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
31
Which of the following substances is considered an effective desiccant?
Answer:
Silica gel
A desiccant is a hygroscopic substance used to induce or sustain a state of dryness in its vicinity. Silica gel is a highly porous form of silicon dioxide that has a large surface area, allowing it to adsorb water molecules effectively from the air, making it a standard industrial and laboratory desiccant.
32
What is the term for the mass of water vapor present per unit volume of air?
Answer:
absolute humidity
Absolute humidity is defined as the total mass of water vapor present in a given volume of air, typically expressed in grams per cubic meter (g/m³). It is independent of temperature, unlike relative humidity, which is a ratio of the actual vapor pressure to the saturation vapor pressure at a specific temperature.
33
Identify which of the following properties are classified as transport properties: 1. Viscosity, 2. Surface tension, 3. Thermal conductance, 4. Diffusion.
Answer:
1, 3, 4
Transport properties describe the rate at which physical quantities are transported through a system. Viscosity (momentum transport), thermal conductance (energy transport), and diffusion (mass transport) are classic transport properties. Surface tension is a thermodynamic property related to surface energy, not a transport property.
34
Which of the following substances is classified as a pure substance rather than a mixture?
Answer:
Ice
Ice is the solid state of water (H2O), which is a chemical compound consisting of fixed proportions of hydrogen and oxygen. In contrast, air, ice-cream, and honey are mixtures containing various components that do not have a fixed chemical formula or constant composition throughout.
35
Which process is commonly employed to purify seawater into potable water?
Answer:
distillation
Distillation is the most effective method for purifying seawater because it involves boiling the water to create steam, which is then condensed back into liquid form, leaving behind dissolved salts and impurities. This process ensures the removal of non-volatile solutes, providing high-purity water suitable for consumption.
36
In which of the following solvents is magnesium chloride (MgCl2) most likely to be soluble?
Answer:
Water
Magnesium chloride is an ionic compound. According to the principle of 'like dissolves like', ionic compounds are highly soluble in polar solvents like water due to ion-dipole interactions. It is generally insoluble in non-polar organic solvents like kerosene or petrol.
37
What physical principle is responsible for the separation of cream from milk during vigorous churning?
Answer:
centrifugal force
Churning milk involves rapid rotation, which creates a centrifugal force. This force acts on the components of the milk based on their density. The lighter fat globules (cream) are pushed toward the center or separated from the denser skim milk, allowing for their collection.
38
Why does a soap solution used for cleaning appear cloudy?
Answer:
scatter light
Soap solutions appear cloudy because they form colloidal systems known as micelles. These micelles are large enough to interact with visible light, causing the Tyndall effect, where the particles scatter the light in different directions, resulting in a cloudy or opalescent appearance.
39
Which term describes a homogeneous mixture consisting of two or more chemical components?
Answer:
Solutions
A solution is defined as a homogeneous mixture of two or more substances at the molecular or ionic level. The components are uniformly distributed throughout the mixture, resulting in a single phase.
40
What is the physical nature of a cloud in terms of colloidal dispersion?
Answer:
water drops in a dispersion medium of air
A cloud is a colloidal system known as an aerosol. In this system, liquid water droplets (the dispersed phase) are suspended in a gas, specifically air (the dispersion medium). This classification distinguishes it from other colloids like foams or gels.