# Calculating Density of Oxygen at STP

• tomrh3
In summary, the ideal gas law, PV=nRT, can be used to find the density of an element at STP. To do so, you need to account for the number of moles, n, which can be calculated using the element's atomic mass. In the case of oxygen, n=2 since it consists of 2 atoms at STP. The molar volume at STP is 22.4141L and the density can be calculated by dividing the molar mass by the molar volume. It is important to use the correct units for R in the ideal gas law.
tomrh3
Ok, I know I have to use the ideal gas law, but am not exactly sure how to apply that to finding the density.

PV=nRT (ideal gas law)

1atm (volume) = n(number of moles - can I just use 1 for ease?)(8.315 J(mol•K) (temperature)

Not quite sure where to go from here, any help would be appreciated just to get me in the right direction. Do I need the density of Oxygen at another temperature in order to do this?

Tom,
density of an element at stp is its mass/volume.
Since-breathable- oxygen is 2 atoms at standard temp(293-298K) and pressure(1atm), you need to account for O2-- 16 grams per mole, i.e., n=2.
Do you have the "unit" volume?
nrt/p = V.
you can get its atomic mass from the periodic chart.
A decent (one bought from the college bookstore for \$5.00) chart would also have the unit density on it as well.

SteveDB said:
Tom,
Since-breathable- oxygen is 2 atoms at standard temp(293-298K) and pressure(1atm), you need to account for O2-- 16 grams per mole, i.e., n=2.
Do you have the "unit" volume?
nrt/p = V.

Shortly after my post I realized that the atomic mass was the piece that I was missing, so to find n I did n=(mass)/(molecular mass), n=1gram/16, and after plugging that all in, I got a final density of 1.40 (which is basically much that of oxygen). Was I right to use n=1/16 or was it n=2? Thanks for the help.

The molar volume at stp is 22.4141L as I recall. This is easily calculated with the ideal gas law using 1 mole and stp, be sure to use correct units for your R. From there the density will be molar mass/molar volume.

I found this claculation by chance and I noticed a mistake. Molecular mass for O2 is 32, not 16 because the O2 molecule is formed by two O atoms which mass is 16 each.

## 1. What is the formula for calculating the density of oxygen at STP?

The formula for calculating the density of oxygen at STP (Standard Temperature and Pressure) is:

Density = mass/volume = (P x M) / (R x T)

Where P is the pressure (1 atm), M is the molar mass of oxygen (32 g/mol), R is the gas constant (0.0821 L atm/mol K), and T is the temperature (273 K).

## 2. What is the value of STP and why is it important?

STP (Standard Temperature and Pressure) is a set of standard conditions used for measuring and comparing properties of gases. It is defined as a temperature of 273 K (0°C) and a pressure of 1 atm (101.3 kPa). This value is important because it allows for consistent and accurate measurements and calculations in the study of gases.

## 3. How do you determine the molar mass of oxygen?

The molar mass of oxygen can be determined by adding up the atomic weights of all the elements in its chemical formula, which is O2. Oxygen has an atomic weight of 16.00 g/mol, so the molar mass of oxygen is 2 x 16.00 = 32.00 g/mol.

## 4. Can the density of oxygen at STP vary?

No, the density of oxygen at STP is a constant value and does not vary. This is because STP is a set of standard conditions, and as long as those conditions are met, the density of oxygen will always be the same.

## 5. How does the density of oxygen at STP compare to other gases?

The density of oxygen at STP is approximately 1.429 g/L. This is similar to the density of other gases at STP, such as nitrogen (1.250 g/L) and carbon dioxide (1.977 g/L). However, the density of oxygen is slightly lower than the density of helium (0.1785 g/L) and higher than the density of hydrogen (0.0899 g/L) at STP.

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