High School

Pyrite is a mineral composed of 46.5 mass % iron and 53.5 mass % sulfur. Determine the empirical formula for pyrite.

Answer :

The simplest ratio of iron to sulfur is [tex]1:2[/tex]. The empirical equation is [tex]FeS_2[/tex].

We must convert the mass percentages to moles in order to determine the empirical formula. Given that pyrite is composed of [tex]46.5\%[/tex] iron and [tex]53.5\%[/tex] sulfur, we follow these steps:

Convert mass percentages to grams (assume [tex]100[/tex] grams of pyrite):

  1. Iron: [tex]46.5 grams[/tex]
  2. Sulfur: [tex]53.5 grams[/tex]

Convert grams to moles using atomic masses (Iron: [tex]55.85 g/mol[/tex], Sulfur: 3[tex]2.07 g/mol[/tex]):

  1. Moles of Iron: [tex]\frac{46.5 \, \text{g}}{55.85 \, \text{g/mol}} \approx 0.833 \, \text{moles}[/tex]
  2. Moles of Sulfur: [tex]\frac{53.5 \, \text{g}}{32.07 \, \text{g/mol}} \approx 1.669 \, \text{moles}[/tex]

Divide the moles by the smallest number of moles to find the simplest ratio:

  1. Moles of Iron: [tex]\frac{0.833}{0.833} \approx 1[/tex]
  2. Moles of Sulfur:[tex]\frac{1.669}{0.833} \approx 2[/tex]

Hence, the empirical formula is [tex]FeS_2[/tex].

The empirical formula for pyrite is FeS2.

HOW TO CALCULATE EMPIRICAL FORMULA:

  • The empirical formula represents the simplest whole number ratio of constituents element of a compound. The empirical formula of pyrite can be calculated as follows:

46.5 mass % Fe = 46.5g of Fe

53.5 mass % S = 53.5g of S

  • Next, we divide each element's mass value by its molar mass

Fe = 46.5g ÷ 56g/mol = 0.83mol

S = 53.5g ÷ 32g/mol = 1.67mol

  • Next, we divide each mole value by the smallest (0.83mol)

Fe = 0.83mol ÷ 0.83 = 1

S = 1.67mol ÷ 0.83 = 2.014

Approximately, the ratio of Fe to S is 1:2. Therefore, the empirical formula of pyrite is FeS2.

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