Write the chemical formula for the chromate ion
The correct answer and explanation is:
Correct Answer: CrO₄²⁻
The chromate ion is a polyatomic ion that contains one chromium atom and four oxygen atoms. Its chemical formula is CrO₄²⁻, and it carries a -2 charge. This ion is part of a group known as oxoanions, which are composed of a central atom (in this case, chromium) bonded to oxygen atoms.
Chromate belongs to the family of compounds known as transition metal oxoanions, where a transition metal (chromium) is bonded to oxygen. Chromium in this ion is in the +6 oxidation state. Each oxygen atom typically contributes a -2 oxidation number. When four oxygen atoms are present, their total oxidation number is -8. To balance this and arrive at the overall -2 charge of the ion, the chromium must have an oxidation state of +6. This ensures that the charges balance: +6 (from chromium) and -8 (from oxygen), giving a total of -2.
Chromate is often found in various salts and is known for its bright yellow color. It is commonly encountered in inorganic chemistry and is related to the dichromate ion (Cr₂O₇²⁻), which contains two chromium atoms and seven oxygen atoms. These two ions can convert into each other in solution depending on the pH. In basic conditions, chromate is more stable. In acidic conditions, chromate ions combine to form dichromate.
Chromate ions are strong oxidizing agents and are used in various industrial processes, such as metal plating, pigments, and corrosion inhibition. However, due to the toxicity and carcinogenic nature of hexavalent chromium compounds, handling chromates requires proper safety precautions.
In summary, CrO₄²⁻ is the correct formula for the chromate ion, and it reflects the balance between the positively charged chromium and the negatively charged oxygen atoms, resulting in an ion with an overall -2 charge.