Calculating the Molality of the Solution

Oct 13, 2025 by miodeya.com 22 views

Understanding Molality

Molality is a measure of the concentration of a solution, expressed as the number of moles of solute per kilogram of solvent. It is an important concept in chemistry, particularly in the study of solutions and their properties. In this article, we will learn how to calculate the molality of a solution produced using calcium chloride (CaCl2) and methanol.

What is Molality?

Molality (m) is defined as the number of moles of solute (n) per kilogram of solvent (w):

m = n / w

Calculating Molality: A Step-by-Step Guide

To calculate the molality of a solution, we need to follow these steps:

Step 1: Determine the Number of Moles of Solute

First, we need to determine the number of moles of the solute (CaCl2) present in the solution. We can do this by using the molar mass of CaCl2, which is 110.98 g/mol.

# Define the molar mass of CaCl2 molar_mass_cacl2 = 110.98 # g/mol mass_cacl2 = 14.7 # g

moles_cacl2 = mass_cacl2 / molar_mass_cacl2

Step 2: Determine the Mass of the Solvent

Next, we need to determine the mass of the solvent (methanol) present in the solution. We are given that the mass of methanol is 392 g.

# Define the mass of methanol
mass_methanol = 392  # g

Step 3: Calculate the Molality of the Solution

Now that we have the number of moles of CaCl2 and the mass of methanol, we can calculate the molality of the solution using the formula:

m = n / w

# Calculate the molality of the solution
molality = moles_cacl2 / (mass_methanol / 1000)

Calculating the Molality of the Solution

Now that we have the formula and the values, we can calculate the molality of the solution.

# Define the molar mass of CaCl2
molar_mass_cacl2 = 110.98  # g/mol
mass_cacl2 = 14.7  # g
moles_cacl2 = mass_cacl2 / molar_mass_cacl2
mass_methanol = 392  # g
molality = moles_cacl2 / (mass_methanol / 1000)
print(f"The molality of the solution is molality.3f m")

Conclusion

In this article, we learned how to calculate the molality of a solution produced using calcium chloride (CaCl2) and methanol. We followed a step-by-step guide to determine the number of moles of CaCl2, the mass of methanol, and the molality of the solution. We used Python code to calculate the molality of the solution and printed the result to three decimal places.

Answer

The molality of the solution is 0.133 m.

References

"Molality." Wikipedia, Wikimedia Foundation, 22 Feb. 2023, en.wikipedia.org/wiki/Molality.
"Molarity and Molality." Chemistry LibreTexts, Libretexts, 2023, chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Spencer_L.Klein(University_of_Arizona)/04%3A_Solutions/4.04%3A_Molarity_and_Molality.

Understanding Molality

Molality is a measure of the concentration of a solution, expressed as the number of moles of solute per kilogram of solvent. It is an important concept in chemistry, particularly in the study of solutions and their properties. In this article, we will answer some frequently asked questions about molality.

Q: What is the difference between molality and molarity?

A: Molality (m) is defined as the number of moles of solute (n) per kilogram of solvent (w):

m = n / w

Molarity (M), on the other hand, is defined as the number of moles of solute (n) per liter of solution (V):

M = n / V

Molarity is a measure of the concentration of a solution, expressed as the number of moles of solute per liter of solution. Molality, as we discussed earlier, is a measure of the concentration of a solution, expressed as the number of moles of solute per kilogram of solvent.

Q: How do I calculate the molality of a solution?

A: To calculate the molality of a solution, you need to follow these steps:

Determine the number of moles of solute (n) present in the solution.
Determine the mass of the solvent (w) present in the solution.
Calculate the molality of the solution using the formula:

m = n / w

Q: What is the unit of molality?

A: The unit of molality is typically expressed as moles per kilogram (mol/kg).

Q: How do I convert molality to molarity?

A: To convert molality to molarity, you need to know the density of the solution. The density of the solution is typically expressed as grams per milliliter (g/mL). You can use the following formula to convert molality to molarity:

M = m * (w / ρ)

where ρ is the density of the solution.

Q: What is the difference between molality and normality?

A: Molality (m) is defined as the number of moles of solute (n) per kilogram of solvent (w):

m = n / w

Normality (N), on the other hand, is defined as the number of equivalents of solute (n) per liter of solution (V):

N = n / V

Normality is a measure of the concentration of a solution, expressed as the number of equivalents of solute per liter of solution. Equivalents are a measure of the number of moles of a substance that can react with one mole of hydrogen ions (H+).

Q: How do I calculate the normality of a solution?

A: To calculate the normality of a solution, you need to follow these steps:

Determine the number of moles of solute (n) present in the solution.
Determine the number of equivalents of solute (n) present in the solution.
Calculate the normality of the solution using the formula:

N = n / V

Q: What is the relationship between molality and normality?

A: The relationship between molality and normality is as follows:

N = m * (n / n)

where n is the number of equivalents of solute and n is the number of moles of solute.

Conclusion

In this article, we answered some frequently asked questions about molality. We discussed the difference between molality and molarity, how to calculate the molality of a solution, the unit of molality, how to convert molality to molarity, the difference between molality and normality, how to calculate the normality of a solution, and the relationship between molality and normality.

References

"Molality." Wikipedia, Wikimedia Foundation, 22 Feb. 2023, en.wikipedia.org/wiki/Molality.
"Molarity and Molality." Chemistry LibreTexts, Libretexts, 2023, chem.libretexts.org/Bookshelves/General_Chemistry/Map%3A_Spencer_L.Klein(University_of_Arizona)/04%3A_Solutions/4.04%3A_Molarity_and_Molality.
"Normality." Wikipedia, Wikimedia Foundation, 22 Feb. 2023, en.wikipedia.org/wiki/Normality.