Problem 69 - Chemistry and Chemical Reactivity

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

Step-by-Step Solution

Answer

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

Step 1: Identify soluble compound with bromide ion

Choose a commonly known soluble compound that contains the bromide ion. Sodium bromide (NaBr) is often used because sodium salts are generally soluble and bromide is a halide, which is commonly soluble.

Step 2: Identify an insoluble hydroxide

Select a metal hydroxide that is known to be insoluble in water. An appropriate example is Iron(III) hydroxide, Fe(OH)₃, which is insoluble.

Step 3: Identify an insoluble carbonate

Choose a carbonate that typically does not dissolve in water. Calcium carbonate, CaCO₃, is a well-known example of an insoluble carbonate.

Step 4: Identify a soluble nitrate-containing compound

Pick a compound that includes the nitrate ion, as nitrates are almost always soluble. Potassium nitrate, KNO₃, is a suitable example.

Step 5: Identify a weak Bronsted acid

Select an acid that does not completely dissociate in solution, classifying it as a weak acid. Acetic acid, CH₃COOH, is a common weak Bronsted acid.

Key Concepts

Solubility Rules

When it comes to defining whether a compound dissolves in water, solubility rules serve as a clever guideline. They help predict the behavior of ions in water, which is important for chemistry students. Here's a glance at some basic rules that often apply:

• Most nitrate (NO₃⁻) salts are soluble, meaning they dissolve well in water.
• Ammonium (NH₄⁺) salts and alkali metal salts, like those of sodium (Na⁺) and potassium (K⁺), are typically soluble.
• Halides such as chlorides (Cl⁻), bromides (Br⁻), and iodides (I⁻) are mostly soluble, except when paired with silver (Ag⁺), lead (Pb²⁺), and mercury (Hg₂²⁺).
• Most carbonates (CO₃²⁻) and hydroxides (OH⁻) are insoluble, with exceptions including alkali metals and ammonium hydroxide.

These rules are like a handy guide in your backpack during chemistry class, helping you predict the solubility of common compounds.

Bronsted Acids

Bronsted acids are fascinating because they focus on the transfer of protons. According to the Bronsted-Lowry theory, an acid is a proton donor—in simple terms, it gives away a hydrogen ion (H⁺) to form its conjugate base.
Acids can be **strong** or **weak**:

• Strong acids like hydrochloric acid (HCl) completely dissociate in water, releasing their protons.
• Weak acids, such as acetic acid (CH₃COOH), only partially dissociate. This means not all their protons are released, giving them a lower impact on the pH of a solution.

Understanding whether an acid is strong or weak is useful because it affects how they behave in chemical reactions. Remember, in aqueous solutions, water plays a role as a base, accepting hydrogen ions, and completes the acidic reaction.

Chemical Formulas

Chemical formulas are a symbolic language of chemistry, representing the elements within compounds and their respective ratios. They provide a lot of information at just a glance.
Formulas are formatted with element symbols, and subscripts are used to show the number of each type of atom.

• Take Sodium bromide (NaBr). "Na" is for sodium, and "Br" is for bromide, reflecting a 1:1 ratio.
• Iron(III) hydroxide (Fe(OH)₃) has iron combined with three hydroxide (OH⁻) ions.

To interpret these formulas:

• Identify each element by its chemical symbol.
• Use subscripts to determine how many atoms of each element are present.

Learning to read chemical formulas is like learning the alphabet of chemistry, unlocking insights into the makeup of compounds.

Compound Classification

Classifying chemical compounds helps chemists understand their properties and predict their behavior in reactions. Different categories of compounds are based on their chemical and physical properties.
**Insoluble Compounds**:

• Compounds like calcium carbonate (CaCO₃), which do not dissolve in water, are considered insoluble.
• Iron(III) hydroxide (Fe(OH)₃) is another example, forming a solid precipitate in aqueous solutions.

**Soluble Compounds**:

• Sodium bromide (NaBr) and potassium nitrate (KNO₃) readily dissolve in water, making them soluble.
• These compounds are used in solutions where ionic mobility is required.

Recognizing whether a compound is soluble or insoluble is critical in experiments, helping in tasks like precipitate formation or solution preparation.