Chemistry Chapter on Ion Behavior

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Questions and Answers

Which ion is more likely to remain within the bulk medium due to its higher hydration?

Sodium ions

Hydronium ions (correct)

Chloride ions

Hydroxyl ions

What phenomenon describes the adsorption of ions on a surface?

Osmosis

Ion exchange

Electrical double layer (correct)

Electrophoresis

What happens to cations in this process?

They form precipitates with anions.

They are reduced to neutral atoms.

They remain dissolved in the solution.

They are adsorbed onto the surface of the particle. (correct)

What is the charge of the surface of the particle after cations are adsorbed?

Positive Signup and view all the answers

Why are hydronium ions favored to remain in bulk solutions compared to hydroxyl ions?

They are more hydrated Signup and view all the answers

Which of the following is NOT a characteristic of hydronium ions?

Less stable in solutions Signup and view all the answers

Which of the following describes the state of cations after they adsorb onto the particle's surface?

They become part of the particulate matter. Signup and view all the answers

Which of these ions is known to have a lower tendency to remain in the bulk medium compared to hydronium ions?

Hydroxyl ions Signup and view all the answers

What remains in the solution after cations are adsorbed?

Cations that were not adsorbed Signup and view all the answers

What does this region prevent in terms of particle interaction?

Particles from interacting at close distances Signup and view all the answers

How does the presence of electrolytes influence the primary maximum?

It decreases the magnitude of the primary maximum. Signup and view all the answers

What characteristic of electrolytes affects the primary maximum?

The presence and concentration of electrolytes Signup and view all the answers

Which of the following best describes the effect of electrolytes on particle behavior?

They alter particle charge distribution. Signup and view all the answers

What is a consequence of preventing particles from interacting at close distances?

Reduced likelihood of agglomeration Signup and view all the answers

What characterizes the primary minimum in the interaction between two particles?

It is a region of high attraction between particles. Signup and view all the answers

Which of the following does NOT describe the primary minimum?

It leads to increased distance between particles. Signup and view all the answers

In the context of particle interactions, what is likely to happen at the primary minimum?

Particles will strongly attract each other. Signup and view all the answers

What effect does the distance of separation have in the primary minimum region?

Decreasing distance increases attraction. Signup and view all the answers

Which statement is most relevant to understanding the primary minimum region?

It represents optimal position for bonding. Signup and view all the answers

Which functional groups can ionise as a function of pH in drug particles?

COOH and NH2 Signup and view all the answers

What property of drug particles is influenced by the ionisation of functional groups?

Solubility Signup and view all the answers

At which pH range would you expect the COOH group to be predominantly ionised?

Basic pH (above 7) Signup and view all the answers

Which of the following is a consequence of the ionisation of functional groups in drug particles?

Altered pharmacokinetics Signup and view all the answers

Which functional group is known for becoming protonated in acidic conditions?

NH2 Signup and view all the answers

What are particles located at the secondary minimum called?

Floccules Signup and view all the answers

What process is described as controlled flocculation?

Aggregation of particles at the secondary minimum Signup and view all the answers

How can the interaction between particles be disrupted?

By shaking Signup and view all the answers

What is a potential outcome of shaking floccules?

Accurate dosage removal Signup and view all the answers

Which term is associated with particles that are destabilized and can be viewed as clusters?

Floccules Signup and view all the answers

Study Notes

Pharmaceutical Suspension Stability

Pharmaceutical suspensions are inherently unstable.
Instability leads to sedimentation.
Instability leads to particle-particle interactions.
Instability leads to caking (compaction).

Zeta Potential and Stability

Most suspended particles in water acquire a charge.
The charge arises from specific adsorption of ions or ionization of ionizable surface groups (if present).
If charge arises from ionization, the particle's charge depends on the surrounding environment's pH.
Zeta potential measures the electrical potential difference between the surface of a particle and the surrounding solution.
Zeta potential is measured by electrophoretic mobility (movement of particles in an electric field).
Zeta potential is crucial for stability; high zeta potentials result in particle repulsion, preventing aggregation.

Electrokinetic Properties

Zeta potential is the difference between the tightly bound layer (shear plane) and the electroneutral region of the solution.

Interaction Between Particles

Interactions between particles in a liquid medium depend on the distance of separation.
Three states of interaction are possible:
- No interaction: Particles are far apart, a thermodynamically stable state.
- Coagulation (agglomeration): Particles come into close contact, forming an inseparable mass (cake). This is not desirable; the mixture can't be redispersed.
- Loose aggregation (floccules): Particles aggregate loosely and reversibly, forming flocs that can be redispersed by shaking. This is preferable.

Electrical Properties of Dispersed Particles

Within an aqueous medium, particles may acquire a charge.
This charging can be due to ionization of functional groups on the particle, or by adsorption of ions.
Ionization of groups like COOH or NH2 on insoluble particles depends on the pKa of the molecule and surrounding solution pH.
Adsorption of Ions: When electrolytes are present, ions can be adsorbed by the particles.
Preferential adsorption of hydroxyl (OH-) ions can occur in the absence of other electrolytes.

Adsorption of Ions

Immersion in an electrolyte solution can result in ion adsorption onto particle surfaces.
Absence of electrolytes leads to preferential adsorption of hydroxyl(OH−) ions.
These hydroxyl ions are more likely to remain within the bulk medium.
Adsorption of ions creates an electrical double layer.

Interaction Models

The DLVO theory explains the interaction between particles.
The theory accounts for attractive (van der Waals) forces and repulsive forces (electrical double layers).
The overall interaction energy (V_t) is the sum of attraction (V_a) and repulsion (V_r) energies: Vt = Va + Vr.

Interactions Regions

Three regions are distinguishable based on particle interaction energy and separation distance:
- Primary minimum: A region of strong attraction leading to coagulation.
- Primary maximum: A region of strong repulsion, opposing aggregation. Electrolyte concentration affects this region by decreasing the thickness and hence the strength of the electrical double layer of the particles.
- Secondary minimum: A region of weak attraction leading to flocculation; the aggregates can be broken apart by shaking.

Diagrammatic Representation

A diagram shows interaction energy versus separation distance, illustrating the three regions (primary minimum, primary maximum, secondary minimum).

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Description

Test your understanding of ion behavior in solutions with this quiz focusing on hydration, adsorption phenomena, and the interactions of cations with surfaces. Explore how these processes influence the stability of particles in different environments and the role of electrolytes. Perfect for reinforcing key concepts in chemistry.