Summary of Inorganic Functions: Acids

Inorganic Functions: Acids | Traditional Summary

Contextualization

Acids are fundamental chemical substances that play a crucial role in both biological and industrial processes, being essential for life and various human activities. In everyday life, we find acids in foods, such as citric acid present in lemons and vinegar, and in cleaning products, like hydrochloric acid. Understanding acids, their properties, and classifications is an important step to understanding chemistry more broadly.

In addition to being present in our daily lives, acids have a vast range of industrial applications. Sulfuric acid, for example, is widely used in the production of fertilizers, petroleum refining, and the manufacture of chemical products. Acetic acid is an essential component in the food industry, used in the production of preservatives and seasonings. Understanding the characteristics and uses of acids not only allows for a better perception of the world around us but also practical application of this knowledge in various fields.

Definition of Acids

Acids are chemical substances that, when dissolved in water, release hydrogen ions (H⁺). This definition is based on Arrhenius' theory, which specifies that an acid is a substance that increases the concentration of H⁺ ions in aqueous solutions. The presence of these ions is responsible for the characteristic properties of acids, such as sour taste and the ability to react with bases to form salts and water.

In addition to the Arrhenius definition, other theories also explain acid behavior. The Brønsted-Lowry theory, for example, defines acids as proton donors (H⁺), while the Lewis theory describes acids as electron pair acceptors. These definitions expand the understanding of what constitutes an acid and help explain a wider range of chemical reactions.

The release of hydrogen ions is a fundamental process that occurs in several important chemical reactions. For example, when hydrochloric acid (HCl) is dissolved in water, it completely dissociates, releasing H⁺ and Cl⁻ ions. This complete dissociation is characteristic of strong acids, which ionize totally in solution.

• Acids release hydrogen ions (H⁺) in aqueous solution.

• Arrhenius definition: increase in H⁺ concentration in aqueous solutions.

• Other theories: Brønsted-Lowry (proton donors) and Lewis (electron pair acceptors).

Properties of Acids

Acids exhibit several characteristic properties that distinguish them from other chemical substances. One of the most notable properties is the sour taste, which can be easily identified in foods such as lemons and vinegar. However, it is important to remember that many acids are corrosive and should not be tasted directly.

Another important property of acids is their ability to change the color of indicators. For example, blue litmus paper turns red in the presence of an acid. Other common indicators include phenolphthalein, which turns colorless in acidic solutions, and methyl orange, which changes from orange to red.

Furthermore, acids react with metals, releasing hydrogen gas (H₂). This reaction is often used in laboratory experiments to demonstrate the reactivity of acids. Acids also neutralize bases, forming salt and water, a process known as neutralization.

• Characteristic sour taste.

• Color change of indicators (e.g., blue litmus turning red).

• Reactivity with metals releasing hydrogen.

• Neutralization of bases forming salt and water.

Classification of Acids

Acids can be classified in various ways, depending on their properties and composition. One of the most common classifications is based on the strength of the acid: strong acids and weak acids. Strong acids, such as hydrochloric acid (HCl) and sulfuric acid (H₂SO₄), completely ionize in aqueous solution. In contrast, weak acids, such as acetic acid (CH₃COOH), ionize only partially.

Another form of classification is based on the number of ionizable hydrogens. Monoprotic acids are those that release a single H⁺ ion, such as HCl. Diprotic acids release two H⁺ ions, such as H₂SO₄, and triprotic acids release three H⁺ ions, such as H₃PO₄. This classification is important for understanding an acid's ability to generate protons in solution.

Acids can also be divided into binary acids and oxyacids, based on the presence of oxygen. Binary acids, like HCl, do not contain oxygen, while oxyacids, like HNO₃ (nitric acid), contain oxygen in their structure. This distinction helps understand the different properties and reactivities of acids.

• Classification by strength: strong and weak acids.

• Classification by the number of ionizable hydrogens: monoprotic, diprotic, triprotic.

• Classification by the presence of oxygen: binary acids and oxyacids.

Nomenclature of Acids

The nomenclature of acids follows specific rules depending on their composition. For binary acids that do not contain oxygen, the nomenclature is straightforward: the prefix 'acid' is used followed by the name of the element with the suffix '-ic'. For example, HCl is called hydrochloric acid, and HBr is called hydrobromic acid.

For oxyacids that contain oxygen, the nomenclature is a bit more complex. These acids are named based on the anion derived from the acid. If the anion ends in '-ate', the corresponding acid ends in '-ic'. For example, HNO₃, which contains the anion nitrate (NO₃⁻), is called nitric acid. If the anion ends in '-ite', the corresponding acid ends in '-ous'. For example, HNO₂, which contains the anion nitrite (NO₂⁻), is called nitrous acid.

This nomenclature is important because it helps identify the composition and structure of the acid, facilitating the understanding of its properties and reactions. Moreover, the correct nomenclature is crucial for precise communication in chemistry, both in academic and industrial contexts.

• Binary acids: prefix 'acid' + name of the element + '-ic'.

• Oxyacids: anion '-ate' -> acid '-ic'; anion '-ite' -> acid '-ous'.

• Nomenclature facilitates the identification of the composition and properties of acids.

Applications of Acids

Acids have a wide range of applications both in daily life and in various industries. In everyday life, we find acids in foods and cleaning products. Citric acid, for example, is common in citrus fruits like lemons and oranges, giving them a sour taste. Acetic acid is the main component of vinegar, widely used in cooking and food preservation.

In industry, acids play crucial roles in many processes. Sulfuric acid (H₂SO₄) is one of the most produced chemicals in the world and is used in the manufacture of fertilizers, in petroleum refining, and in the production of chemical products. Hydrochloric acid (HCl) is widely used in metal cleaning and the production of polyvinyl chloride (PVC).

Moreover, acids have significant applications in biology and medicine. Ascorbic acid (vitamin C) is essential for human health, acting as an antioxidant and aiding in collagen synthesis. Acetylsalicylic acid (aspirin) is a common medication used to relieve pain and reduce inflammation. These applications demonstrate the importance of acids in various aspects of life and industry.

• Acids in foods: citric acid (citrus fruits), acetic acid (vinegar).

• Acids in industry: sulfuric acid (fertilizers, petroleum refining), hydrochloric acid (metal cleaning, PVC production).

• Acids in biology and medicine: ascorbic acid (vitamin C), acetylsalicylic acid (aspirin).

To Remember

• Acids: Substances that release hydrogen ions (H⁺) in aqueous solution.

• Arrhenius definition: Specifies that an acid is a substance that increases the concentration of H⁺ ions in aqueous solutions.

• Brønsted-Lowry definition: Defines acids as proton donors (H⁺).

• Lewis definition: Defines acids as electron pair acceptors.

• Indicators: Substances that change color in the presence of acids or bases.

• Strong Acid: An acid that completely ionizes in aqueous solution.

• Weak Acid: An acid that partially ionizes in aqueous solution.

• Monoprotic: Acid that releases a single H⁺ ion.

• Diprotic: Acid that releases two H⁺ ions.

• Triprotic: Acid that releases three H⁺ ions.

• Binary Acid: Acid that does not contain oxygen.

• Oxyacid: Acid that contains oxygen.

• Nomenclature of Binary Acids: Prefix 'acid' + name of the element + '-ic'.

• Nomenclature of Oxyacids: Anion '-ate' -> acid '-ic'; anion '-ite' -> acid '-ous'.

• Sulfuric Acid: Used in the manufacture of fertilizers and in petroleum refining.

• Hydrochloric Acid: Used in metal cleaning and in the production of PVC.

• Citric Acid: Common component in citrus fruits.

• Acetic Acid: Main component of vinegar.

• Ascorbic Acid: Known as vitamin C, essential for human health.

• Acetylsalicylic Acid: Commonly known as aspirin, used to relieve pain and reduce inflammation.

Conclusion

In this lesson, we discussed the definition and properties of acids, highlighting their ability to release hydrogen ions (H⁺) in aqueous solution, which gives them characteristics such as sour taste and reactivity with metals. We also addressed the different forms of acid classification, such as strength (strong and weak), the number of ionizable hydrogens (monoprotic, diprotic, triprotic), and the presence of oxygen (binary acids and oxyacids). Furthermore, we learned the rules of acid nomenclature and explored their various applications in daily life and industry, from food and cleaning products to medicines and industrial processes.

Understanding acids is fundamental to chemistry and many daily practices. Knowledge about their properties and classifications allows for a better comprehension of their reactions and uses. This topic is especially relevant for chemistry students, as it provides a solid foundation for the study of other inorganic functions and chemical reactions.

We encourage students to continue exploring the topic on their own, conducting simple experiments with acids found at home, like vinegar and lemon juice, and studying more about their industrial and biological applications. This knowledge not only enriches chemical understanding but also broadens the perception of the world around us.

Study Tips

• Reread and note the main concepts discussed in class, such as the definition, properties, and classifications of acids.

• Conduct simple experiments at home using common acidic substances to observe their properties and reactions.

• Explore books and online resources about inorganic chemistry to deepen your knowledge about acids and their applications.