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A sample of an unknown substance contains 38.43 g lead, 17.83 g carbon, and 3.74 g hydrogen. What is the empirical formula?

A: PbC4H10
B: Pb2C8H15
C: PbC8H20
D:Pb2C4H15

Answer :

Answer:- C: [tex]PbC_8H_2_0[/tex] .

Solution:- An empirical formula is the simplest whole number ratio of moles of atoms.

Let's convert given grams to moles and calculate the mole ratio as:

moles of Pb = [tex]38.43g(\frac{1mol}{207.2g})[/tex]

moles of Pb = 0.1855

moles of C = [tex]17.83g(\frac{1mol}{12.01g})[/tex]

moles of C = 1.485

moles of H = [tex]3.74g(\frac{1mol}{1.01g})[/tex]

moles of H = 3.703

Let's calculate the mole ratio and for this we divide the moles of each by the least one of them. Least one is Pb as it's moles are least one.

Pb = [tex]\frac{0.1855}{0.1855}[/tex] = 1

C = [tex]\frac{1.485}{0.1855}[/tex] = 8

H = [tex]\frac{3.703}{0.1855}[/tex] = 20

So, the empirical formula of the compound is [tex]PbC_8H_2_0[/tex] and the correct option is C.

samueladesida43

The empirical formula of the unknown substance that contains 38.43 g lead, 17.83 g carbon, and 3.74 g hydrogen is PbC8H20.

HOW TO CALCULATE EMPIRICAL FORMULA:

  • The empirical formula of a substance can be calculated as follows:

  • First, we calculate the number of moles of each element:

  1. Pb = 38.43g ÷ 207g/mol = 0.186 mol
  2. C = 17.83g ÷ 12g/mol = 1.49 mol
  3. H = 3.74g ÷ 1g/mol = 3.74 mol

  • Next, we divide each mole value by the smallest (0.186mol)

  1. Pb = 0.186 mol ÷ 0.186 = 1
  2. C = 1.49 mol ÷ 0.186 = 8.01
  3. H = 3.74 mol = 0.186 = 20.1

  • The empirical ratio of Pb, C and H is 1:8:20. Therefore, the empirical formula is as follows: PbC8H20.

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