Question

Give a formula for each of the following compounds: (a) a soluble compound containing the bromide ion (b) an insoluble hydroxide (c) an insoluble carbonate (d) a soluble nitrate-containing compound (e) a weak Bronsted acid

Short answer

(a) NaBr, (b) Fe(OH)₃, (c) CaCO₃, (d) KNO₃, (e) CH₃COOH

Step-by-step solution

Understanding Solubility and Ion Trends

To solve these questions, we need to recall solubility rules and the characteristics of acids and bases in chemistry. Solubility rules help us identify which compounds are soluble or insoluble in water based on the anion present in the compound. For Bronsted acids, we look at whether the compound is known to donate hydrogen ions weakly in a solution.

Finding a Soluble Bromide

According to solubility rules, bromides are generally soluble except when combined with certain metal ions like lead (Pb), silver (Ag), or mercury (Hg). Thus, a soluble bromide could be sodium bromide (NaBr) since sodium ions do not form exceptions with bromide anions.

Identifying an Insoluble Hydroxide

Most hydroxides are insoluble except those of alkali metals and barium (Ba). An example of an insoluble hydroxide is iron(III) hydroxide, Fe(OH)₃, which forms a precipitate and does not dissolve in water.

Selecting an Insoluble Carbonate

Carbonates are generally insoluble except those of alkali metals and ammonium. For example, calcium carbonate (CaCO₃) is insoluble in water and known to form precipitates.

Choosing a Soluble Nitrate

Nitrates are typically soluble in water regardless of the cation they are paired with. An example of a soluble nitrate is potassium nitrate (KNO₃).

Identifying a Weak Bronsted Acid

Weak acids only partially ionize in solution, and acetic acid (CH₃COOH) is a common weak Bronsted acid. It is known for its equilibrium between its ionized and un-ionized forms in solution.

Key concepts

Bronsted Acid

A Bronsted acid is a substance that can donate a hydrogen ion, or proton, to another substance. This ability to donate a proton makes it a central player in acid-base chemistry. However, not all acids are created equal. Some are strong and completely dissociate in water, while others, like acetic acid, are weak and only partially dissociate. Weak acids, such as acetic acid, do not fully donate all the protons to the solution, which means the reverse reaction, where the acid reforms, is also significant. Understanding Bronsted acids is crucial because they are common in many chemical reactions, particularly in biological systems and industrial processes. For example:

• They play a role in digestion, where hydrochloric acid in the stomach aids in breaking down food.
• In industry, sulfuric acid is used in the manufacture of fertilizers and other chemicals.

By learning about Bronsted acids, students gain insights into fundamental acid-base interactions.

Soluble vs Insoluble Compounds

Determining whether a compound is soluble or insoluble in water is essential for predicting reactions in aqueous solutions. Solubility rules provide guidelines based on the type of ions present, which help predict whether a compound will dissolve in water. These rules suggest that:

• Most nitrates ( NO₃⁻ ) are soluble and will dissolve regardless of the cation present.
• Alkali metal ions, like sodium (Na⁺) and potassium (K⁺), tend to form soluble compounds.
• Halides such as chlorides, bromides, and iodides are generally soluble, but there are exceptions with ions like lead, mercury, and silver.

On the other hand, compounds such as carbonates (CO₃²⁻) and phosphates are typically insoluble, except for those of alkali metals and ammonium. Understanding which compounds are soluble or insoluble helps in predicting if a product will precipitate in a reaction.

Chemical Formulas

Chemical formulas are abbreviated ways to indicate the composition of a compound. They show which elements are involved and in what proportion. In formulas like NaBr , each element is represented by its chemical symbol, and the numbers indicate the ratio of atoms. For instance:

• NaBr (Sodium Bromide) shows a 1:1 ratio of sodium to bromide ions.
• Fe(OH)₃ (Iron(III) Hydroxide) suggests there are three hydroxide ions per iron ion.

Understanding chemical formulas is critical, as it helps articulate the balance required in chemical reactions. For students, practicing reading and writing these formulas is key to mastering chemistry.

Ion Trends

Ion trends describe how different ions behave and interact with one another in solutions. Understanding these trends aids in making predictions about reaction outcomes. For example:

• Cations like sodium (Na⁺) and potassium (K⁺) are often associated with water-soluble compounds due to their stable, single-positive charges.
• Network-forming anions (e.g., CO₃²⁻ and PO₄³⁻ ) tend to be involved in the formation of insoluble compounds due to their higher negative charges and larger size, which can form strong lattice structures.

Ion trends can significantly impact the properties of a compound, influencing factors like solubility, electrical conductivity, and chemical reactivity. Grasping these concepts prepares students to understand the dynamic nature of chemical solutions.

Acid-Base Chemistry

Acid-base chemistry is a branch of chemistry that deals with the principles of how acids and bases interact, neutralize each other, and affect pH levels in solutions.Acids, like the Bronsted acids, donate protons while bases accept them. This interaction can be described by chemical equations that highlight the exchange of hydrogen ions (H⁺). For example, in water:\[\text{{HA}} + \text{{H}}_2\text{{O}} \leftrightarrow \text{{H}}_3\text{{O}}^+ + \text{{A}}^-\]The hydronium ion (H₃O⁺) forms when an acid donates a proton to water.This acid-base knowledge is applied in various fields, from environmental science where it helps manage soil and water pH to everyday products like baking soda, which neutralizes acids. Understanding these reactions enriches students' knowledge of chemical equilibria and reaction dynamics.