{2+}) \) and chloride ions \( (Cl^-) \).
• Barium chromate: Consists of barium ions \( (Ba^{2+}) \) and chromate ions \( (CrO_4^{2-}) \), forming an insoluble compound.
• Potassium chloride: Has potassium ions \( (K^+) \) and chloride ions \( (Cl^-) \), which remain in solution after the reaction.

These compounds dissolve in water by dissociating into their respective ions, a crucial feature in understanding the behavior of solutions in chemical reactions such as precipitation. Ionic compounds are fundamental in various chemical processes and are characterized by their high melting and boiling points, conductivity when dissolved in a solution, and typically forming crystalline solids.