Question

If aqueous solutions of potassium chromate and barium chloride are mixed, a bright yellow solid (barium chromate) forms and settles 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 aqueous solutions of potassium chromate and barium chloride to form barium chromate and potassium chloride is: \[ \text{K}_2\text{CrO}_4(aq) + \text{BaCl}_2(aq) \to \text{BaCrO}_4(s) + 2\text{KCl}(aq) \]

Step-by-step solution

Write the unbalanced chemical equation.

Write down the chemical formulas of the reactants and products involved in the reaction. Reactants: - Potassium chromate (K2CrO4) - Barium chloride (BaCl2) Products: - Barium chromate (BaCrO4) - Potassium chloride (KCl) The unbalanced chemical equation is given by: K2CrO4(aq) + BaCl2(aq) -> BaCrO4(s) + KCl(aq)

Identify the ions in the equation.

Before balancing the equation, it is helpful to identify the ions involved in the reaction. The ions are as follows: - Potassium ion (K+) - Chromate ion (CrO4^2-) - Barium ion (Ba^2+) - Chloride ion (Cl-)

Balance the equation.

Adjust the coefficients of the reactants and products to ensure the same number of atoms for each element on both sides. K2CrO4(aq) + BaCl2(aq) -> BaCrO4(s) + KCl(aq) Looking at the equation, it becomes clear that we need two potassium ions (K+) and two chloride ions (Cl-) on the product side. So, we add a coefficient of 2 to KCl, giving: K2CrO4(aq) + BaCl2(aq) -> BaCrO4(s) + 2KCl(aq) We now have a balanced chemical equation for the reaction between potassium chromate and barium chloride: \[ \text{K}_2\text{CrO}_4(aq) + \text{BaCl}_2(aq) \to \text{BaCrO}_4(s) + 2\text{KCl}(aq) \] This equation shows that when aqueous solutions of potassium chromate and barium chloride are mixed, barium chromate (a yellow solid) and potassium chloride form.

Key concepts

Chemical Reaction

When studying chemistry, one fundamental concept we encounter is a chemical reaction. A chemical reaction is a process where substances, called reactants, transform into new substances called products. During this transformation, the atoms of the original substances rearrange, forming new compounds while conserving mass.

To identify a chemical reaction, we often look for visual signs such as color change, gas production, formation of a solid (precipitate), or temperature change. In the given exercise, the chemical reaction takes place between aqueous solutions of potassium chromate and barium chloride, resulting in the formation of a bright yellow solid, barium chromate, and a new solution of potassium chloride. This change is evident by the sudden appearance of the yellow precipitate—a clear sign that a chemical reaction has occurred.

Stoichiometry

To understand the quantitative aspect of chemical reactions, we turn to stoichiometry. This branch of chemistry is concerned with the calculation of relative quantities of reactants and products in chemical reactions. Stoichiometry is founded on the law of conservation of mass, which states that mass is neither created nor destroyed during a chemical reaction.

In our example, the exercise requires us to write a balanced chemical equation—a critical step in stoichiometry. A balanced equation has equal numbers of each type of atom on both sides of the reaction equation, reflecting the conservation of mass. Balancing equations involves adjusting coefficients, which are numbers placed before the chemical formulas to indicate the ratio of moles of each substance involved. Through correct stoichiometry, we can predict the amount of products formed from given reactants in the correct proportions. Balancing the equation for the given reaction not only teaches us how to apply stoichiometry but also allows us to better understand the reaction itself.

Precipitation Reaction

A key type of chemical reaction demonstrated in this exercise is a precipitation reaction. This occurs when two soluble substances react to form one or more insoluble products, called precipitates, which settle out from the reaction mixture. The process often results in a solid forming in a previously clear solution.

In the case of mixing potassium chromate and barium chloride, the precipitation reaction forms barium chromate, a yellow solid. This reaction is typical when a solution containing a metal cation reacts with another solution containing an anion to form an insoluble salt. Precipitation reactions are not only vital for the study of chemistry but also have practical applications in water treatment, mineral extraction, and the manufacturing of pigments, among other industries.