Question

Write a chemical equation for the reaction of aqueous solutions of potassium chromate and calcium sulfate to give calcium chromate precipitate and aqueous potassium sulfate.

Short answer

The balanced chemical equation is: \( \text{K}_2\text{CrO}_4 (aq) + \text{CaSO}_4 (aq) \rightarrow \text{CaCrO}_4 (s) + \text{K}_2\text{SO}_4 (aq) \).

Step-by-step solution

Write the Chemical Formulas of Reactants

First, identify the chemical formulas of the reactants. Potassium chromate is written as \( \text{K}_2\text{CrO}_4 \), and calcium sulfate is written as \( \text{CaSO}_4 \). Both are in aqueous solution.

Write the Chemical Formulas of Products

Next, write the chemical formulas for the products. Calcium chromate, which precipitates, is written as \( \text{CaCrO}_4 \). Potassium sulfate, which remains in aqueous solution, is written as \( \text{K}_2\text{SO}_4 \).

Write the Unbalanced Chemical Equation

Now, write the unbalanced chemical equation showing the reactants and products: \[ \text{K}_2\text{CrO}_4 (aq) + \text{CaSO}_4 (aq) \rightarrow \text{CaCrO}_4 (s) + \text{K}_2\text{SO}_4 (aq) \]

Balance the Chemical Equation

Adjust the coefficients to balance the chemical equation. Each element must have the same number of atoms on both sides. The balanced chemical equation is: \[ \text{K}_2\text{CrO}_4 (aq) + \text{CaSO}_4 (aq) \rightarrow \text{CaCrO}_4 (s) + \text{K}_2\text{SO}_4 (aq) \] The equation is already balanced as written because there are equal counts of each type of atom on both sides.

Key concepts

Reactants and Products

When considering a chemical reaction, it is essential to identify the reactants and products. Reactants are substances that undergo a chemical change, and they appear on the left side of the chemical equation. In this case, the reactants are potassium chromate (\( \text{K}_2\text{CrO}_4 \)) and calcium sulfate (\( \text{CaSO}_4 \)).
Products are the substances generated from the reaction, shown on the right side of the equation. For this particular reaction, the products are calcium chromate (\( \text{CaCrO}_4 \)), which is a solid precipitate, and potassium sulfate (\( \text{K}_2\text{SO}_4 \)), which remains aqueous. Each chemical formula is like a recipe detailing the elements and their ratios.

• Reactants: Starting materials in a reaction, e.g., \( \text{K}_2\text{CrO}_4 \) and \( \text{CaSO}_4 \).
• Products: Resulting materials from a reaction, e.g., \( \text{CaCrO}_4 \) and \( \text{K}_2\text{SO}_4 \).
• The transition from reactants to products involves rearrangements of atoms.

Balancing Equations

Balancing chemical equations ensures that the same number of each type of atom appears on both sides of the equation.
This reflects the fundamental principle of the conservation of mass, which states that mass cannot be created or destroyed in a chemical reaction.
To balance an equation, adjust the coefficients—the numbers in front of molecules—so that atom counts for each element are equal.
Let's examine:\[ \text{K}_2\text{CrO}_4 (aq) + \text{CaSO}_4 (aq) \rightarrow \text{CaCrO}_4 (s) + \text{K}_2\text{SO}_4 (aq) \]

• This equation is balanced as each element has an equal number of atoms on both sides. No coefficients need changing.
• Understanding that each molecule contains specific atoms helps in arranging necessary coefficients strategically.
• Proper balancing is crucial for accurate depiction of a chemical reaction, allowing predictions about how much of each reactant is needed and how much product can be formed.

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions mix to form an insoluble solid, known as a precipitate.
In this case, mixing potassium chromate and calcium sulfate results in calcium chromate as a precipitate.
In a precipitation reaction:

• The solid formed is the precipitate, seen on the product side of the equation as \( \text{CaCrO}_4 (s) \).
• These reactions are a type of double displacement reaction, where the ions switch places to form the solid product.
• Surface applications, including removing unwanted materials from solutions and various purification processes, benefit from precipitation reactions.

Understanding the solubility rules helps predict when a precipitation will occur, as not every combination of ions will result in a solid. It's these intricacies that make precipitation reactions fascinating and practically useful.