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and at 75F?

75 F – 32 = 1.8 Celsius
43 = 1.8 Celsius
temp = 23.9 Celsius ==== 297 Kelvin

300 cm Hg @ 1 atm / 76 cm Hg = 3.947 atm

find moles of oxygen
PV = nRT
(3.947 atm)(3000 litres) = n (0.0821 L-atm/mol-K)(297Kelvin)
n = 485.66 moles of oxygen

use molar mass to find mass of oxygen:
485.66 moles oxygen @ 32.00 g/mol =
your answer:
15,541 grams of oxygen

but if this is a 3 sigfig problem, we should round off to
15,500 grams of oxygen

2 Responses

1. Steve O Says:
   January 3rd, 2010 at 3:16 am

   75 F – 32 = 1.8 Celsius
   43 = 1.8 Celsius
   temp = 23.9 Celsius ==== 297 Kelvin

   300 cm Hg @ 1 atm / 76 cm Hg = 3.947 atm

   find moles of oxygen
   PV = nRT
   (3.947 atm)(3000 litres) = n (0.0821 L-atm/mol-K)(297Kelvin)
   n = 485.66 moles of oxygen

   use molar mass to find mass of oxygen:
   485.66 moles oxygen @ 32.00 g/mol =
   your answer:
   15,541 grams of oxygen

   but if this is a 3 sigfig problem, we should round off to
   15,500 grams of oxygen
   References :

2. Dr. Lucafont Says:
   January 3rd, 2010 at 3:55 am

   Use the ideal gas law! Isolate the mass in the formula.

   PV = nRT
   PV = (mass / molar mass)RT
   PV / RT = mass / molar mass
   PV(molar) / RT = mass

   I’ll use the gas constant R as 0.0821 Latm/molK. In this case, we’re going to do some conversions in our numerical data. Convert °F to K, and convert cmHg to atm.

   For the temperature:
   °C = 5/9(°F – 32)
   °C = 5/9(75 – 32)
   °C = 23.9°C

   K = °C + 273
   K = 23.9°C + 273
   K = 297 K

   For the pressure:
   1 cmHg = 10 mmHg
   300 cmHg = 3000 cmHg

   1 atm = 760 mmHg
   150/38 atm = 3000 mmHg

   Solve for the mass of oxygen.

   PV(molar) / RT = mass
   (150/38 atm)(3.00 x 10³ L)(32.00 g/mol) / (0.0821)(297 K) = mass
   1.55 x 10⁴ g O2 = mass (Answer)

   Hope this helps!
   References :

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