You have 2.394 x 102 ml of oxygen gas (o2) at 7.20 x 102 mm of hg and 78 oc.
what is the mass of the sample in milligrams?

We are given with
V = 2.394 x 102 mL 
P = 7.20 x 102 mm of Hg
T = 78 oC

We are asked to determine the mass of the sample in milligrams
Using the ideal gas law
n = PV / RT
n = 7.20 x 102 mm of Hg (2.394 x 102 mL) / R (78 + 273)
Use the appropriate value for R or just convert the values to SI and use R = 8.314
Then, solve for the mass of the sample by using the MW Oxygen which is 16 g/mol

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