Multiple Choice
Which of the following is the correct chemical formula for aluminum nitrate?
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3. Chemical Reactions
Naming Ionic Compounds
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Which of the following is the correct formula for the ionic compound formed between magnesium and sulfur?
A
MgS
B
Mg_2S_2
C
MgS_2
D
Mg_2S
Verified step by step guidance1
Identify the charges of the ions formed by magnesium and sulfur. Magnesium typically forms a $\mathrm{Mg^{2+}}$ ion, and sulfur typically forms a $\mathrm{S^{2-}}$ ion.
Determine the ratio of ions needed to balance the overall charge of the compound. Since $\mathrm{Mg^{2+}}$ has a +2 charge and $\mathrm{S^{2-}}$ has a -2 charge, one $\mathrm{Mg^{2+}}$ ion will balance one $\mathrm{S^{2-}}$ ion.
Write the formula by combining the ions in the ratio that balances the charges. Because the charges are equal and opposite, the formula is simply $\mathrm{MgS}$ with no additional subscripts needed.
Check the other options to see if they represent the same ratio or if they imply different charge balances. For example, $\mathrm{Mg_2S_2}$ simplifies to $\mathrm{MgS}$, but it is not the conventional way to write the formula.
Conclude that the correct formula for the ionic compound formed between magnesium and sulfur is $\mathrm{MgS}$, reflecting the 1:1 ratio of $\mathrm{Mg^{2+}}$ to $\mathrm{S^{2-}}$ ions.
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