Multiple Choice
Which of the following is the correct chemical formula for copper(II) bromide?
3. Chemical Reactions
Naming Ionic Compounds
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Which of the following is the correct chemical formula for cobalt(II) sulfide?
A
Co2S3
B
CoS
C
CoS2
D
CoSO4
Verified step by step guidance1
Identify the charge of the cobalt ion in cobalt(II) sulfide. The Roman numeral II indicates that cobalt has a +2 charge, so the ion is Co^{2+}.
Determine the charge of the sulfide ion. Sulfide is the anion formed from sulfur with a charge of 2-, so the ion is S^{2-}.
Combine the cobalt(II) ion and the sulfide ion in a ratio that balances the total positive and negative charges to zero. Since Co^{2+} and S^{2-} have charges of equal magnitude but opposite sign, they combine in a 1:1 ratio.
Write the chemical formula by placing the symbols of cobalt and sulfur with their respective subscripts indicating the number of each ion. Because the charges balance 1:1, the formula is CoS.
Verify that the formula is electrically neutral by confirming that the total positive charge from cobalt equals the total negative charge from sulfide.
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