Calculating Mass from Volume

Oct 13, 2025 by wbrum.org 17 views

Introduction

In chemistry, understanding the relationship between the mass and volume of a substance is crucial for various calculations, including determining the number of moles present in a given amount of a substance. In this article, we will explore how to calculate the number of moles of oxygen gas (O2) present in 281 mL, given the density of O2 as 1.33 g/L.

Understanding Density

Density is defined as the mass per unit volume of a substance. Mathematically, it can be expressed as:

Density (ρ) = Mass (m) / Volume (V)

In this case, the density of O2 is given as 1.33 g/L. This means that for every liter of O2, the mass is 1.33 grams.

Calculating Mass from Volume

To calculate the mass of O2 present in 281 mL, we need to first convert the volume from milliliters (mL) to liters (L). Since 1 L = 1000 mL, we can convert 281 mL to liters as follows:

281 mL = 0.281 L

Now, we can use the formula for density to calculate the mass of O2 present in 0.281 L:

Mass (m) = Density (ρ) x Volume (V)

Substituting the values, we get:

m = 1.33 g/L x 0.281 L m = 0.37373 g

Calculating Number of Moles

The number of moles of a substance can be calculated using the formula:

Number of Moles (n) = Mass (m) / Molar Mass (M)

The molar mass of O2 is 32 g/mol. Substituting the values, we get:

n = 0.37373 g / 32 g/mol n = 0.01167 mol

Expressing Answer to 3 Significant Figures

To express the answer to 3 significant figures, we round the number of moles to 0.0117 mol.

Conclusion

In this article, we calculated the number of moles of oxygen gas (O2) present in 281 mL, given the density of O2 as 1.33 g/L. We first converted the volume from milliliters to liters, then calculated the mass of O2 present in 0.281 L using the formula for density. Finally, we calculated the number of moles of O2 using the formula: Number of Moles (n) = Mass (m) / Molar Mass (M). The result is 0.0117 mol.

Additional Information

The density of a substance is a measure of its mass per unit volume.
The molar mass of a substance is the mass of one mole of that substance.
The number of moles of a substance can be calculated using the formula: Number of Moles (n) = Mass (m) / Molar Mass (M).

References

[1] CRC Handbook of Chemistry and Physics, 97th Edition.
[2] IUPAC, Compendium of Chemical Terminology, 2nd Edition.

Introduction

Calculating the number of moles of a substance from its volume and density is a fundamental concept in chemistry. In our previous article, we explored how to calculate the number of moles of oxygen gas (O2) present in 281 mL, given the density of O2 as 1.33 g/L. In this article, we will address some frequently asked questions (FAQs) related to this topic.

Q: What is the formula for calculating the number of moles from volume and density?

A: The formula for calculating the number of moles from volume and density is:

Number of Moles (n) = (Mass (m) / Molar Mass (M))

However, if you know the density of the substance, you can first calculate the mass using the formula:

Mass (m) = Density (ρ) x Volume (V)

Then, you can calculate the number of moles using the formula:

Number of Moles (n) = Mass (m) / Molar Mass (M)

Q: How do I convert milliliters (mL) to liters (L)?

A: To convert milliliters (mL) to liters (L), you can divide the volume in milliliters by 1000. For example, to convert 281 mL to liters, you can divide 281 by 1000:

281 mL = 0.281 L

Q: What is the molar mass of oxygen gas (O2)?

A: The molar mass of oxygen gas (O2) is 32 g/mol.

Q: How do I calculate the mass of a substance from its volume and density?

A: To calculate the mass of a substance from its volume and density, you can use the formula:

Mass (m) = Density (ρ) x Volume (V)

Q: What is the significance of significant figures in scientific calculations?

A: Significant figures are a way to express the precision of a measurement. In scientific calculations, it is essential to round the answer to the correct number of significant figures. In this article, we rounded the number of moles to 3 significant figures.

Q: Can I use this method to calculate the number of moles of any substance?

A: Yes, you can use this method to calculate the number of moles of any substance, provided you know its density and molar mass.

Q: What are some common sources of error in calculating the number of moles from volume and density?

A: Some common sources of error in calculating the number of moles from volume and density include:

Rounding errors: Rounding errors can occur when converting between units or when calculating the number of moles.
Measurement errors: Measurement errors can occur when measuring the volume or density of a substance.
Unit errors: Unit errors can occur when using the wrong units or when converting between units.

Conclusion

In this article, we addressed some frequently asked questions (FAQs) related to calculating the number of moles from volume and density. We hope this article has provided you with a better understanding of this fundamental concept in chemistry.

Additional Information

[1] CRC Handbook of Chemistry and Physics, 97th Edition.
[2] IUPAC, Compendium of Chemical Terminology, 2nd Edition.