Chemistry: Dissolution and Diffusion Principles

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Questions and Answers

What is the primary factor that colligative properties depend on?

The size of the solvent molecules

The temperature of the solution

The identity of the solute

The concentration of the solute molecules (correct)

Which of the following is NOT a colligative property?

Boiling point elevation

Density of the solution (correct)

Freezing point depression

Vapor pressure lowering

How does an increase in solute concentration affect the vapor pressure of a solution?

It decreases the vapor pressure (correct)

It has no effect on the vapor pressure

It causes vapor pressure to fluctuate randomly

It increases the vapor pressure

Which of the following colligative properties would result from adding a non-volatile solute to a solvent?

Lowering of the vapor pressure Signup and view all the answers

What does the term 'colligative properties' imply about a solution?

They are influenced by the total number of solute particles Signup and view all the answers

What defines colligative properties in solutions?

They depend on the concentration of solute particles only. Signup and view all the answers

Which of the following is a characteristic of colligative properties?

They involve changes in boiling point and freezing point. Signup and view all the answers

Which application does NOT involve colligative properties?

Adding sugar to enhance flavor in drinks. Signup and view all the answers

Which factor will NOT influence the colligative properties of a solution?

The chemical nature of the solute particles. Signup and view all the answers

How would increasing the concentration of a non-volatile solute affect the vapor pressure of a solution?

It would decrease the vapor pressure. Signup and view all the answers

Which of the following best defines colligative properties of a solution?

Properties that depend on the quantity of solute particles in a solution. Signup and view all the answers

Which of the following is NOT considered a colligative property?

Density of the solution Signup and view all the answers

How does the addition of a solute affect the freezing point of a solution?

It decreases the freezing point. Signup and view all the answers

Which of the following statements is true regarding boiling point elevation caused by solutes?

Boiling point elevation is directly proportional to the concentration of solute particles. Signup and view all the answers

What effect do colligative properties have on the osmotic pressure of a solution?

They increase the osmotic pressure with a higher concentration of solute particles. Signup and view all the answers

Study Notes

Dissolution

Dissolution is the process of a solid solute entering a solution when added to a suitable solvent.
Dissolution rate is the speed at which the solid dissolves.
Dissolution is a crucial step in the absorption of solid drugs from tablets or capsules.
Key steps include disintegration, dissolution, and absorption.
Dissolution is the rate-limiting step in drug absorption.
Dissolution of solids in a liquid happens in two stages:
- Interfacial reaction: releasing solute molecules from the solid phase.
- Migration: solute molecules move through boundary layers into the bulk solution through diffusion or convection.

Diffusion

Diffusion is the spontaneous movement of solute molecules from a high concentration region to a low concentration region.
The driving force is the concentration gradient (chemical potential); it continues until uniform concentration.
Passage through barriers occurs via:
- Simple molecular diffusion (permeation): involves dissolution of the solute in the bulk membrane.
- Movement through pores and channels: solute molecules pass through solvent-filled pores in the membrane.

Fick's First Law of Diffusion

The rate of diffusion is proportional to the concentration gradient.
$$ Jx = -D \frac{dc}{dx} $$
J: is the flux of the diffused component (amount/time).
D: is the diffusion coefficient (constant at a given temperature for a particular system).
dc/dx: is the concentration gradient. The negative sign indicates that diffusion occurs in the direction opposite to the high concentration.

Drug Transport in Biological Systems

Drugs pass through living membranes via passive or active transport.
Passive transport: simple diffusion from high to low concentration (e.g., in the gastrointestinal tract).
Active transport: drug molecules transported across the membrane with the help of a biological carrier, possibly against the concentration gradient.

Fick's Second Law of Diffusion

Describes the rate of change of concentration with time in a specific region.
Steady state is reached when the rate of change of concentration is zero in the system.
This happens from the donor to the receptive part of the system.

Rate of Drug Transport

Drug transport is affected by:
- Physicochemical properties of the drug.
- Nature of the membrane.
- Concentration across the membrane.
Drugs can exist as ionized or non-ionized forms.
Ionization depends on the drug's pKa value and the pH of the medium, described by the Henderson-Hasselbalch equation.

Percutaneous Absorption

Percutaneous absorption of topically applied drugs (ointments, creams, etc.) occurs in three steps:
- Dissolution of drug in the vehicle.
- Diffusion of dissolved drug from the vehicle to the skin surface.
- Penetration of drug molecules through the skin layer.
The slowest step (penetration usually) is the rate-limiting step for absorption.

Biopharmaceutics Classification System (BCS)

Classifies drugs based on their solubility and intestinal permeability.
Four classes:
- Class I: High solubility, high permeability (e.g., deltiazem, propranolol)
- Class II: Low solubility, high permeability (e.g., diclofenac, naproxen)
- Class III: High solubility, low permeability (e.g., famotidine, cimetidine)
- Class IV: Low solubility, low permeability (e.g., furosemide, chlorthiazide)

Colligative Properties of Solutions

Properties that depend on the concentration of solute particles, not the kind of solute.
Includes:
- Osmotic pressure
- Vapor pressure lowering
- Boiling point elevation
- Freezing point depression

Osmotic Pressure

The external pressure needed to prevent solvent entry (osmosis) into a solution through a semi-permeable membrane.
If two solutions have different concentrations and separated by a semipermeable membrane, solvent moves from the lower-to higher-solute-concentration solution.
Osmotic pressure depends on the concentration of solute particles (number of moles per unit volume).

Vapor Pressure Lowering

When a non-volatile solute is dissolved in a liquid solvent, the solvent's vapor pressure decreases.
This is because some solvent surface molecules are replaced by solute molecules, thus reduced area.

Boiling Point Elevation

The boiling point of a solution is higher than the boiling point of the pure solvent. This is due to vapor pressure lowering.
The solution needs a higher temperature to achieve the same vapor pressure as the atmospheric pressure.

Freezing Point Depression

The freezing point of a solution is lower than the freezing point of the pure solvent due to vapor-pressure lowering.
This phenomenon is used in antifreeze applications or in ice cream production (ice/salt mixture).

Determination of Colligative Properties

The change in freezing and boiling points are proportional to the molal concentration of solute.
These relationships are used to calculate molar weights of substances. (Equations available in the text).

Practical Applications of Colligative Properties

Preparation of isotonic solutions (intravenous, lachrymal).
Determination of the molecular weight of solutes.
Experimental physiology (e.g., tissue immersion).

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Description

This quiz explores the concepts of dissolution and diffusion in chemistry. Understand the processes by which solid solutes enter solutions, the factors affecting dissolution rates, and how diffusion works across concentration gradients. Perfect for students looking to grasp these fundamental chemical principles.