Question

For the reaction

2 HCl + Na₂CO₃ ----> 2 NaCl + H₂O + CO₂

8.0 moles of CO₂ is collected at STP. What is the volume of CO₂?

1.) 2.80 L

2.) 179 L

3.) 57.6 L

4.) 0.0250 L

5.) 22.4 L

6.) 0.357 L

Answer 1

Ans. Ideal gas equation:         PV = nRT        - equation 1

            Where, P = pressure in atm

            V = volume in L                     

            n = number of moles

            R = universal gas constant= 0.0821 atm L mol^-1K^-1

            T = absolute temperature (in K)

IUPAC defines STP as temperature of 0⁰C (= 273.15 K) and pressure of 10⁵ pascals.

            10⁵ Pa = 0.98692 atm                         ; [1 Pa = 9.8692 x 10^-6 atm]

So, we have-

            Pressure = 0.98692 atm

            T = 273.15 K

            Number of moles, n = 8.0 mol

Putting the values in equation 1-

            0.98692 atm x V = 8.0 mol x (0.0821 atm L mol^-1K^-1) x 273.15 K

            Or, V = 181.6884 L

Thus, volume of CO2 at STP = 181.6884 L

Correct option: 2. 179 L

Note: The deviation in volume of around 2.6 L have occurred due to accounting 10⁵ Pa as the standard pressure. If you use 1.0 atm as standard pressure, you get a value of 179.2 L. Be careful, however, standard pressure = 10⁵ Pa (= 0.98692 atm) ; but not 1.0 atm.