Question

Combustion analysis of naphthelene, a hydrocarbon used in mothballs, produces 13.20g CO2 and 1.80g H2O. Calculate the empirical formula of nafthelene.

Answer 1

To determine the empirical formula of naphthalene, we need to calculate the moles of carbon and hydrogen in the compound. From the given data, 13.20 g of CO₂ is produced, which is equal to 0.303 mol of CO₂. Similarly, 1.80 g of H₂O is produced, which is equal to 0.100 mol of H₂O. Using these mole ratios, we can determine that the empirical formula of naphthalene is C₃H.

Step-by-step explanation:

To determine the empirical formula of naphthalene, we need to calculate the moles of carbon and hydrogen in the compound. The combustion analysis provides the mass of CO₂ and H₂O produced, which can be used to calculate the moles of carbon and hydrogen. From the given data, 13.20 g of CO₂ is produced, which is equal to 0.303 mol of CO₂. Similarly, 1.80 g of H₂O is produced, which is equal to 0.100 mol of H₂O.

Now, we need to find the mole ratios of carbon to hydrogen. The mole ratio can be found by dividing the number of moles of one element by the number of moles of the other element. In this case, dividing the moles of carbon by the moles of hydrogen gives a ratio of 3.03:1. This ratio can be simplified to 3:1, which means that the empirical formula of naphthalene is C₃H.

Answer 2

Answer: C₃H₂

Step-by-step explanation:

1) Since you are told naphthelene is a hydrocarbon, you know that its chemical formula only has atoms of C and H.

2) Since combustion adds O but not C nor H, you know that all the C and H present in the products come from the naphthelene sample.

3) Calculate the amount of C in 13.20 grams of CO₂:

Use atomic masses:

C: 12.01 g/mol
O: 16.00 g/mol

⇒ molar mass of CO₂ = 12.01 g/mol + 2×16.01 g/mol = 44.01 g/mol

Proportion of C in 13.20 g of CO₂

12.01 g C / 44.01 g CO₂ = x / 13.20 g CO₂ ⇒

x = 13.20 g CO₂ × 12.01 g C / 44.01 g CO₂ = 3.602 g C

3) Calculate the mass of H in 1.80 g of H₂O

Atomic masses:

H: 1.01 g/mol
O: 16.0 g/mol

Molar mass H₂O = 18.02 g/mol

Proportion of H in 1.80 g H₂O

2.02 g H / 18.02 g H₂O = x / 1.80 g H₂O

x = 1.80 gH₂O × 2.02 g H / 18.02 gH₂O = 0.202 g H.

4) Calculate the number of moles of C and H in the masses calculated above

Number of moles of C = 3.602 g C / 12.01 g/mol = 0.3 mol

Number of moles of H = 0.202 g / 1.01 g/mol = 0.2 mol

5) Divide both amounts by the smallest one to calculate the proportion in moles:

C: 0.3 / 0.2 = 1.5 mol

H = 0.2 / 0.2 = 1 mol


Multiply by 2 to obtain integers:

C: 3
H: 2

6) Then the proportion leads to the empirical formula C₃H₂