1. Calculate the molar mass of a vapor that has a density of 1.58 g/L at 23.2 oC

Question

1. Calculate the molar mass of a vapor that has a density of 1.58 g/L at 23.2 oC and 610. torr. 2. If the volume of a container is 39.4 L. and the container holds a gas at 13.2 oC. and 7.00x104 torr. The density of the gas is 16.88 g/L. a) What mass of gas (in kg.) does the container hold? b) What is the molar mass of the gas? 3. If the volume of the cylinder is 5500 mL and the pressure of the O2 in it is 2.5 atm. (temperature is 25oC) a. How many moles of oxygen molecules are in the cylinder? b. How many grams of oxygen are in the cylinder?

Explanation / Answer

we would need to know the temperature to solve for this, but assume we are at or near room temp of 300K

you use the equation:

PV = nRT

where the symbols have the usual meaning in the perfect gas law

solve for n:

n=PV/RT

and the real trick in solving this will be using a consistent set of units

if you useatmand liters, then the value of R to use is 0.082L atm/mol K

using P=105 atm, V=0.625L, T=300 and R=0.082, you can find a value of n

this will tell you how many moles are in the sample; then, just multiply the number of moles by Avogardro's number to get the number of molecules in the cylinder

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