A particular sample of pantothenic acid, a B vitamin, gives off 72.6 mL of nitrogen gas at 23 degrees c and 795 torr. What is the volume of the nitrogen at STP?

70.04 mL.

Explanation:

We can use the general law of ideal gas: V = nRT.

where, P is the pressure of the gas in atm.

V is the volume of the gas in L.

n is the no. of moles of the gas in mol.

R is the general gas constant,

T is the temperature of the gas in K.

If n is constant, and have two different values of V, P and T:

P₁V₁T₂ = P₂V₂T₁

P₁ = 795 torr, V₁ = 72.6 mL, T₁ = 23.0 °C + 273 = 296 K.

P₂ = 760 torr (standard pressure = 1 atm = 760 torr), V₂ = ? mL, T₂ = 0.0 °C + 273 = 273 K (standard T).

∴ V₂ = P₁V₁T₂/P₂T₁ = (795 torr) (72.6 mL) (273 K) / (760 torr) (296 K) = 70.04 mL.