What is the name of Ba(NO2)2 · 3H2O? A) barium(II) nitrite trihydrate B) barium nitrite trihydrate C) trihydrobarium(II) nitrite D) barium nitrate trihydrate E) barium nitrite 34) What is the name of Mn(CO3)2? A) manganese carbide B) magnesium(II) carbonate C) magnesium(IV) carbonate D) manganese(IV) carbonate E) manganese(II) carbonate
The Correct Answer and Explanation is:
Correct Answers:
- Ba(NO₂)₂ · 3H₂O — B) barium nitrite trihydrate
- Mn(CO₃)₂ — D) manganese(IV) carbonate
Explanation:
1. Ba(NO₂)₂ · 3H₂O: Barium nitrite trihydrate
This compound consists of the barium ion (Ba²⁺), two nitrite ions (NO₂⁻), and three water molecules associated as water of hydration. Barium, as an alkaline earth metal in Group 2, typically forms a +2 oxidation state. The nitrite ion carries a -1 charge, so two of them are required to balance the +2 charge of barium.
The anhydrous salt is named barium nitrite. The three attached water molecules are indicated by the prefix “tri-“ and the word “hydrate”, forming trihydrate. Hence, the complete name becomes barium nitrite trihydrate.
Option A incorrectly uses “barium(II)”, which is redundant because barium has only one common oxidation state (+2), making Roman numerals unnecessary. Option C misrepresents the naming order and format. Option D incorrectly uses “nitrate” instead of “nitrite”, changing the identity of the compound. Option E omits the water of hydration.
2. Mn(CO₃)₂: Manganese(IV) carbonate
This compound contains the manganese ion and two carbonate ions (CO₃²⁻). Each carbonate ion carries a -2 charge, so two contribute a total charge of -4. To balance this, manganese must have a +4 oxidation state. Therefore, the manganese cation is Mn⁴⁺.
In naming transition metal compounds, the metal’s oxidation state is shown using Roman numerals in parentheses. The polyatomic anion (carbonate) is named as-is. Combining the name of the cation and the anion gives manganese(IV) carbonate.
Option A refers to a different compound entirely. Option B and C incorrectly list magnesium instead of manganese. Option E assumes Mn is in the +2 oxidation state, which would not balance two carbonate ions.
These names follow the IUPAC rules for naming hydrated ionic and transition metal compounds.
