Question

On the basis of the general solubility rules given in Table \(7.1,\) predict the identity of the precipitate that forms when aqueous solutions of the following substances are mixed. If no precipitate is likely, indicate which rules apply.

Short answer

Based on the general solubility rules, we can determine if precipitates form when mixing aqueous solutions of given substances A and B by following these steps: 1. Write the complete ionic equation representing the mixing of aqueous solutions of A and B. 2. Apply solubility rules to determine if the products, AB and A₂B₂, will form a precipitate (a solid). 3. Identify the precipitate that forms, or indicate the solubility rules that apply if no precipitate forms. For example, if we mix aqueous solutions of A and B, we write the complete ionic equation as: A⁺(aq) + A₂(aq) + B⁻(aq) + B₂(aq) → AB(aq/s) + A₂B₂(aq/s) Based on solubility rules, we can determine if AB or A₂B₂ will form a precipitate or remain soluble. If a precipitate forms, we identify the compound; otherwise, we mention the solubility rules that apply.

Step-by-step solution

Write the chemical reaction

Write the complete ionic equation representing the mixing of aqueous solutions of A and B. We'll represent the ions as A⁺, A₂, B⁻, and B₂ based on their charge. The possible products are AB and A₂B₂. A⁺(aq) + A₂(aq) + B⁻(aq) + B₂(aq) → AB(aq/s) + A₂B₂(aq/s) In this equation, (aq/s) represents that the compound can be in aqueous or solid state, depending on the solubility.

Apply solubility rules

Check the solubility rules to determine if the products, AB and A₂B₂, will form a precipitate (a solid). Below are some general solubility rules: 1. All Group 1 (alkali metals) and ammonium (NH₄⁺) compounds are soluble. 2. Nitrates (NO₃⁻), acetates (CH₃COO⁻), and most perchlorates (ClO₄⁻) are soluble. 3. Halides (Cl⁻, Br⁻, I⁻) are soluble, except when combined with silver (Ag⁺), mercury(I) (Hg₂⁺²), or lead (Pb²⁺). 4. Most sulfates (SO₄²⁻) are soluble, except when combined with Sr²⁺, Ba²⁺, Ra²⁺, or Pb²⁺. 5. Most hydroxides (OH⁻) are insoluble, except when combined with Group 1 elements or Ca²⁺, Sr²⁺, and Ba²⁺. 6. Carbonates (CO₃²⁻), phosphates (PO₄³⁻), chromates (CrO₄²⁻), and sulfides (S²⁻) are generally insoluble, except when combined with Group 1 elements or ammonium.

Determine if precipitates form

Based on the solubility rules, if any of the products AB or A₂B₂ have low solubility, they will form a solid and precipitate. If both are soluble, no precipitate forms and the rules that apply should be mentioned.

Identify the precipitate or rules applied

If a precipitate forms, identify the compound as the precipitate. If no precipitate forms, mention the solubility rules that apply to the given substances. This step-by-step approach can be applied to any example problem involving precipitation of compounds and solubility rules.

Key concepts

Precipitation Reactions

Precipitation reactions occur when two aqueous solutions are combined and an insoluble solid, known as a precipitate, forms and falls out of the solution. The process involves mixing ionic compounds; sometimes the cations and anions will combine to form compounds that are not soluble in water, leading to the formation of a solid.

When an equation for a potential precipitation reaction is written, all reactants should be listed as ions if they are soluble. During the reaction, you observe which ions are attracted to each other and can form a new compound. This new compound must be insoluble according to solubility rules for it to precipitate.

In determining if a precipitate is formed, the complete ionic equation can be helpful. This equation shows both the charges and states (solid or aqueous) of the compounds involved. Identifying precipitates accurately requires consultation of a solubility chart, which tells you whether a compound remains in solution or forms a solid.

Solubility of Compounds

The solubility of compounds is key in deciding whether a precipitate will form in a reaction. Solubility rules provide guidelines that help predict whether an ionic compound is soluble or insoluble in water. Generally, compounds like nitrates, acetates, and many sulfates dissolve well in water. Conversely, compounds such as carbonates, phosphates, and most sulfides tend to be insoluble unless combined with specific ions like Group 1 elements or ammonium.

Understanding solubility is important because soluble compounds remain dissolved, meaning that no precipitate will form, while insoluble compounds result in a solid precipitate. This is why, in practice, mixing solutions requires checking if the resultant matter is soluble through these rules.

These rules are empirical, meaning they are based on experimental observations rather than theory. However, they are proven to be reliable and are widely used to predict the outcomes of mixing aqueous chemical solutions.

Chemical Reactions in Aqueous Solutions

Chemical reactions in aqueous solutions involve reactants dissolved in water, which allows ions to move freely and react to form products. The aqueous environment facilitates the breaking and forming of ionic bonds as reactants collide and combine in new ways. Converting a chemical equation into its ionic form is essential to understand the states of reactants before concluding the reaction's outcome.

In aqueous solutions, whether a reaction leads to the formation of a precipitate depends on the solubility of the potential products. Solubility rules determine if a product is stable in its dissolved state or if it will form a solid precipitate.

These types of reactions are common in both natural systems and laboratories, where they are used to isolate particular substances or to study reaction kinetics. Knowing how substances behave in water can predict reaction mechanisms and products, making solubility rules an invaluable tool in chemistry.