Textbook Question
When 9.12 g of HCl was dissolved in 190 g of water, the freezing point of the solution was - 4.65 °C. What is the value of the van't Hoff factor for HCl?
Ch.13 - Solutions & Their Properties
McMurry8th EditionChemistryISBN: 9781292336145
Not the one you use?Change textbookSelect a different textbook
Table of contents
- Ch.1 - Chemical Tools: Experimentation & Measurement170
- Ch.2 - Atoms, Molecules & Ions160
- Ch.3 - Mass Relationships in Chemical Reactions169
- Ch.4 - Reactions in Aqueous Solution199
- Ch.5 - Periodicity & Electronic Structure of Atoms102
- Ch.6 - Ionic Compounds: Periodic Trends and Bonding Theory92
- Ch.7 - Covalent Bonding and Electron-Dot Structures61
- Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure59
- Ch.9 - Thermochemistry: Chemical Energy122
- Ch.10 - Gases: Their Properties & Behavior155
- Ch.11 - Liquids & Phase Changes54
- Ch.12 - Solids and Solid-State Materials73
- Ch.13 - Solutions & Their Properties120
- Ch.14 - Chemical Kinetics98
- Ch.15 - Chemical Equilibrium125
- Ch.16 - Aqueous Equilibria: Acids & Bases110
- Ch.17 - Applications of Aqueous Equilibria147
- Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium86
- Ch.19 - Electrochemistry154
- Ch.20 - Nuclear Chemistry96
- Ch.21 - Transition Elements and Coordination Chemistry156
- Ch.22 - The Main Group Elements187
- Ch.23 - Organic and Biological Chemistry51
Chapter 13, Problem 101
A solution concentration must be expressed in molality when considering boiling-point elevation or freezing-point depression but can be expressed in molarity when consider- ing osmotic pressure. Why?
Verified step by step guidance1
Understand the definitions: Molality (m) is defined as the number of moles of solute per kilogram of solvent, whereas Molarity (M) is defined as the number of moles of solute per liter of solution.
Recognize the dependency on temperature: Molality is independent of temperature because it is based on the mass of the solvent, which does not change with temperature. Molarity, however, can change with temperature as the volume of the solution expands or contracts.
Apply to boiling-point elevation and freezing-point depression: These colligative properties depend on the number of particles in a solution and are influenced by temperature changes. Using molality ensures that the concentration remains constant regardless of temperature changes.
Consider osmotic pressure: Osmotic pressure is a colligative property that depends on the concentration of solute particles in a solution. Since osmotic pressure measurements are typically conducted at constant temperature, molarity can be used as it directly relates to the volume of the solution.
Summarize the relevance of concentration units: Choosing the appropriate unit of concentration (molality or molarity) depends on the property being measured and how it is affected by temperature changes. Molality is used for temperature-dependent properties to ensure consistency, while molarity is suitable for properties measured at constant temperatures.
Verified video answer for a similar problem:
This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
2mWas this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Molality vs. Molarity
Molality (m) is defined as the number of moles of solute per kilogram of solvent, while molarity (M) is the number of moles of solute per liter of solution. Molality is temperature-independent, making it more suitable for colligative properties like boiling-point elevation and freezing-point depression, which depend on the mass of the solvent rather than the volume of the solution.
Recommended video:
Guided course
00:40
Molality
Colligative Properties
Colligative properties are physical properties of solutions that depend on the number of solute particles in a given amount of solvent, not the identity of the solute. Boiling-point elevation and freezing-point depression are examples of colligative properties, where the addition of solute alters the solvent's boiling and freezing points based on the concentration of solute particles.
Recommended video:
Guided course
01:26Colligative Properties
Osmotic Pressure
Osmotic pressure is the pressure required to prevent the flow of solvent into a solution through a semipermeable membrane. It is directly proportional to the molarity of the solute in the solution, making molarity a suitable measure for osmotic pressure calculations. This relationship arises because osmotic pressure depends on the concentration of solute particles in the solution, which is effectively represented by molarity.
Recommended video:
Guided course
01:13Osmotic Pressure Formula