The volume of a mass of gas is 300 ml at 25 Celsius and 685 torr. What will the gas occupy at STP?

(P1V1/T1) = (P2V2/T2)

To find out what volume the gas will occupy at STP (Standard Temperature and Pressure), we need to use the ideal gas law equation:

PV = nRT

Where:
P = Pressure of the gas
V = Volume of the gas
n = Number of moles of the gas
R = Ideal gas constant
T = Temperature of the gas

At STP, the temperature is 0 degrees Celsius or 273 Kelvin, and the pressure is 1 atmosphere.

First, we need to convert the given temperature from Celsius to Kelvin:
T1 = 25 Celsius + 273 = 298 Kelvin

Next, let's convert the pressure from torr to atmosphere:
P1 = 685 torr / 760 torr = 0.901 atm

Now, we can rearrange the ideal gas law equation to solve for the volume at STP (V2):
V2 = (P1 x V1 x T2) / (P2 x T1)

Plugging in the given values, we have:
V2 = (0.901 atm x 300 ml x 273 K) / (1 atm x 298 K)

Simplifying the equation:
V2 = (0.901 x 300 x 273) / (298)
V2 = 248.36 ml

Therefore, the gas will occupy approximately 248.36 ml at STP.