Question

Name each of the following acids, and assign oxidation numbers to the atoms in each: a. \({HNO}_{2} \) c. \({H}_{2} {CO}_{3}\) b. \({H}_{2} {SO}_{3} \) d. HI

Short answer

a. Nitrous acid, H = +1, N = +3, O = -2. b. Sulfurous acid, H = +1, S = +4, O = -2. c. Carbonic acid, H = +1, C = +4, O = -2. d. Hydroiodic acid, H = +1, I = -1.

Step-by-step solution

- Name the acid \({HNO}_{2}\)

This compound is named 'nitrous acid.' The 'ous' suffix is used because the polyatomic ion is nitrite (\({NO}_{2}^{-}\)).

- Assign oxidation numbers in \({HNO}_{2}\)

Hydrogen (H) typically has an oxidation number of +1. Oxygen (O) typically has an oxidation number of -2. Let the oxidation number of nitrogen (N) be \({x}\). The sum of oxidation numbers in a neutral compound is 0. So, the equation is: \(+1 + x + 2(-2) = 0\). Solving for \({x}\), \({x} = +3\). Therefore, oxidation numbers are: H = +1, N = +3, O = -2.

- Name the acid \({H}_{2} {SO}_{3}\)

This compound is named 'sulfurous acid.' The 'ous' suffix is used because the polyatomic ion is sulfite (\({SO}_{3}^{2-}\)).

- Assign oxidation numbers in \({H}_{2} {SO}_{3}\)

Hydrogen (H) typically has an oxidation number of +1. Oxygen (O) typically has an oxidation number of -2. Let the oxidation number of sulfur (S) be \({x}\). The sum of oxidation numbers in a neutral compound is 0. So, the equation is: \(2(+1) + x + 3(-2) = 0\). Solving for \({x}\), \({x} = +4\). Therefore, oxidation numbers are: H = +1, S = +4, O = -2.

- Name the acid \({H}_{2} {CO}_{3}\)

This compound is named 'carbonic acid.' The 'ic' suffix is used because the polyatomic ion is carbonate (\({CO}_{3}^{2-}\)).

- Assign oxidation numbers in \({H}_{2} {CO}_{3}\)

Hydrogen (H) typically has an oxidation number of +1. Oxygen (O) typically has an oxidation number of -2. Let the oxidation number of carbon (C) be \({x}\). The sum of oxidation numbers in a neutral compound is 0. So, the equation is: \(2(+1) + x + 3(-2) = 0\). Solving for \({x}\), \({x} = +4\). Therefore, oxidation numbers are: H = +1, C = +4, O = -2.

- Name the acid HI

This compound is named 'hydroiodic acid.' The 'hydro' prefix and 'ic' suffix are used because it is a binary acid.

- Assign oxidation numbers in HI

Hydrogen (H) typically has an oxidation number of +1. Iodine (I) would then have an oxidation number of -1 to balance the compound. Therefore, oxidation numbers are: H = +1, I = -1.

Key concepts

naming acids

When naming acids, it's essential to identify whether the acid contains oxygen or not. Acids that do not contain oxygen are called binary acids. For binary acids, the name begins with the prefix 'hydro-', followed by the name of the element, and ends with the suffix 'ic'. For example, HI is named 'hydroiodic acid'.
On the other hand, acids that contain oxygen are named based on the polyatomic ion they contain. If the polyatomic ion ends in '-ate', the acid name will end in '-ic'. If the polyatomic ion ends in '-ite', the acid name will end in '-ous'. For instance, \( {HNO}_{2} \) contains the polyatomic ion nitrite (\( {NO}_{2}^{-} \)), so it is called 'nitrous acid'. Similarly, \( {H}_{2} {CO}_{3} \) contains the carbonate ion (\( {CO}_{3}^{2-} \)), and is called 'carbonic acid'.

oxidation state

Oxidation states, or oxidation numbers, help us track how many electrons are lost or gained by an atom in a compound. The sum of oxidation numbers in a neutral molecule must equal zero.
Some rules to remember include:

• Hydrogen typically has an oxidation state of +1, except when bonded to metals in binary compounds, where it can be -1.
• Oxygen typically has an oxidation state of -2, except in peroxides, where it can be -1.
• Group 1 elements (like sodium) always have an oxidation state of +1, and Group 2 elements (like calcium) always have an oxidation state of +2.

Using these rules, we can determine the unknown oxidation states by setting up an equation where the sum of all oxidation states equals zero. For example, in \( {H}_{2} {SO}_{3} \), we have 2 hydrogens (+1 each), 3 oxygens (-2 each), and an unknown sulfur (\( x \)). The equation is: \ 2(+1) + x + 3(-2) = 0 \, solving for x gives us sulfur's oxidation state as +4.

polyatomic ions

Polyatomic ions are ions that consist of two or more atoms bonded together, carrying a net charge. They play a crucial role in naming acids, especially those containing oxygen.
Some common polyatomic ions include:

• \( {SO}_{4}^{2-} \) (sulfate)
• \( {NO}_{3}^{-} \) (nitrate)
• \( {CO}_{3}^{2-} \) (carbonate)
• \( {PO}_{4}^{3-} \) (phosphate)

When these ions form acids, their suffixes change to '-ic' or '-ous'. For example, sulfate becomes sulfuric acid (\( {H}_{2} {SO}_{4} \)), while sulfite (\( {SO}_{3}^{2-} \)) becomes sulfurous acid (\( {H}_{2} {SO}_{3} \)). Recognizing and memorizing these polyatomic ions will help you efficiently name and work with different acids.

binary acids

Binary acids consist of two elements: hydrogen and one other non-metal element. They do not contain oxygen.
Binary acids are named using the following rules: the name starts with the prefix 'hydro-', followed by the base name of the non-metal element, then ends with the suffix '-ic acid'. For example:

• HCl: hydrochloric acid
• HF: hydrofluoric acid
• HI: hydroiodic acid

These acids typically release H⁺ ions when dissolved in water, which accounts for their acidic properties. Remembering this pattern will help you quickly identify and name binary acids in various chemical contexts.