Question

Acetylene, a fuel used in welding torches, is composed of 92.3% C and 7.7% H by mass. Find the empirical formula. If 1.10 g of acetylene occupies of volume of 1.00 L at 1.15 atm and 59.5°C, what is the molecular formula for acetylene?

Answer 1

C2H2

Step-by-step explanation:

To find the empirical formula, we assume 100 g of the compound. Therefore, the mass of carbon is 92.3 g and the mass of hydrogen is 7.7 g.

We can convert these masses into moles by dividing by their respective atomic masses:

92.3 g C / 12.01 g/mol = 7.690 mol C

7.7 g H / 1.008 g/mol = 7.634 mol H

We can divide each of these by the smaller of the two numbers (7.634 mol) to get the simplest, whole-number ratio:

7.690 mol C / 7.634 mol H = 1.005

This is approximately a 1:1 ratio, so the empirical formula is CH.

To find the molecular formula, we need to know the molar mass of the compound. We can find this by using the ideal gas law:

PV = nRT

n = PV/RT

n = (1.15 atm * 1.00 L) / (0.08206 L atm/mol K * 332.65 K)

n = 0.0459 mol

Now we can calculate the molar mass:

molar mass = 1.10 g / 0.0459 mol = 24.0 g/mol

We can compare this to the empirical formula mass (12.01 g/mol for C and 1.008 g/mol for H) to find the molecular formula:

molecular formula = (empirical formula)n

24.0 g/mol = (12.01 g/mol + 1.008 g/mol)n

n = 1.81

Therefore, the molecular formula is C2H2.