Question

Which of the following statements is/are true regarding solutions? a. If a solute is dissolved in water, then the resulting solution is considered aqueous. b. If two solutions are mixed and no chemical reaction occurs, then a net ionic equation cannot be written. c. If two clear solutions are mixed and then cloudiness results, this indicates that a precipitate formed.

Short answer

Statements a, b, and c are all true. An aqueous solution results when a solute dissolves in water. A net ionic equation cannot be written if no chemical reaction occurs when mixing two solutions. Cloudiness appearing after mixing two clear solutions indicates the formation of a precipitate.

Step-by-step solution

Statement a

If a solute is dissolved in water, then the resulting solution is considered aqueous. This statement is true. By definition, an aqueous solution is a solution in which the solvent is water. So, when a solute is dissolved in water, the resulting mixture is an aqueous solution.

Statement b

If two solutions are mixed and no chemical reaction occurs, then a net ionic equation cannot be written. This statement is true. A net ionic equation represents the chemical species that participate in a reaction and change during the reaction. If there is no chemical reaction occurring when two solutions are mixed, then there are no changes happening in the chemical species, and thus, a net ionic equation cannot be written.

Statement c

If two clear solutions are mixed and then cloudiness results, this indicates that a precipitate formed. This statement is true. When two clear solutions are mixed, and a cloudiness appears, it is an indication of the formation of a solid substance, which is called a precipitate. This occurs when two soluble species react to form an insoluble product, and the insoluble product causes the cloudiness in the solution.

Key concepts

Solubility in Chemistry

Understanding solubility is foundational in studying chemical solutions. In simple terms, solubility refers to the maximum amount of solute that can dissolve in a solvent at a given temperature and pressure.

When we talk about an aqueous solution, we're referring to a solution where water acts as the solvent. Solutes—whether they be salts, sugars, gases, or other substances—have varying degrees of solubility in water. Factors affecting solubility include temperature, molecular structure, and the nature of the solvent. For instance, salts like sodium chloride (NaCl) are highly soluble in water, while gases like carbon dioxide (CO2) have lower solubility.

It's important to realize that solubility limits exist; when these are exceeded, the substance no longer dissolves and may form a precipitate, leading to a saturation point. This concept is critical when predicting the outcome of mixing different solutions, as seen in the textbook example, where the formation of a precipitate indicates reaching a solubility limit.

Net Ionic Equations

To fully grasp chemical reactions in aqueous solutions, knowing how to write net ionic equations is key. A net ionic equation breaks down the overall chemical equation into its ionic components, showing the actual chemical species that are changing during the reaction.

When writing a net ionic equation, you start with a balanced molecular equation, split the strong electrolytes into their ions, and then eliminate the spectator ions—those that do not participate in the actual chemical reaction. What remains are the ions that undergo a change, which can help you identify the driving force behind the reaction, such as the formation of a precipitate or a gas.

This elimination process results in a clearer understanding of the reaction's mechanism, making it easier to study and remember the reactions of interest. If no reaction occurs, as with the mixing of two solutions where all species remain unchanged, there's no net ionic equation to be written.

Precipitation Reactions

Precipitation reactions are essential processes that occur when two aqueous solutions combine to form an insoluble solid known as a precipitate. This type of reaction is typically represented by the appearance of cloudiness, as seen in the exercise's statement c.

During the course of a precipitation reaction, the reactants—usually two soluble salts—interact and produce at least one insoluble product. This product is what we refer to as a precipitate, and it will settle out of the solution due to its inability to dissolve in the solvent. A common example is the reaction between aqueous silver nitrate (AgNO3) and sodium chloride, which produces solid silver chloride (AgCl) as the precipitate.

Precipitation reactions are not only interesting from a theoretical standpoint but also have practical applications, including water treatment, qualitative chemical analysis, and the formation of geological features like stalactites and stalagmites. Recognizing and predicting these reactions are key skills in chemical studies.