Multiple Choice
Which of the following is the correct chemical formula for aluminum sulfide?
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3. Chemical Reactions
Naming Ionic Compounds
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Which of the following is the correct formula unit for a compound formed from Fe^{3+} ions and oxide ions (O^{2-})?
A
Fe_2O_3
B
FeO
C
Fe_3O_2
D
FeO_2
Verified step by step guidance1
Identify the charges of the ions involved: Fe^{3+} has a charge of +3, and O^{2-} has a charge of -2.
Determine the ratio of Fe^{3+} ions to O^{2-} ions needed to balance the total positive and negative charges so that the compound is electrically neutral.
Set up the charge balance equation: (number of Fe ions) \times (+3) + (number of O ions) \times (-2) = 0.
Find the smallest whole number ratio of Fe to O that satisfies the charge balance. This involves finding the least common multiple (LCM) of the charges 3 and 2, which is 6.
Use the ratio to write the empirical formula: since 2 Fe^{3+} ions contribute +6 charge and 3 O^{2-} ions contribute -6 charge, the formula unit is Fe_2O_3.
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