What is the formula of chromium(III) carbonate?
A) Cr₂(CO₃)₃
B) Cr(CO₃)₃
C) Cr₃CO₃
D) Cr₃(CO₃)₂
The Correct Answer and Explanation is :
The correct formula for chromium(III) carbonate is B) Cr(CO₃)₃.
Explanation:
To derive the formula for chromium(III) carbonate, we need to understand the oxidation states of chromium and the carbonate ion.
- Oxidation State of Chromium: In chromium(III) carbonate, chromium has an oxidation state of +3. This is indicated by the Roman numeral III in the name, which specifies that chromium is in the +3 oxidation state.
- Carbonate Ion: The carbonate ion (CO₃) has a charge of -2. This means that each carbonate ion can balance the positive charge of the metal cation (chromium, in this case).
- Balancing Charges: To balance the +3 charge of one chromium ion, we need multiple carbonate ions. Specifically, we need two carbonate ions to offset the charge because:
- 1 Cr³⁺ contributes +3
- 2 CO₃²⁻ ions contribute -4 (since each CO₃ has a charge of -2, two CO₃ ions will total -4)
However, having two CO₃ ions would make the overall formula Cr(CO₃)₂, leading to a net charge of +1 on chromium. Therefore, we can only use one Cr³⁺ ion with three carbonate ions to maintain charge neutrality:
- 1 Cr³⁺ contributes +3
- 3 CO₃²⁻ ions contribute -6
To achieve overall neutrality, you would actually need to take into account that for every three carbonate ions, you would still only have one chromium ion since each ion requires balancing with +2 charge. Thus, the complete formula would be Cr(CO₃)₃.
In summary, the correct formula reflects the +3 oxidation state of chromium combined with three carbonate ions, resulting in the correct formula: Cr(CO₃)₃.