Question

Iron forms a series of compounds of the type Fex(CO)y. In air, they are oxidized to Fe2O3and CO2gas. After heating a 0.142 g sample of Fex(CO)yin air, you isolate the CO2in a 1.50 L flask at 25 °C. The pressure of the gas is 44.9 mmHg. What is the empirical formula of Fex(CO)y

Answer 1

Answer:

The empirical formula is = $Fe(CO)_2$

Explanation:

Carbon dioxide obtained:

Pressure = 44.9 mm Hg

Also, P (mm Hg) = P (atm) / 760

Pressure = 44.9 / 760 = 0.0591 atm

Temperature = 25 °C

The conversion of T( °C) to T(K) is shown below:

T(K) = T( °C) + 273.15  

So,  

T₁ = (25 + 273.15) K = 298.15 K  

V = 1.50 L

Using ideal gas equation as:

PV=nRT

where,  

P is the pressure

V is the volume

n is the number of moles

T is the temperature  

R is Gas constant having value = 0.0821 L.atm/K.mol

Applying the equation as:

0.0591 atm × 1.50 L = n × 0.0821 L.atm/K.mol × 298.15 K  

⇒n = 0.0036 moles

1 mole of carbon atoms are present in 1 mole of carbon dioxide. So,

Moles of C = 0.0036 moles

Molar mass of C atom = 12.0107 g/mol

Mass of C in molecule = 0.0036 x 12.0107 = 0.0432 g

Given that the compound only contains iron and carbon. So,

Mass of Fe in the sample = Total mass - Mass of C

Mass of the sample = 0.142 g

Mass of Fe in sample = 0.142 g - 0.0432 g = 0.0988 g  

Molar mass of Fe = 55.845 g/mol

Moles of Fe  = 0.0988  / 55.845  = 0.0018 moles

Taking the simplest ratio for Fe and C as:

0.0018 : 0.0036

 = 1 : 2

The empirical formula is = $Fe(CO)_2$