Question

What factors qualify a compound as a salt? Specify which of the following compounds are salts: \(\mathrm{CH}_{4},\) NaF, \(\mathrm{NaOH}, \mathrm{CaO}, \mathrm{BaSO}_{4}, \mathrm{HNO}_{3}, \mathrm{NH}_{3}, \mathrm{KBr}\)

Short answer

NaF, BaSO₄, and KBr are salts.

Step-by-step solution

Understanding Salt Formation

A salt is commonly formed from the neutralization reaction of an acid and a base. In general, salts are ionic compounds composed of cations (positively charged ions) and anions (negatively charged ions). When dissolved in water, salts dissociate into their respective ions.

Identifying Salts from the List

To determine which of the compounds are salts, we must check if they fit the ionic nature typical of salts, consisting of cations and anions that result from acid-base reactions.

Analyze Each Compound

- **CH₄**: Methane is a covalent compound and not an ionic compound, so it is not a salt. - **NaF**: Sodium fluoride consists of the cation Na⁺ and anion F⁻, resulting from the neutralization of HF with NaOH, making it a salt. - **NaOH**: Sodium hydroxide is a strong base, not a salt. - **CaO**: Calcium oxide is a basic oxide, not a salt. - **BaSO₄**: Barium sulfate consists of the cation Ba²⁺ and anion SO₄²⁻, which are typically formed by neutralization, qualifying it as a salt. - **HNO₃**: Nitric acid is an acid, not a salt. - **NH₃**: Ammonia is a weak base, not a salt. - **KBr**: Potassium bromide consists of the cation K⁺ and anion Br⁻, formed by neutralization of HBr with KOH, making it a salt.

Key concepts

Ionic Compounds

Ionic compounds are a special type of chemical compound made up of ions. These ions are atoms or molecules that have gained or lost electrons, giving them a charge.
The particles in an ionic compound are held together by strong forces of attraction between oppositely charged ions.
The building blocks of ionic compounds are cations and anions:

• Cations are positively charged ions. They are usually formed by metals losing electrons.
• Anions are negatively charged ions, typically formed when nonmetals gain electrons.

Ionic compounds often have high melting and boiling points, and when they dissolve in water, they can conduct electricity due to the free movement of ions.

Acid-Base Neutralization

The process of acid-base neutralization is a chemical reaction where an acid and a base react with each other.
This reaction usually produces a salt and water.
In this context:

• Acids are substances that release hydrogen ions (H⁺) when dissolved in water.
• Bases are substances that provide hydroxide ions (OH⁻) in a solution.

When combined, the hydrogen ions from the acid react with the hydroxide ions from the base to form water, and the remaining ions form a salt. This reaction can be illustrated as:\[\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}\] Through this reaction, the properties of the acid and the base are neutralized, resulting in a neutral pH.

Cation and Anion

Cations and anions are essential components in the formation of ionic compounds.
Here’s a deeper look at how they work:

• Cations: These are positively charged ions. Cations form when an atom loses one or more electrons. For example, the sodium ion (Na⁺) is a cation formed when a sodium atom loses one electron.
• Anions: Anions are negatively charged ions, resulting when an atom gains electrons. For instance, the fluoride ion (F⁻) is an anion created when a fluorine atom gains one electron.

In any ionic compound, the total positive charge from cations equals the total negative charge from anions, ensuring the compound is electrically neutral.

Barium Sulfate

Barium sulfate (\( \text{BaSO}_4 \)) is an example of a salt formed from the reaction between sulfuric acid (\( \text{H}_2\text{SO}_4 \)) and barium hydroxide (\( \text{Ba(OH)}_2 \)).
This compound is primarily recognized for its use in medical imaging, as it is often used as a radiocontrast agent in X-ray imaging.

• The chemical structure consists of the barium cation (\( \text{Ba}^{2+} \)) and the sulfate anion (\( \text{SO}_4^{2-} \)).
• It is insoluble in water, which is why it remains within the digestive system to provide contrast during imaging.

Barium sulfate is highly stable and does not react easily with other substances, making it safe for medical use.

Potassium Bromide

Potassium bromide (\( \text{KBr} \)) is a classic example of an ionic compound formed via acid-base neutralization.
It forms when hydrogen bromide (\( \text{HBr} \)) reacts with potassium hydroxide (\( \text{KOH} \)).

• The potassium ion (\( \text{K}^+ \)) acts as the cation, while the bromide ion (\( \text{Br}^- \)) is the anion of this salt.
• It is highly soluble in water, dissociating into its ions easily, which makes it useful in various applications such as medicine and photography.
• Potassium bromide's simple inorganic structure ensures a clear understanding of ionic bonding.

This salt is fascinating not only for its composition but also for its varied applications in everyday life.