Molality Worksheet Answer Key: Your Ultimate Guide!
Table of Contents :
Molality, a crucial concept in chemistry, is defined as the number of moles of solute per kilogram of solvent. It’s a measure that helps in determining the concentration of a solution, especially when temperature changes may cause variations in volume. In this guide, we'll explore everything you need to know about molality, provide a comprehensive worksheet, and discuss how to work with the answer key effectively. Let’s dive in! 📚
What is Molality?
Molality (denoted as m) is an important concentration unit that is particularly useful in physical chemistry. Unlike molarity, which is based on volume, molality is based on mass. This is critical because it provides a more accurate measurement when dealing with reactions that occur at varying temperatures and pressures.
Formula for Calculating Molality
The formula for calculating molality is straightforward:
[ \text{Molality (m)} = \frac{\text{moles of solute}}{\text{kilograms of solvent}} ]
Example Calculation
Let's say you dissolve 2 moles of sodium chloride (NaCl) in 1 kg of water. The molality would be:
[ m = \frac{2 , \text{moles}}{1 , \text{kg}} = 2 , \text{m} ]
Why Use Molality?
There are several reasons why chemists prefer to use molality over other concentration units:
- Independence from Temperature: Molality remains constant despite temperature changes since it’s based on mass, not volume.
- Useful in Colligative Properties: Molality is especially important in calculations involving colligative properties, such as boiling point elevation and freezing point depression.
- Simplicity in Preparation: It is easier to prepare solutions using mass measurements.
The Molality Worksheet
To reinforce your understanding of molality, we have prepared a worksheet that covers a variety of problems. Below is an outline of the types of questions you may encounter.
| Question Number | Description |
|---|---|
| 1 | Calculate the molality of a solution with 3 moles of KCl in 0.5 kg of water. |
| 2 | If 4 moles of glucose are dissolved in 2 kg of water, what is the molality? |
| 3 | Determine the molality of 5 moles of ethanol in 3 kg of solvent. |
| 4 | A solution is prepared by dissolving 0.5 moles of NaCl in 0.25 kg of water. Calculate its molality. |
| 5 | What is the molality of a solution if 10 moles of CaCl2 are in 5 kg of solvent? |
Answer Key to the Worksheet
Now, let’s provide the answers to the problems outlined in the worksheet.
Solutions to Worksheet Problems
-
Question 1:
- Calculation: [ m = \frac{3 , \text{moles}}{0.5 , \text{kg}} = 6 , \text{m} ]
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Question 2:
- Calculation: [ m = \frac{4 , \text{moles}}{2 , \text{kg}} = 2 , \text{m} ]
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Question 3:
- Calculation: [ m = \frac{5 , \text{moles}}{3 , \text{kg}} \approx 1.67 , \text{m} ]
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Question 4:
- Calculation: [ m = \frac{0.5 , \text{moles}}{0.25 , \text{kg}} = 2 , \text{m} ]
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Question 5:
- Calculation: [ m = \frac{10 , \text{moles}}{5 , \text{kg}} = 2 , \text{m} ]
Important Notes on Molality
"Remember, while calculating molality, it is essential to always use kilograms of solvent. Moles of solute can be determined using the molar mass of the substance."
Additional Practice Problems
To further sharpen your skills, consider these additional practice problems:
| Practice Question Number | Description |
|---|---|
| 1 | Find the molality of 0.75 moles of HCl in 0.5 kg of water. |
| 2 | Calculate the molality if 6 moles of NH4Cl are dissolved in 2 kg of water. |
| 3 | Determine the molality of a solution containing 2.5 moles of sugar in 1.5 kg of solvent. |
Conclusion
Understanding molality is essential for anyone studying chemistry. It provides a reliable way to express the concentration of solutions, regardless of the conditions they might be subjected to. Whether you are preparing for an exam or just looking to grasp the concept better, practicing with a worksheet can be an effective strategy. Remember to utilize the answer key to check your work and reinforce your understanding of this key topic. Happy studying! 🎉