How many moles of gas are contained in 890.0 mL at 21.0 °C and 0.99 atm pressure?

To determine the number of moles of gas in a given volume, temperature, and pressure, we can use the ideal gas law equation:

PV = nRT

Where:
P = pressure (0.99 atm)
V = volume (890.0 mL or 0.890 L)
n = number of moles
R = ideal gas constant (0.0821 L atm / mol K)
T = temperature (21.0°C or 294.15 K)

First, convert the volume from mL to liters:
0.890 L

Next, plug in the values into the ideal gas law equation:

(0.99 atm)(0.890 L) = n(0.0821 L atm / mol K)(294.15 K)

0.8781 = 24.20145n

n = 0.0363 moles

Therefore, there are 0.0363 moles of gas contained in 890.0 mL at 21.0 °C and 0.99 atm pressure.