A compound contains 57.5% Na and 42.5% S by mass. What is the empirical formula of this compound?

• A. NaS
• B. NaS2
• C. Na2S2
• D. Na2S

Answer: (D)

Verified step by step guidance

1. Step 1: Assume you have 100 grams of the compound. This means you have 57.5 grams of Na and 42.5 grams of S.
2. Step 2: Convert the masses of each element to moles by dividing by their atomic masses: use 22.99 g/mol for Na and 32.06 g/mol for S. Calculate moles of Na as \(\frac{57.5}{22.99}\) and moles of S as \(\frac{42.5}{32.06}\).
3. Step 3: Determine the mole ratio by dividing both mole values by the smaller number of moles obtained in Step 2. This will give you the simplest whole number ratio of Na to S atoms.
4. Step 4: If the mole ratio is not a whole number, multiply both ratios by the smallest factor that converts them into whole numbers (e.g., 2, 3, or 4).
5. Step 5: Write the empirical formula using the whole number mole ratios as subscripts for Na and S. For example, if the ratio is approximately 2:1, the empirical formula is \(\mathrm{Na_2S}\).