Colligative Properties Worksheet Answer Key Explained
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In the world of chemistry, understanding colligative properties is crucial for grasping how solutes affect the properties of solvents. This knowledge is often assessed through worksheets that help students apply their understanding in practical ways. In this article, we will break down the key concepts associated with colligative properties, their definitions, and how to interpret an answer key from a colligative properties worksheet effectively.
What Are Colligative Properties? 🔍
Colligative properties are properties of solutions that depend on the number of solute particles in a given quantity of solvent, rather than the identity of the solute. There are four main types of colligative properties:
- Vapor Pressure Lowering: The presence of solute particles decreases the vapor pressure of a solvent.
- Boiling Point Elevation: A solution will boil at a higher temperature than the pure solvent due to the presence of solute particles.
- Freezing Point Depression: A solution will freeze at a lower temperature than the pure solvent.
- Osmotic Pressure: This is the pressure required to stop the flow of solvent into the solution through a semipermeable membrane.
Key Formulas to Remember 📚
Understanding the calculations behind colligative properties is essential for solving problems on worksheets. Here are some key formulas:
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Boiling Point Elevation: [ \Delta T_b = i \cdot K_b \cdot m ]
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Freezing Point Depression: [ \Delta T_f = i \cdot K_f \cdot m ]
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Osmotic Pressure: [ \Pi = i \cdot C \cdot R \cdot T ]
Where:
- ( \Delta T ) is the change in temperature (boiling or freezing point),
- ( i ) is the van 't Hoff factor (the number of particles the solute breaks into),
- ( K_b ) and ( K_f ) are the ebullioscopic and cryoscopic constants, respectively,
- ( m ) is the molality of the solution,
- ( \Pi ) is the osmotic pressure,
- ( C ) is the molarity of the solution,
- ( R ) is the ideal gas constant,
- ( T ) is the temperature in Kelvin.
Example Problems 🧪
When working on a colligative properties worksheet, you might encounter various types of problems. Below are some examples with their explanations.
Example 1: Boiling Point Elevation 🌡️
Problem: Calculate the boiling point of a solution containing 2.5 moles of NaCl in 1 kg of water. (Assume ( K_b ) for water is 0.512 °C kg/mol and ( i = 2 ) for NaCl)
Solution:
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Calculate ( \Delta T_b ): [ \Delta T_b = i \cdot K_b \cdot m ] First, find molality ( m ): [ m = \frac{\text{moles of solute}}{\text{kg of solvent}} = \frac{2.5 , \text{mol}}{1 , \text{kg}} = 2.5 , \text{mol/kg} ]
Now plug in the values: [ \Delta T_b = 2 \cdot 0.512 \cdot 2.5 = 2.56 , °C ]
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Add this to the normal boiling point of water (100 °C): [ 100 + 2.56 = 102.56 , °C ]
Example 2: Freezing Point Depression ❄️
Problem: What is the freezing point of a solution containing 1.5 moles of glucose (C6H12O6) in 1 kg of water? (Assume ( K_f ) for water is 1.86 °C kg/mol and ( i = 1 ) for glucose)
Solution:
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Calculate ( \Delta T_f ): [ \Delta T_f = i \cdot K_f \cdot m ] First, find molality ( m ): [ m = \frac{1.5 , \text{mol}}{1 , \text{kg}} = 1.5 , \text{mol/kg} ]
Now plug in the values: [ \Delta T_f = 1 \cdot 1.86 \cdot 1.5 = 2.79 , °C ]
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Subtract this from the normal freezing point of water (0 °C): [ 0 - 2.79 = -2.79 , °C ]
Answer Key Interpretation 📝
When reviewing an answer key from a colligative properties worksheet, it's essential to interpret the answers accurately. Here are a few tips:
- Check for Units: Ensure that answers are given with the correct units (°C, mol/kg, atm, etc.).
- Look for Explanations: Many answer keys provide explanations for the solutions. Use these to understand the underlying concepts better.
- Compare Steps: Ensure that the steps you took in your calculations align with those in the answer key. This is crucial for identifying where you might have gone wrong.
Important Notes 💡
“Understanding the logic behind colligative properties and how they impact the physical characteristics of solutions is key for success in chemistry.”
By mastering the concepts of colligative properties and utilizing the resources available, including worksheets and answer keys, you can enhance your understanding and problem-solving skills in chemistry. Regular practice with problems and interpretation of solutions will make these principles second nature.
Conclusion
Colligative properties are vital in the study of solutions and their behaviors. Understanding these concepts allows students and professionals alike to predict how different solutes affect solvent properties. By engaging with worksheets and answer keys, learners can solidify their grasp on these important chemical principles and prepare effectively for exams and real-world applications.