A 630. mL flask contains O2 at a pressure of 0.75 atm and a temperature of 20°C. What mass of O2 is present?
I know you Use PV = nRT and solve for n = number of mols gas. Then n = grams/molar mass and solve for grams.
But I get the wrong answer
Show your work and let us find the error. A common error is not using kelvin for temperature. Also remember volume must be in L
630 ml= 1l= 1000ml
0.63 L
20=293.15 k
0.75*0.63=n*0.0821*293.15
=1687.13002
630 mL = 0.630 L; right.
20 C is 20+273 = 293K; right.
0.75atm x 0.630L = n*0.08206*293
n = 0.0196 mols. I suspect you just punched in the wrong numbers or hit the wrong button somewhere on your calculator. Also you quit when you had n.
Then n = grams/molar mass
0.0196 = g/32
g = 32*0.0196 = approx 0.64 g
To calculate the mass of O2 present in the flask, we can use the ideal gas law equation, PV = nRT, as you correctly mentioned. Let's break down the steps to solve the problem correctly:
Step 1: Convert the given volume of the flask from milliliters (mL) to liters (L):
630 mL ÷ 1000 mL/L = 0.63 L
Step 2: Convert the given pressure from atm to Pascal (Pa):
1 atm = 101325 Pa
0.75 atm × 101325 Pa/atm = 75994 Pa
Step 3: Convert the given temperature from Celsius (°C) to Kelvin (K):
T(K) = T(°C) + 273.15
20°C + 273.15 = 293.15 K
Step 4: Calculate the number of moles (n) of O2 using the ideal gas law equation:
PV = nRT
n = (PV) / (RT)
n = (75994 Pa * 0.63 L) / (8.314 J/(mol K) * 293.15 K)
n ≈ 0.152 mol
Step 5: Calculate the mass of O2:
To determine the mass of O2, we need to use the molar mass of O2, which is approximately 32 g/mol.
Mass = n * molar mass
Mass = 0.152 mol * 32 g/mol
Mass ≈ 4.864 g
Therefore, the mass of O2 present in the flask is approximately 4.864 grams. Make sure to double-check your calculations and units to ensure accuracy.