35 Questions
What type of gels are rigid and do not have the property of elasticity?
Non-elastic gels
What is the process of causing artificial rain by throwing the electrified sand or silver iodide from an aeroplane?
Cloud seeding
What is the theory that proposes the formation of multimolecular layers of gas molecules on the surface of solids?
B.E.T. theory
What is the application of colloids in the purification of water?
Coagulation
What type of catalysts are Bronsted acids and bases?
Acid-base catalysts
What is the purpose of adding Al³⁺ ions to water in the purification process?
To remove negatively charged clay particles
What is the study of the nature of surfaces and chemical and physical processes that take place on surfaces called?
Surface chemistry
What is the phenomenon of attracting and retaining molecules of a substance on the surface of a liquid or solid resulting in higher concentration of molecules on the surface called?
Adsorption
What is the term for the substance that gets adsorbed on any surface?
Adsorbate
What is the main cause of adsorption?
Unbalanced forces of attraction or free valencies on the surface
What is an example of adsorption?
Ammonia gas in contact with charcoal
What is the branch of physical chemistry that deals with the nature of surfaces and the chemical and physical processes that take place on surfaces?
Surface chemistry
What is the primary function of soap and detergents in cleaning?
To reduce the surface tension between dirt and cloth
What is the purpose of the froth floatation process?
To separate low-grade sulphide ore from silica and other earthy matter
What is the property of certain precipitates, such as silver halide, that allows them to be used in adsorption indicators?
They are able to adsorb some dyes
What is the term for the catalytic process in which the reactants and the catalyst are in different phases?
Heterogeneous catalysis
What is an example of heterogeneous catalysis?
Hydrolysis of NO2 to form NO
What is the purpose of chromatographic analysis?
To separate and identify the components of a mixture
What is the limitation of the Freundlich adsorption isotherm?
It fails at high pressure of the gas
What is the form of the solute in a solution that can undergo adsorption?
Either molecular or ionic form
What is the name of the adsorption isotherm derived by Irving Langmuir in 1916?
Langmuir adsorption isotherm
What is the purpose of adding Al³⁺ ions to water in the purification process?
To cause coagulation of colloidal particles
What is the process of causing artificial rain by throwing electrified sand or silver iodide from an aeroplane?
Cloud seeding
What is the primary reason for the increased adsorption tendency of a substance when its surface area is increased?
Unbalanced forces on the surface atoms
In which type of adsorption is the concentration of the adsorbed molecules always greater at the surface than in the bulk phase?
Positive adsorption
What is the primary function of adding alum (Al³⁺ ions) to water in the purification process?
Coagulation of colloidal particles
What is the purpose of throwing electrified sand or silver iodide from an aeroplane to induce artificial rain?
To induce coagulation of water droplets
What is the term for the graph that represents the amount of adsorbate adsorbed per unit mass of adsorbent at different pressures and temperatures?
Adsorption isotherm
What is the primary mechanism behind the purification of water using adsorption?
Adsorption of impurities on the surface of the adsorbent
What does the Freundlich adsorption isotherm equation indicate about the amount of gas adsorbed?
It does not increase as rapidly as the pressure
Under what conditions is Langmuir's theory of unimolecular adsorption valid?
At low pressures and high temperatures
What happens to the extent of adsorption at high pressure according to the Freundlich adsorption isotherm?
It becomes independent of pressure
What is the relationship between the amount of gas adsorbed and pressure at low pressure according to the Freundlich adsorption isotherm?
The amount of gas adsorbed varies linearly with pressure
What is the significance of the exponent n in the Freundlich adsorption isotherm equation?
It is always greater than one
What is the physical significance of the slope of the plot of x/m against p in the Freundlich adsorption isotherm?
It represents the reciprocal of the exponent n
Study Notes
Types of Gels
- Elastic gels: change shape when force is applied and return to original shape when force is removed (e.g. gelatin, agar-agar, starch)
- Non-elastic gels: rigid and do not have elasticity (e.g. silica gel)
Surface Chemistry
- Definition: branch of physical chemistry that deals with the nature of surfaces and chemical and physical processes that take place on surfaces
- Studies phenomenon of adsorption, catalysis, and colloidal properties
Adsorption
- Definition: phenomenon of attracting and retaining molecules of a substance on the surface of a liquid or solid, resulting in higher concentration of molecules on the surface
- Causes of adsorption: unbalanced forces of attraction or free valencies present at the solid or liquid surface
- Example: ammonia gas adsorbed on charcoal
Adsorption Isotherms
- Freundlich adsorption isotherm: describes adsorption where adsorbate forms a monomolecular layer on the surface of the adsorbent
- Equation: x/m = kp^(1/n)
- Characteristics: x/m increases with p at low pressure, becomes independent of p at high pressure, and depends on p^(1/n) at moderate pressure
- Langmuir adsorption isotherm: describes adsorption at low pressures and high temperatures, fails at high pressures and low temperatures
- Limitation: fails to describe multilayer adsorption
Classification of Adsorption
- Positive adsorption: concentration of adsorbate is more on the surface than in the bulk phase
- Example: adsorption of water vapors by anhydrous CaCl2
- Surface forces: unbalanced forces of attraction or free valencies present at the solid or liquid surface
- Examples: Vander Waal's forces, chemical bond forces
Applications of Colloids
- Purification of water: coagulation using alum
- Artificial rains: throwing electrified sand or silver iodide from an airplane to coagulate mist
- Cleaning agents: soap and detergents adsorb on the interface, reducing surface tension between dirt and cloth
- Froth floatation process: separating low-grade sulphide ore from silica and other earthy matter
- Adsorption indicators: surface of certain precipitates adsorbs dyes
- Chromatographic analysis: separating and analyzing mixtures
Catalysis
- Heterogeneous catalysis: catalytic process in which reactants and catalyst are in different phases
- Examples: surface chemistry, adsorption, and catalysis of chemical reactions
Test your knowledge of surface chemistry, including the concept of interfaces, phases, and adsorption. Learn about the branch of physical chemistry that deals with the nature of surfaces and the processes that occur on them.
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