Calculating the Mass of 120 cm3 of Oxygen at STP

To find the mass of 120 cm3 of oxygen gas (O2) at standard temperature and pressure (STP), we can use the ideal gas law and the molar volume of a gas at STP. This article will walk you through the steps to calculate the mass accurately.

Key Facts

At STP (0°C and 1 atm), 1 mole of any ideal gas occupies 22.4 liters (or 22400 cm3). The molar mass of oxygen (O2) is approximately 32 g/mol.

Steps to Calculate Mass

Convert cm3 to liters:

120 cm3 0.120 liters

Calculate the number of moles of O2:

Moles of O2 Volume / Molar Volume 0.120 liters / 22.4 liters/mol ≈ 0.00536 moles

Calculate the mass of O2:

Mass Moles × Molar Mass 0.00536 moles × 32 g/mol ≈ 0.1715 grams

Conclusion

The mass of 120 cm3 of oxygen at STP is approximately 0.1715 grams.

Are You Struggling with Your Homework?

If these problems are part of your homework, it's important to work through them to ensure you understand the concepts. Simply substituting values blindly without understanding the underlying principles is not a productive study method. Engage with the material actively to promote true learning.

It's essential to understand the relationships between different physical quantities and how they affect each other. This knowledge can be applied not only to chemistry but also to various other scientific fields. So, take the time to learn and practice these calculations, and don't hesitate to seek help if needed.

Verification Using the Ideal Gas Law

To verify the calculation using the ideal gas law (PV nRT), let's go through the steps:

P 1.00 atm (standard pressure), T 273.15 K (standard temperature), a mole of gas occupies 22.4 liters (molar volume at STP).

Now, convert 120 cm3 to liters:

120 cm3 120 mL 0.120 L

Using the ideal gas law:

V/n RT/P 22.4 L/mol

Calculate the moles of O2:

Moles of O2 V / 22.4 L/mol 0.120 L / 22.4 L/mol 0.00536 moles

Calculate the mass of O2:

Mass Moles × Molar Mass 0.00536 moles × 32 g/mol 0.171 grams

The result confirms that the mass of 120 cm3 of oxygen at STP is approximately 0.171 grams.