Identify the atoms in the molecule

Oct 13, 2025 by wbrum.org 133 views

In chemistry, the molar mass of a molecule is a crucial property that helps us understand its composition and behavior. The molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). In this article, we will explore how to determine the molar mass of a molecule and apply this knowledge to solve a problem.

What is Molar Mass?

The molar mass of a molecule is the sum of the atomic masses of its constituent atoms. Atomic masses are typically expressed in units of atomic mass units (amu) or grams per mole (g/mol). To calculate the molar mass of a molecule, we need to know the atomic masses of its constituent atoms and multiply them by their respective numbers in the molecule.

Calculating Molar Mass: A Step-by-Step Guide

To calculate the molar mass of a molecule, follow these steps:

Identify the atoms in the molecule: Write down the chemical formula of the molecule and identify the atoms present in it.
Find the atomic masses of the atoms: Look up the atomic masses of the atoms present in the molecule in a periodic table or a reliable online resource.
Multiply the atomic masses by their respective numbers: Multiply the atomic mass of each atom by its number in the molecule.
Add up the products: Add up the products obtained in the previous step to get the molar mass of the molecule.

Applying the Concept to the Given Problem

Now that we have a clear understanding of how to calculate the molar mass of a molecule, let's apply this knowledge to the given problem.

We are given four molecules: $ \text{Al}_2(\text{SO}_4)_3 $, $ \text{Ca}(\text{NO}_3)_2 $, $ \text{Na}_2 \text{SO}_4 $, and $ \text{CuSO}_4 $. We need to determine which of these molecules has a molar mass of $342.14 \, \text{g/mol}$ .

Calculating the Molar Mass of Each Molecule

Let's calculate the molar mass of each molecule using the steps outlined above.

$ \text{Al}_2(\text{SO}_4)_3 $

Identify the atoms in the molecule: The molecule contains aluminum (Al), sulfur (S), and oxygen (O).
Find the atomic masses of the atoms: The atomic masses of Al, S, and O are 26.98 g/mol, 32.06 g/mol, and 16.00 g/mol, respectively.
Multiply the atomic masses by their respective numbers: Multiply the atomic mass of each atom by its number in the molecule.
- Al: 2 * 26.98 g/mol = 53.96 g/mol
- S: 3 * 32.06 g/mol = 96.18 g/mol
- O: 12 * 16.00 g/mol = 192.00 g/mol
Add up the products: Add up the products obtained in the previous step to get the molar mass of the molecule.
- Molar mass of $ \text{Al}_2(\text{SO}_4)_3 $ = 53.96 g/mol + 96.18 g/mol + 192.00 g/mol = 342.14 g/mol

$ \text{Ca}(\text{NO}_3)_2 $

Identify the atoms in the molecule: The molecule contains calcium (Ca), nitrogen (N), and oxygen (O).
Find the atomic masses of the atoms: The atomic masses of Ca, N, and O are 40.08 g/mol, 14.01 g/mol, and 16.00 g/mol, respectively.
Multiply the atomic masses by their respective numbers: Multiply the atomic mass of each atom by its number in the molecule.
- Ca: 1 * 40.08 g/mol = 40.08 g/mol
- N: 2 * 14.01 g/mol = 28.02 g/mol
- O: 6 * 16.00 g/mol = 96.00 g/mol
Add up the products: Add up the products obtained in the previous step to get the molar mass of the molecule.
- Molar mass of $ \text{Ca}(\text{NO}_3)_2 $ = 40.08 g/mol + 28.02 g/mol + 96.00 g/mol = 164.10 g/mol

$ \text{Na}_2 \text{SO}_4 $

Identify the atoms in the molecule: The molecule contains sodium (Na), sulfur (S), and oxygen (O).
Find the atomic masses of the atoms: The atomic masses of Na, S, and O are 22.99 g/mol, 32.06 g/mol, and 16.00 g/mol, respectively.
Multiply the atomic masses by their respective numbers: Multiply the atomic mass of each atom by its number in the molecule.
- Na: 2 * 22.99 g/mol = 45.98 g/mol
- S: 1 * 32.06 g/mol = 32.06 g/mol
- O: 4 * 16.00 g/mol = 64.00 g/mol
Add up the products: Add up the products obtained in the previous step to get the molar mass of the molecule.
- Molar mass of $ \text{Na}_2 \text{SO}_4 $ = 45.98 g/mol + 32.06 g/mol + 64.00 g/mol = 142.04 g/mol

$ \text{CuSO}_4 $

Identify the atoms in the molecule: The molecule contains copper (Cu), sulfur (S), and oxygen (O).
Find the atomic masses of the atoms: The atomic masses of Cu, S, and O are 63.55 g/mol, 32.06 g/mol, and 16.00 g/mol, respectively.
Multiply the atomic masses by their respective numbers: Multiply the atomic mass of each atom by its number in the molecule.
- Cu: 1 * 63.55 g/mol = 63.55 g/mol
- S: 1 * 32.06 g/mol = 32.06 g/mol
- O: 4 * 16.00 g/mol = 64.00 g/mol
Add up the products: Add up the products obtained in the previous step to get the molar mass of the molecule.
- Molar mass of $ \text{CuSO}_4 $ = 63.55 g/mol + 32.06 g/mol + 64.00 g/mol = 159.61 g/mol

Conclusion

Based on the calculations above, we can see that the molar mass of $ \text{Al}_2(\text{SO}_4)_3 $ is 342.14 g/mol, which matches the given value. Therefore, the correct answer is $ \text{Al}_2(\text{SO}_4)_3 $.

Key Takeaways

The molar mass of a molecule is the sum of the atomic masses of its constituent atoms.
To calculate the molar mass of a molecule, identify the atoms present in it, find their atomic masses, multiply them by their respective numbers, and add up the products.
The molar mass of a molecule is a crucial property that helps us understand its composition and behavior.

In our previous article, we explored the concept of molar mass and how to calculate it. We also applied this knowledge to solve a problem and determine which molecule has a molar mass of $342.14 \, \text{g/mol}$ . In this article, we will address some frequently asked questions related to molar mass and provide additional information to help you better understand this concept.

Q: What is the difference between atomic mass and molar mass?

A: The atomic mass of an element is the mass of a single atom of that element, typically expressed in units of atomic mass units (amu) or grams per mole (g/mol). The molar mass of a molecule, on the other hand, is the sum of the atomic masses of its constituent atoms, also expressed in units of g/mol.

Q: How do I calculate the molar mass of a molecule with multiple atoms of the same element?

A: To calculate the molar mass of a molecule with multiple atoms of the same element, you need to multiply the atomic mass of that element by the number of atoms present in the molecule. For example, if a molecule contains 3 atoms of carbon (C), you would multiply the atomic mass of C (12.01 g/mol) by 3 to get the total mass of C in the molecule.

Q: Can I use the molar mass of a molecule to determine its density?

A: Yes, you can use the molar mass of a molecule to determine its density. The density of a substance is defined as its mass per unit volume. By dividing the molar mass of a molecule by its volume, you can calculate its density.

Q: How do I calculate the volume of a molecule?

A: The volume of a molecule is typically calculated using the formula:

Volume = (number of atoms) * (atomic volume)

The atomic volume is a constant value that depends on the element. You can look up the atomic volume of an element in a reliable online resource or a chemistry textbook.

Q: Can I use the molar mass of a molecule to determine its boiling point?

A: Yes, you can use the molar mass of a molecule to determine its boiling point. The boiling point of a substance is a function of its intermolecular forces, which in turn depend on the mass of the molecules. By comparing the molar masses of different molecules, you can make predictions about their boiling points.

Q: How do I calculate the boiling point of a molecule?

A: The boiling point of a molecule is typically calculated using the formula:

Boiling point = (molar mass) * (intermolecular force constant)

The intermolecular force constant is a constant value that depends on the type of intermolecular force present in the molecule. You can look up the intermolecular force constant of an element in a reliable online resource or a chemistry textbook.

Q: Can I use the molar mass of a molecule to determine its solubility?

A: Yes, you can use the molar mass of a molecule to determine its solubility. The solubility of a substance is a function of its intermolecular forces, which in turn depend on the mass of the molecules. By comparing the molar masses of different molecules, you can make predictions about their solubilities.

Q: How do I calculate the solubility of a molecule?

A: The solubility of a molecule is typically calculated using the formula:

Solubility = (molar mass) * (intermolecular force constant)

Conclusion

In this article, we addressed some frequently asked questions related to molar mass and provided additional information to help you better understand this concept. We also explored how to calculate the density, boiling point, and solubility of a molecule using its molar mass. By following the steps outlined in this article, you can gain a deeper understanding of the properties of molecules and make predictions about their behavior.

Key Takeaways

The molar mass of a molecule is the sum of the atomic masses of its constituent atoms.
To calculate the molar mass of a molecule, identify the atoms present in it, find their atomic masses, multiply them by their respective numbers, and add up the products.
The molar mass of a molecule can be used to determine its density, boiling point, and solubility.
The density, boiling point, and solubility of a molecule are functions of its intermolecular forces, which in turn depend on the mass of the molecules.

By mastering the concept of molar mass and its applications, you can gain a deeper understanding of the properties of molecules and make predictions about their behavior.