Problem 65 - General Chemistry: Principles and Modern Applications

Question

Name the acids: (a) \(\mathrm{HClO}_{2} ;\) (b) \(\mathrm{H}_{2} \mathrm{SO}_{3} ;\) (c) \(\mathrm{H}_{2} \mathrm{Se}\) (d) HNO \(_{2}\).

Step-by-Step Solution

Answer

The names of the acids are: (a) chlorous acid; (b) sulfurous acid; (c) hydroselenic acid; (d) nitrous acid.

Step 1: Identifying Type of Acid and Naming HClO2

The molecule HClO2 is an oxyacid, so it's named by using prefix 'hydro-', the root of the anion, and the suffix '-ic', followed by the word 'acid'. The anion ClO2 is called 'chlorite', so when it's an acid, the name will become 'chlorous acid'.

Step 2: Naming H2SO3

The molecule H2SO3 is another oxyacid. The anion here is SO3, which is known as 'sulfite'. So, when it forms an acid, it would be 'sulfurous acid'.

Step 3: Naming H2Se

The molecule H2Se is a binary acid. For binary acids in aqueous solution, we use the prefix 'hydro-', the root of the element, and the suffix '-ic', along with the word 'acid'. Therefore, H2Se becomes 'hydroselenic acid'.

Step 4: Naming HNO2

HNO2 is also an oxyacid. The anion NO2 is known as 'nitrite'. So, when it forms an acid, it would be 'nitrous acid'.

Key Concepts

Oxyacids

Oxyacids are a type of acid that contains hydrogen, oxygen, and another element, which is usually a non-metal. The most important rule for naming oxyacids is to focus on the anion part, which includes oxygen. Oxyacids are related to their corresponding oxyanions—anions that contain oxygen.

• If the anion ends in '-ate', the acid name will change the ending to '-ic'.
• If the anion ends in '-ite', the acid name will change the ending to '-ous'.

Let's look at two examples from the exercise:

• HClO₂ has an anion ClO₂, named chlorite. Thus, it becomes 'chlorous acid' when it forms an acid.
• H₂SO₃ has an anion SO₃, called sulfite. Therefore, it becomes 'sulfurous acid'.

Binary Acids

Binary acids are composed of hydrogen and one other element, usually a halogen or chalcogen. They are relatively simple to name.

• Use the prefix 'hydro-'.
• Take the name of the non-hydrogen element and add the suffix '-ic'.
• Conclude with the word 'acid'.

For example, in the exercise, H₂Se is named using these rules. Since it's a combination of hydrogen and selenium, the name becomes 'hydroselenic acid'. It's important to note that these naming conventions apply when the substance is in an aqueous solution.

Anion Naming

Anions are negatively charged ions formed when an atom or group of atoms gains electrons. The naming of anions is crucial because it often determines the resulting acid's name.

• Anions ending in '-ide' become 'hydro- ___ -ic acid' for binary acids.
• Anions ending in '-ate' switch to '-ic acid'.
• Anions ending in '-ite' switch to '-ous acid'.

Understanding this conversion is key in naming oxyacids and binary acids—a process that directly leads to determining the correct name of the acid.

Chemical Nomenclature

Chemical nomenclature involves a structured system agreed upon by scientists to name chemical compounds. Its significant aspects include naming acids, bases, salts, and more. Acids follow specific patterns based on their composition:

• Binary acids include a simple two-element compound; e.g., H₂Se is named 'hydroselenic acid'.
• Oxyacids include compounds with oxygen; e.g., HNO₂ is named 'nitrous acid'.

These rules help chemists understand compound compositions and properties just by considering their names. Naming conventions like these are proposed by the International Union of Pure and Applied Chemistry (IUPAC), ensuring that chemical names are consistent and universally understandable.