Question

Which of the following has been named correctly? (1) \(\mathrm{S}_{2} \mathrm{O}_{3}{ }^{2-}\) thiosulphite ion (2) \(\mathrm{N}_{3}\) - nitride ion (3) HAsO \(_{3}^{-2}\) monohydrogenarsenite ion (4) \(\mathrm{H}_{2} \mathrm{PO}_{4}\) - dihydrogenphosphite ion

Short answer

Option (4): \( \text{H}_{2} \text{PO}_{4}- \) dihydrogenphosphite ion is correct.

Step-by-step solution

Identify the correct name for \(\frac{\text{S}_{2} \text{O}_{3}{ }^{2-}}}{thiosulphite ion}

The formula \( \text{S}_{2} \text{O}_{3}{ }^{2-}\) represents the thiosulfate ion, not the thiosulphite ion. Thiosulphite ion does not exist.

Identify the correct name for \( \text{N}_{3} \)

The formula \( \text{N}_{3}- \) represents the azide ion, not the nitride ion. The correct name for the nitride ion is \( \text{N}^{3-} \).

Identify the correct name for \(\text{HAsO}_{3}^{2-} \)

The formula \( \text{HAsO}_{3}^{2-} \) is incorrectly referred to as the monohydrogenarsenite ion. The correct name should be the hydrogenarsenite ion.

Identify the correct name for \( \text{H}_{2} \text{PO}_{4} \)

The formula \( \text{H}_{2} \text{PO}_{4}- \) is correctly named dihydrogenphosphite ion.

Select the correctly named formula

From the above steps, determine the formula that is correctly named. The formula correctly named is \( \text{H}_{2} \text{PO}_{4}- \) which is dihydrogenphosphite ion.

Key concepts

Ion Naming Conventions

Understanding ion naming conventions in chemistry is crucial for accurate communication and comprehension of chemical formulas. Let's break down some key points:

• For simple anions (negatively charged ions), you typically add the suffix '-ide' to the root of the element's name. For example, Cl^- is named chloride.


• For oxoanions (anions that contain oxygen), different suffixes and prefixes are used based on the number of oxygen atoms. The suffix '-ate' is used for the most common form, and '-ite' is used for an anion with one fewer oxygen atom. For example, NO3^- is nitrate, while NO2^- is nitrite.


• When an additional proton is added, prefixes like 'hydrogen' or 'dihydrogen' are used. For example, HPO42- is hydrogen phosphate, and H2PO4^- is dihydrogen phosphate.

The thiosulphate ion, represented as S2O32-, is an example of an oxoanion with an oxygen replaced by sulfur. Getting familiar with these rules helps in naming ions correctly, thus avoiding confusion.

Oxidation States

Oxidation states, or oxidation numbers, indicate the number of electrons an atom has lost or gained. They are crucial in redox reactions and for naming compounds properly.

• The oxidation state of a free element is always zero. For instance, the oxidation state of Na in Na metal is 0.


• For monoatomic ions, the oxidation state is equal to the charge of the ion, just like Na+ has an oxidation state of +1.


• Oxygen typically has an oxidation state of -2, while hydrogen is usually +1 when combined with non-metals and -1 with metals.


• In polyatomic ions, the sum of the oxidation states of all atoms equals the charge on the ion. For example, in thiosulphate (S2O32-), the sum of oxidation states of sulfur and oxygen equals -2.

Mastering the determination of oxidation states helps in understanding the chemical behavior of compounds and correctly naming complex ions.

Chemical Nomenclature Mistakes

Chemical nomenclature mistakes can lead to significant misunderstandings. Here are some common pitfalls:

• Confusing similar terms: It's easy to mix up ions with similar names like nitrite (NO2^-) and nitrate (NO3^-). Remember that the number of oxygen atoms affects the suffix.


• Incorrectly naming complex ions: For instance, HAsO32- should be named 'hydrogen arsenite,' not 'monohydrogenarsenite'. Being precise with naming conventions of hydrogenated ions is crucial.


• Mistaking the prefix: Do not overlook the prefixes 'hydro-', 'di-', etc. For example, H2PO4^- is 'dihydrogen phosphite,' not just 'phosphite.' The prefix indicates important details about the hydrogen atoms present in the ion.
• Misinterpreting oxidation states: Incorrectly assigning oxidation states can lead to wrong names. Always cross-check oxidation states to ensure accuracy.

Regular practice and careful attention to chemical nomenclature rules can significantly reduce such errors, ensuring clear and consistent communication in chemistry.