Chemistry: Adsorption and Absorption

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Questions and Answers

What characteristic of pyrogens influences their adsorption behavior on adsorbents?

Color and appearance

High molecular weight (correct)

Solubility in water

Chemical reactivity

How does surface area influence powder properties?

It primarily determines the color of the powder.

It only influences the bulk density.

It affects the rate of solution and oxidation. (correct)

It has no significant impact.

Which factor is critical in the stability of colloids?

Concentration of dissolved gases

Presence of lyophilic colloids (correct)

Molecular weight of the solvent

Temperature conditions only

What indicates a successful membrane filtration for sterility?

Pore size decreases to 450 nm Signup and view all the answers

What factor primarily influences the stability of emulsions?

The HLB number of the emulsifying agents Signup and view all the answers

What is the primary distinction between adsorption and absorption?

Adsorption involves accumulation at the interface, while absorption is the penetration into a substance. Signup and view all the answers

Which of the following substances is categorized as an adsorbent?

Activated charcoal Signup and view all the answers

What type of adsorption is characterized by weak van der Waals forces?

Physical adsorption Signup and view all the answers

What effect does an increase in temperature generally have on physical adsorption?

It decreases adsorption capacity. Signup and view all the answers

How does pressure affect adsorption in physical versus chemical adsorption?

Pressure has no effect on physical adsorption. Signup and view all the answers

What is the typical heat of adsorption range for chemical adsorption?

20-100 Kcal/mol Signup and view all the answers

Which of the following is a characteristic of chemical adsorption?

It involves ion exchange processes. Signup and view all the answers

Which statement is true regarding the nature of gas in physical adsorption?

Easily liquefiable gases are adsorbed readily. Signup and view all the answers

What defines positive adsorption?

Surface concentration is greater than volume concentration. Signup and view all the answers

Which factors primarily influence the adsorption process?

Concentration, surface area, and temperature. Signup and view all the answers

What is an example of a substance that showcases negative adsorption?

Strychnine HCl with lower surface concentration. Signup and view all the answers

Which statement accurately describes chemisorption?

It may involve cation exchange mechanisms. Signup and view all the answers

How does temperature affect the adsorption process?

Increased temperature decreases adsorption. Signup and view all the answers

What empirical rule indicates the relationship between solubility and adsorption?

Highly soluble substances have poor or less adsorption. Signup and view all the answers

Which of the following best describes 'sorption'?

A mixture of adsorption and absorption. Signup and view all the answers

What is the primary characteristic of Type I adsorption isotherms?

Dependent on micropore volume. Signup and view all the answers

Which adsorbent is primarily used in respiratory systems?

Activated charcoal. Signup and view all the answers

In what condition is adsorption maximized for single molecule drugs?

When ionization is suppressed. Signup and view all the answers

Which factor increases the adsorption capacity of an adsorbent?

Converting adsorbent to activated form. Signup and view all the answers

What does the heat of adsorption measure?

The energy released when 1gm mole of a gas is adsorbed. Signup and view all the answers

How does pressure influence adsorption?

Higher pressure increases adsorption. Signup and view all the answers

What characterizes the Type II isotherm in adsorption?

It indicates that multilayer adsorption begins after monolayer coverage is complete. Signup and view all the answers

Which type of isotherm is convex to the x-axis and indicates strong lateral interactions among adsorbed molecules?

Type III Signup and view all the answers

What is a key feature of Type IV isotherms?

They have a hysteresis loop due to capillary condensation. Signup and view all the answers

How does Type V isotherm differ from Type IV?

It attributes the initial part to multilayer adsorption but closely follows Type II. Signup and view all the answers

In the BET equation, what does the variable 'nm' represent?

The monolayer capacity. Signup and view all the answers

Which adsorbent type is typically hydrophobic and non-polar?

Activated carbon Signup and view all the answers

What is the pore size range for mesoporous adsorbents?

20 Aº to 500 Aº Signup and view all the answers

Which is NOT a commercial application of activated carbon?

Treatment of edible oils Signup and view all the answers

In which medical application is activated charcoal used?

To remove toxic elements from blood. Signup and view all the answers

What does the process of decolourization involve?

Removing colors using activated charcoal during purification. Signup and view all the answers

What is one main characteristic of microporous adsorbents?

Pore size range of 2 Aº to 20 Aº Signup and view all the answers

Why is activated carbon preferred for the recovery of organic solvents?

It has extensive surface area and porosity. Signup and view all the answers

What does the term 'haemoperfusion' refer to?

A process to filter blood through an adsorbent material. Signup and view all the answers

Which property is NOT associated with activated alumina?

Adsorption of organic pigments. Signup and view all the answers

Study Notes

Adsorption and Absorption

Adsorption is the accumulation of a substance at the interface between two phases, such as gas-solid, gas-liquid, or solid-liquid. It is a surface phenomenon where a substance (adsorbate) concentrates at the surface of another substance (adsorbent).
Absorption is the penetration of one component throughout the body of another. The distinction between adsorption and absorption is not always clear. When both processes occur simultaneously, it's called sorption.

Components of Adsorption

Adsorbent: The substance that adsorbs the other substance. Examples include activated charcoal, kaolin, pectin, and others.
Adsorbate: The substance that is adsorbed onto the adsorbent. Examples include toxins, drugs, and other substances.

Types of Adsorption

Physical Adsorption (Van der Waals): Involves weak van der Waals forces between adsorbent and adsorbate. Easily liquefiable gases are readily adsorbed. The heat of adsorption is small (about 5 kcal/mol). Reversible. Rapid at low temperatures; decreases with increasing temperature. No activation energy involved. Increased pressure leads to increased adsorption; decreased pressure causes desorption. Forms multimolecular layers.
Chemical Adsorption (Chemisorption or Chemical Adsorption): Involves stronger valence forces, often an ion exchange process. More specific than physical adsorption. Heat of adsorption is large (20-100 kcal/mol). Irreversible. Increased with increase of temperature. May involve activation energy. Change of pressure has no such effects. Forms unimolecular layer. Frequently, both physical and chemical adsorption are involved.

Factors Affecting Adsorption

Solubility of Adsorbate: Highly soluble substances adsorb less. (Lundelius' Rule)
Nature of Adsorbate and Adsorbent: Nature of substance affects adsorption. Finely divided adsorbents have higher capacity.
Surface Area: Increased surface area leads to greater adsorption.
Affinity: Stronger affinity between adsorbent and adsorbate results in more adsorption.
Concentration: Greater concentration of adsorbate or adsorbent increases adsorption.
Pressure: Increased pressure leads to increased adsorption.
Temperature: Adsorption is generally an exothermic process. Higher temperature usually leads to decreased adsorption.
pH: Ionization affects solubility, which influences drug adsorption. Maximum at isoelectric point. For single molecules, adsorption increases with decreasing ionization.

Adsorption Isotherms

Adsorption isotherms relate the amount of gas adsorbed to its partial pressure. Type I, II, III, IV, V, and VI isotherms describe different adsorption behaviors, with Type I showing monolayer adsorption on microporous solids, and Type II representing unrestricted monolayer and multilayer adsorption on non-porous solids. Type IV isotherms are common on mesoporous solids and include hysteresis loops. BET equation is used to calculate adsorbed amount on Type I and Type II isotherms.

Types of Adsorbents

Oxygen-containing: Hydrophilic and polar (e.g., silica gel, zeolites).
Carbon-based: Hydrophobic and non-polar (e.g., activated carbon, graphite).
Polymer-based: Polar or non-polar functional groups (e.g., polymers, resins).

Classification of Adsorbents by Pore Size (micropores, mesopores, macropores)

Commercial Adsorbents (examples)

Silica gel
Activated alumina
Activated carbon
Polymers and resins
Clay
Zeolites

Applications of Adsorption

Chromatography (preparative and analytical)
Heterogeneous catalysis
Water purification
Solvent recovery
Medical/Pharmaceutical:
- Removing toxins from the digestive tract
- Removing toxic elements from blood
- Treating drug overdoses (e.g., haemoperfusion).
- Drug formulations: Problems with adsorbents and non-specific nutrients.
Other Applications: Decolourisation, drying, removing pyrogens, determining surface areas, controlling colloidal stability, and emulsion stability and Rheological properties of suspensions

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Description

Test your understanding of adsorption and absorption processes in chemistry. This quiz covers definitions, components, and types of adsorption, including physical adsorption and its characteristics. Challenge yourself with questions that explore these essential concepts!