Table of contents

1. Matter and Measurements4h 31m
2. Atoms and the Periodic Table5h 23m
3. Ionic Compounds2h 18m
4. Molecular Compounds2h 18m
5. Classification & Balancing of Chemical Reactions3h 17m
6. Chemical Reactions & Quantities2h 27m
7. Energy, Rate and Equilibrium3h 46m
8. Gases, Liquids and Solids3h 25m
9. Solutions4h 10m
10. Acids and Bases3h 29m
11. Nuclear Chemistry56m
BONUS: Lab Techniques and Procedures1h 38m
BONUS: Mathematical Operations and Functions47m
12. Introduction to Organic Chemistry1h 34m
13. Alkenes, Alkynes, and Aromatic Compounds2h 12m
14. Compounds with Oxygen or Sulfur1h 6m
15. Aldehydes and Ketones1h 1m
16. Carboxylic Acids and Their Derivatives1h 11m
17. Amines39m
18. Amino Acids and Proteins1h 51m
19. Enzymes1h 37m
20. Carbohydrates1h 41m
21. The Generation of Biochemical Energy2h 8m
22. Carbohydrate Metabolism2h 22m
23. Lipids2h 26m
24. Lipid Metabolism1h 45m
25. Protein and Amino Acid Metabolism1h 37m
26. Nucleic Acids and Protein Synthesis2h 54m

9. Solutions

Osmolarity

GOB Chemistry

9. Solutions

Osmolarity

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5:10 minutes

Problem 84

Textbook Question

An isotonic solution must be approximately 0.30 osmol/L. How much KCl is needed to prepare 175 mL of an isotonic solution?

Verified step by step guidance

Step 1: Understand the concept of isotonic solutions. An isotonic solution has the same osmolarity as body fluids, which is approximately 0.30 osmol/L. Osmolarity is the total concentration of solute particles in a solution.

Step 2: Recognize that potassium chloride (KCl) dissociates completely in water into two ions: K⁺ and Cl⁻. Therefore, 1 mole of KCl produces 2 osmoles of particles. This means the osmolarity of the solution is twice the molarity of KCl.

Step 3: Use the formula for osmolarity: \( \text{Osmolarity} = \text{Molarity} \times \text{Number of particles per formula unit} \). Rearrange the formula to solve for molarity: \( \text{Molarity} = \frac{\text{Osmolarity}}{\text{Number of particles per formula unit}} \). Substitute \( \text{Osmolarity} = 0.30 \; \text{osmol/L} \) and \( \text{Number of particles per formula unit} = 2 \).

Step 4: Calculate the number of moles of KCl needed using the molarity formula: \( \text{Molarity} = \frac{\text{moles of solute}}{\text{volume of solution in liters}} \). Rearrange to solve for moles: \( \text{moles of solute} = \text{Molarity} \times \text{volume of solution in liters} \). Convert 175 mL to liters by dividing by 1000.

Step 5: Convert the moles of KCl to grams using the molar mass of KCl. The molar mass of KCl is approximately 74.55 g/mol. Use the formula: \( \text{mass of KCl} = \text{moles of KCl} \times \text{molar mass of KCl} \).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Osmolarity

Osmolarity is a measure of the total concentration of solute particles in a solution. It is expressed in osmoles per liter (osmol/L) and is crucial for understanding how solutions affect cell volume and function. An isotonic solution has the same osmolarity as body fluids, preventing net movement of water across cell membranes.

Isotonic Solutions

An isotonic solution is one that has the same osmotic pressure as another solution, typically bodily fluids. This means that when cells are placed in an isotonic solution, there is no net movement of water into or out of the cells, maintaining their shape and function. For human cells, an isotonic solution is approximately 0.30 osmol/L.

KCl Preparation

Potassium chloride (KCl) is often used to create isotonic solutions in laboratory settings. To prepare a specific osmolarity, one must calculate the amount of KCl needed based on its dissociation in solution. KCl dissociates into potassium (K+) and chloride (Cl-) ions, contributing to the total osmolarity, which must be considered when preparing the solution.

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