What is the formula for cobalt(III) sulfide?
a. Co3S
b. CoS3
c. Co2S3
d. Cu2S3
The Correct Answer and Explanation is :
The correct formula for cobalt(III) sulfide is c. Co₂S₃.
Explanation:
Cobalt(III) sulfide is a compound formed from cobalt ions in the +3 oxidation state and sulfide ions. To derive the correct formula, we need to consider the charges of the ions involved.
- Understanding Ion Charges:
- Cobalt (Co) can exist in several oxidation states, including +2 and +3. In cobalt(III) sulfide, cobalt is in the +3 oxidation state (Co³⁺).
- Sulfide (S) has a charge of -2 (S²⁻).
- Balancing the Charges:
- To form a neutral compound, the total positive charge must equal the total negative charge. Since cobalt is +3, we need to determine how many cobalt ions are required to balance the charge of sulfide ions.
- Each sulfide ion has a charge of -2. If we have three sulfide ions (3 × -2 = -6), we will need enough cobalt ions to balance this charge.
- To balance the -6 charge from the three sulfide ions, we need two cobalt ions (2 × +3 = +6).
- Constructing the Formula:
- With two cobalt ions (Co²⁺) and three sulfide ions (S²⁻), we can write the empirical formula for cobalt(III) sulfide as Co₂S₃.
- Why the Other Options Are Incorrect:
- a. Co₃S: This suggests three cobalt ions and one sulfide ion, which would lead to an overall charge of +9, not balanced.
- b. CoS₃: This indicates one cobalt ion and three sulfide ions, leading to an unbalanced +3 to -6 charge.
- d. Cu₂S₃: This is incorrect as it suggests copper (Cu) rather than cobalt (Co).
In summary, cobalt(III) sulfide is correctly represented by the formula Co₂S₃, which accurately reflects the charges and composition of the compound.