Find how many moles of gas

Question

Assuming you collected 65.4mL of gas in the reaction with zinc, how many moles of gas would have been produced at 22°C and 103kPa?

Answer 1

65.4 mL of gas = 0.0654 Liters

22 C = 295 K

103 kPa = 0.98 atmospheres

Using PV = nRT, solve for n using R (gas constant) = 0.082 L-atm/mole -deg

n = 0.98 atm x 0.0654 L / 0.082 L-atm/mole -deg x 295 K = 2.65 x 10^-3 moles

This neglects the vapor pressure of water if the gas was collected over water. In that case, the vapor pressure of water at 295 K would need to be subtracted from the total pressure to get the pressure of the gas before using the gas law equation.

Answer 2

Ideal gas law

PV = nRT

P = pressure in atm = 103 kP x 1 atm / 101.325 kPa = 1.02 atm

V = volume in L = 65.4 ml x 1 L / 1000 ml = 0.0654 L

n = moles = ?

R = gas constant = 0.0821 Latm/Kmol

T = temperature in K = 22ºC + 273 = 295K

Substituting and solving for moles (n), we have...

PV = nRT

n = PV/RT

n = (1.02 atm)(0.0654 L) / (0.0821 Latm/Kmol)(295K)

n = 0.00274 moles of gas