Molality Worksheet Answer Key: Easy Solutions Inside!
Table of Contents :
Molality is a crucial concept in chemistry, particularly in solutions, as it helps chemists understand the concentration of solutes in solvents. This article provides an easy-to-follow guide on molality, including explanations, examples, and a worksheet answer key that will enhance your understanding and application of this topic. Let’s dive in! 🧪
What is Molality?
Molality (m) is defined as the number of moles of solute per kilogram of solvent. Unlike molarity, which is dependent on the volume of the solution, molality depends on the mass of the solvent, making it a more reliable measure in certain situations.
Formula for Molality
The formula to calculate molality is:
[ \text{Molality (m)} = \frac{\text{Moles of Solute}}{\text{Mass of Solvent (kg)}} ]
This relationship highlights how molality provides a clear perspective on the concentration of a solution, making it essential for various chemical calculations and experiments.
Why is Molality Important?
- Independent of Temperature 🌡️: Since molality is based on mass rather than volume, it remains unchanged with temperature variations.
- Useful for Colligative Properties: Colligative properties, such as boiling point elevation and freezing point depression, rely on the number of solute particles rather than their identity.
- Applications in Different Fields: Understanding molality is fundamental in fields like pharmaceuticals, environmental science, and chemical engineering.
Calculating Molality: Step-by-Step Process
To effectively calculate molality, follow these steps:
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Determine the moles of solute: Use the formula: [ \text{Moles} = \frac{\text{Mass of Solute (g)}}{\text{Molar Mass of Solute (g/mol)}} ]
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Measure the mass of the solvent: Make sure to convert grams to kilograms if necessary.
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Plug values into the molality formula: Once you have both moles of solute and mass of solvent, substitute them into the molality formula.
Example Calculation
Let's say we have 10 grams of sodium chloride (NaCl) dissolved in 500 grams of water.
Step 1: Calculate the moles of NaCl.
- Molar Mass of NaCl = 58.44 g/mol
- Moles of NaCl = ( \frac{10 , \text{g}}{58.44 , \text{g/mol}} \approx 0.171 , \text{moles} )
Step 2: Convert the mass of the solvent (water).
- Mass of water = 500 g = 0.500 kg
Step 3: Calculate molality.
- ( \text{Molality (m)} = \frac{0.171 , \text{moles}}{0.500 , \text{kg}} \approx 0.342 , \text{m} )
Summary Table of Calculation Steps
<table> <tr> <th>Step</th> <th>Details</th> </tr> <tr> <td>1</td> <td>Calculate moles of solute using mass and molar mass</td> </tr> <tr> <td>2</td> <td>Convert the mass of solvent to kilograms</td> </tr> <tr> <td>3</td> <td>Substitute values into the molality formula</td> </tr> </table>
Molality Worksheet
To practice calculating molality, you can create a worksheet with various problems that encourage the application of the concepts discussed. Here are a few sample questions:
- Calculate the molality of a solution made by dissolving 20 g of KCl in 1 kg of water.
- What is the molality of a solution containing 5 moles of glucose in 2 kg of solvent?
- If 15 g of sugar (C12H22O11) is dissolved in 750 g of water, find the molality.
Worksheet Answer Key
Here’s the answer key for the above worksheet:
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Question 1:
- Moles of KCl = ( \frac{20 , \text{g}}{74.55 , \text{g/mol}} \approx 0.268 , \text{moles} )
- Molality = ( \frac{0.268}{1} = 0.268 , \text{m} )
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Question 2:
- Molality = ( \frac{5 , \text{moles}}{2 , \text{kg}} = 2.5 , \text{m} )
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Question 3:
- Molar Mass of C12H22O11 = 342.30 g/mol
- Moles = ( \frac{15 , \text{g}}{342.30 , \text{g/mol}} \approx 0.044 , \text{moles} )
- Mass of water = 0.750 kg
- Molality = ( \frac{0.044}{0.750} \approx 0.059 , \text{m} )
Tips for Success in Molality Calculations
- Always double-check your measurements: Accurate measurements of solute and solvent are crucial for correct calculations.
- Practice makes perfect: The more problems you solve, the more comfortable you will become with the calculations.
- Understand the concepts: Having a solid understanding of molarity vs. molality, and the factors affecting solutions will deepen your knowledge and improve your application skills.
Understanding molality and mastering its calculations is essential for anyone venturing into chemistry. With the knowledge from this guide, you will be well-equipped to handle molality calculations confidently. Happy learning! 🎉