Chemistry MCQs
Topic Notes: Chemistry
MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
1
Which laboratory or industrial method is utilized to separate cream from milk?
Answer:
Centrifugation
Centrifugation is the standard method for separating cream from milk. By spinning the milk at high speeds, the denser components (skim milk) are forced outward toward the walls of the centrifuge, while the lighter components (cream/fat globules) remain closer to the center, allowing for efficient separation.
2
What is the fundamental physical principle by which detergents facilitate the cleaning of surfaces?
Answer:
surface tension
Detergents are surfactants that function by lowering the surface tension of water. This reduction allows the water to penetrate fabrics more effectively and emulsify oils and grease, lifting dirt particles from the surface so they can be washed away.
3
Which of the following phenomena is not a direct result of surface tension?
Answer:
Vapour formation above the liquid surface
Surface tension is a property resulting from cohesive forces between molecules at the surface of a liquid. While it explains capillary action, meniscus shape, and the tendency of droplets to become spherical to minimize surface area, vapor formation is a result of kinetic energy and evaporation, not surface tension.
4
Which salt is the most predominant component found in ocean water?
Answer:
Sodium Chloride
Sodium chloride (NaCl), commonly known as table salt, is the most abundant dissolved salt in the Earth's oceans. It accounts for the majority of the salinity of seawater, significantly outweighing other dissolved minerals like magnesium sulfate or calcium carbonate.
5
Which of the following substances exhibits the highest viscosity?
Answer:
Honey
Viscosity is a measure of a fluid's resistance to flow. Among the options provided, honey has a much higher internal friction and resistance to flow compared to water, alcohol, or gasoline, which are relatively thin and flow easily.
6
How is milk classified in terms of colloidal systems?
Answer:
emulsion
Milk is classified as an emulsion, which is a type of colloid where two immiscible liquids are dispersed within one another. Specifically, it consists of tiny globules of butterfat (the dispersed phase) suspended in an aqueous solution (the continuous phase), stabilized by proteins like casein.
7
How is soil classified in terms of mixture types?
Answer:
Heterogeneous mixture
Soil is a heterogeneous mixture because its composition is not uniform. It consists of various components such as sand, clay, organic matter, minerals, and water, which are distributed unevenly throughout the sample, allowing for distinct phases to be identified.
8
Which physical property of water is primarily responsible for its high effectiveness as a universal solvent?
Answer:
dielectric constant of water
Water is an excellent solvent because of its high dielectric constant. This property allows water to effectively reduce the electrostatic forces of attraction between ions in an ionic crystal lattice, facilitating the dissociation of ionic compounds into their constituent ions in an aqueous solution.
9
Which of the following substances is not classified as a colloid?
Answer:
Honey
A colloid is a mixture where microscopically dispersed insoluble particles are suspended throughout another substance. Milk, blood, and ice-cream are classic examples of colloidal systems (emulsions or sols). Honey, however, is primarily a supersaturated solution of sugars (glucose and fructose) in water, making it a true solution rather than a colloid.
10
How is an emulsion defined in terms of its colloidal components?
Answer:
liquid in a liquid
An emulsion is a specific type of colloid consisting of two immiscible liquids where one liquid is dispersed as fine droplets within the other. Common examples include milk (fat in water) and mayonnaise. The stability of an emulsion is often maintained by an emulsifying agent that prevents the droplets from coalescing back into separate layers.