total pressure?

Question

At 0°C a 1.00 L flask contains 8.40 10-2 mol N2, 5.40 102 mg O2, and NO at a concentration of 9.00 1018 molecules/cm3. What is the partial pressure of each gas, and what is the total pressure in the flask?
PN2 = ____ atm
PO2 = ___ atm
PNO = ___ atm
Ptotal = ____ atm

Answer 1

The trick is to take the problem one bit at a time, so that it does not overwhelm your working memory.

As usual in gas law problems, you need to use the equation

PV = nRT

In this case, you asked to find out P for each gas, and if you add them up that will give you the total pressure. You are told V (1 L), and T (273.15 K), so you need to find out n for each gas. Remember to choose R in L atm K-1 mol-1, so that units match.

For N2, you are told n

For O2, you are told the mass in mg. To get from mass to moles, you convert to g and divide by the molar mass (g/mol).

For NO, you are told the number of molecules per cm^3. Find out the number of molecules in your vessel, and convert to number of moles using Avogadro's number.

That's all. Now all that remains is the arithmetic. Good luck!