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Question 1:
How does the rate of evaporation respond to an increase in temperature?
Topic: Evaporation and Temperature correlation
Correct Answer: A) It increases
Detailed Hint:
- Evaporation is a process influenced by temperature. When temperature rises, the kinetic energy of the molecules also escalates.
- This increase in kinetic energy implies that the molecules move more rapidly, allowing them to escape the surface and transform into a gas, which is the essence of evaporation.
- Consequently, an increase in temperature correlates with a surge in the rate of evaporation. Thus the right answer is A, "It increases".
Question 2:
Which of the following exhibits the strongest London dispersion forces?
Topic: London Dispersion Forces
Correct Answer: D) I2
Detailed Hint:
- London dispersion forces (LDF) are temporary attractive forces that result when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles.
- Among the list, I2 has the most significant London dispersion forces because of its larger size and consequently, its greater polarizability.
- The larger the molecule, the more easily it is polarized, leading to stronger LDF. Hence, the right answer is D, "I2".
Question 3:
Which state of matter predominates the universe?
Topic: States of Matter in the Universe
Correct Answer: D) Plasma
Detailed Hint:
- Among the four fundamental states of matter - solid, liquid, gas, and plasma, plasma is the most abundant in the universe.
- Plasma makes up 99 percent of the visible universe and is composed of charged particles: positive ions and negative electrons.
- Therefore, the correct answer is D, "Plasma".
Question 4:
Why is Kerosene a liquid at room temperature?
Topic: Physical State and Molecular Characteristics
Correct Answer: D) Molecular size
Detailed Hint:
- The physical state of a substance at room temperature is determined by the type and strength of the intermolecular forces acting between the particles of the substance.
- In the case of kerosene, its liquid state at room temperature is primarily due to the size of its molecules. The larger the molecule, the greater its polarizability and the stronger the attractive forces between its particles.
- Hence, the appropriate answer is D, "Molecular size".
Question 5:
Why do higher alkanes have a greater boiling point than lower alkanes?
Topic: Boiling Point and Molecular Structure
Correct Answer: B) Higher alkanes are more polarizable
Detailed Hint:
- The boiling point of a substance is related to the strength of the intermolecular forces it experiences. Higher intermolecular forces result in a higher boiling point.
- For alkanes, these forces are primarily London dispersion forces, which increase with the size and complexity of the molecule.
- Higher alkanes have larger, more complex structures, leading to increased polarization and a higher boiling point. Therefore, the correct answer is B, "Higher alkanes are more polarizable".
Question 6:
What is the most effective method to test the purity of a suspected sample of Ethanoic acid (acetic acid)?
Topic: Testing Purity of a Substance
Correct Answer: A) Measure its boiling point
Detailed Hint:
- The purity of a substance can often be determined by its physical properties. One such property is the boiling point.
- A pure substance will boil at a specific, constant temperature under a given set of conditions.
- For Ethanoic acid (acetic acid), this means testing its boiling point would be the most effective way to determine its purity. Hence, the right answer is A, "Measure its boiling point".
Question 7:
What is the term for the maximum temperature at which a substance can exist as a liquid?
Topic: States of Matter and Temperature
Correct Answer: D) Critical temperature
Detailed Hint:
- The state of a substance, solid, liquid, or gas, is dependent on temperature and pressure.
- A substance can exist as a liquid up to a certain maximum temperature, beyond which it will become a gas regardless of the pressure.
- This maximum temperature is known as the critical temperature. Therefore, the correct answer is D, "Critical temperature".
Question 8:
At what point does a liquid reach its boiling point?
Topic: Boiling Point and Vapor Pressure
Correct Answer: D) When its vapor pressure equals 760 torr at sea level
Detailed Hint:
- The boiling point of a liquid is the temperature at which its vapor pressure equals the pressure surrounding the liquid.
- As the temperature of a liquid increases, its vapor pressure rises until it equals the atmospheric pressure.
- This condition indicates that the liquid is boiling. Hence, under normal conditions at sea level (1 atmospheric pressure), the vapor pressure needed to reach boiling point is 760 torr.
Question 9:
What change does not occur when a substance transitions from a solid to a liquid state?
Topic: Phase Transitions and Molecular Behavior
Correct Answer: B) The kinetic energy of the molecules decreases
Detailed Hint:
- The transition from a solid to a liquid state involves a change in molecular organization and energy.
- The molecules become more disordered and separated due to increased kinetic energy.
- Thus, it's incorrect to say that the kinetic energy decreases during this phase transition. The correct answer is B.
Question 10:
Which liquid has the highest vapor pressure?
Topic: Vapor Pressure and Molecular Interactions
Correct Answer: C) Ether
Detailed Hint:
- Vapor pressure is a measure of a substance's tendency to evaporate, and it increases with weaker intermolecular forces.
- Ethers are known for their volatility due to relatively weak intermolecular forces.
- Therefore, of the options given, Ether (C) would have the highest vapor pressure.
Question 11:
Which process leads to a reduction in the strength of attractions between particles?
Topic: Phase Changes and Particle Interactions
Correct Answer: D) Evaporation
Detailed Hint:
- The process of evaporation involves a transition of matter from a liquid state to a gaseous state.
- During this process, the intermolecular forces of attraction among the liquid particles are weakened, allowing them to escape as gas.
- In contrast, freezing, condensation, and crystallization involve a shift to a state where intermolecular forces are stronger.
- Thus, the only process that weakens the attraction among particles is evaporation.
Question 12:
For which type of molecules are London dispersion forces particularly significant?
Topic: Intermolecular Forces and Molecular Polarity
Correct Answer: D) Non-polar molecules
Detailed Hint:
- London dispersion forces are temporary attractive forces that occur due to the momentary changes in electron distribution in atoms and molecules.
- They are present in all types of molecules, but they are especially significant for non-polar molecules.
- Non-polar molecules like CH4, CCl4, Cl2, H2, and noble gases rely mainly on London dispersion forces for intermolecular interactions.
- Hence, option D is the correct answer.
Question 13:
Which statement is incorrect regarding the process of evaporation?
Topic: Evaporation and Energy Changes
Correct Answer: C) It is an exothermic process
Detailed Hint:
- Evaporation is a process in which liquid changes into gas at a temperature below its boiling point.
- It occurs on the surface of the liquid and is a continuous process that leads to cooling.
- However, evaporation is not an exothermic process, which involves the release of heat.
- Instead, it is an endothermic process that absorbs heat from its surroundings.
- Therefore, statement C is incorrect, making it the correct answer.
Question 14:
What factors influence the vapor pressure of a liquid?
Topic: Vapor Pressure and its Determinants
Correct Answer: D) All of these
Detailed Hint:
- Vapor pressure refers to the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases at a given temperature.
- Various factors can affect this equilibrium, including the size of the molecules, temperature, and intermolecular forces.
- Larger molecules tend to have higher vapor pressures due to increased intermolecular forces.
- Temperature also plays a key role, with higher temperatures leading to increased vapor pressures.
- Intermolecular forces can affect how easily molecules escape from the liquid phase to the vapor phase, thus affecting vapor pressure.
- Therefore, all these factors (option D) contribute to the vapor pressure of a liquid.
MCQs 15:
What are the boiling points of H2O and C2H5OH?
Topic: Boiling Points and Molecular Interactions
Correct Answer: B) Different
Detailed Hint:
- The boiling point of a substance is the temperature at which it changes from a liquid to a gas under a given pressure.
- For water (H2O), the boiling point is 100°C at 760 torr.
- On the other hand, ethanol (C2H5OH) has a boiling point of 78.5°C at the same pressure.
- This discrepancy arises from the differing intermolecular forces present in each substance.
- Hence, the boiling points of H2O and C2H5OH are different (option B).
MCQs 16:
What happens to the strength of London dispersion forces as the size of molecules increase?
Topic: London Dispersion Forces and Molecular Size
Correct Answer: A) Increase
Detailed Hint:
- London dispersion forces are temporary, weak attractive forces that occur due to momentary changes in electron distribution in atoms and molecules.
- These forces are present in all types of molecules, but they become more substantial as the size of the molecules increases.
- Larger molecules have more electrons, which create stronger temporary dipoles and intermolecular attractions.
- Therefore, as the size of molecules increases, the strength of London dispersion forces also increases (option A).
MCQs 17:
Which substance has the highest boiling point?
Topic: Boiling Points and Hydrogen Bonding Strength
Correct Answer: D) (CH2)2-(OH)2
Detailed Hint:
- The boiling point of a molecule often depends on the type and strength of the intermolecular forces acting within it.
- Hydrogen bonds, a specific type of dipole-dipole interaction, are especially strong intermolecular forces.
- More hydrogen bonds in a molecule usually equate to a higher boiling point due to an increase in the strength of these forces.
- H2O has one OH group implying a single hydrogen bond, while (CH2)2-(OH)2 has two OH groups implying more hydrogen bonds.
- Therefore, (CH2)2-(OH)2 (option D) has a higher boiling point.
MCQs 18:
In which of the following is hydrogen bonding not present?
Topic: Presence of Hydrogen Bonding in Substances
Correct Answer: B) Ether
Detailed Hint:
- Hydrogen bonding is a strong type of dipole-dipole intermolecular force that occurs when a hydrogen atom is bonded to a highly electronegative atom.
- Water, ethanol, and ammonia all have hydrogen atoms bonded to oxygen or nitrogen, which are highly electronegative and thus can form hydrogen bonds.
- Ether, represented as R–O–R, lacks the necessary hydrogen atom bonded to an electronegative element to form hydrogen bonds.
- Hence, hydrogen bonding is not present in Ether (option B).
MCQs 19:
What is the SI unit of surface tension?
Topic: Surface Tension and Units of Measurement
Correct Answer: A) Nm-1
Detailed Hint:
- Surface tension is a property of liquids that results from the cohesive forces between liquid molecules.
- It is defined as the tangential force acting per unit length of a liquid surface.
- Therefore, the SI unit for surface tension is represented as force per unit length which is Newton per meter or N/m.
- Thus, the correct answer is Nm-1 (Option A).
MCQs 20:
What is the external pressure required to raise the boiling point of water to 110°C?
Topic: Boiling Point and External Pressure
Correct Answer: A) Between 760 torr and 1200 torr
Detailed Hint:
- The boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure.
- For water, its boiling point is 100°C at a standard atmospheric pressure of 760 torr.
- If the boiling point of water is to increase, the external pressure must also increase.
- Hence, to achieve a boiling point of 110°C for water, the external pressure would have to be between 760 torr and 1200 torr (option A).
MCQs 21:
Which of the following factors influence the rate of evaporation of liquids?
Topic: Factors Impacting Evaporation Rate
Correct Answer: C) i and ii
Detailed Hint:
- Evaporation is a surface phenomenon where molecules from a liquid state change to a gaseous state.
- The temperature of the liquid influences the kinetic energy of its molecules; hence, an increase in temperature increases the evaporation rate.
- The strength of intermolecular forces also affects evaporation. Stronger forces make it harder for molecules to leave the liquid, thus slowing evaporation.
- Consequently, both temperature and strength of intermolecular forces (Option C) affect the evaporation rate.
Question 22:
In which of the following molecules are London dispersion forces the dominant intermolecular force?
Topic: Dominant Intermolecular Forces
Correct Answer: D) CCl4
Detailed Hint:
- London dispersion forces are the weakest intermolecular forces and act between all atoms and molecules.
- These forces become dominant in molecules that lack stronger intermolecular forces, such as dipole-dipole interactions or hydrogen bonding.
- CCl4 is a nonpolar molecule; hence, it lacks dipole-dipole interactions.
- As a result, the major intermolecular forces present in CCl4 are London dispersion forces (option D).
Question 23:
Which of the following factors does not have an impact on the vapor pressure of a liquid?
Topic: Factors Impacting Vapour Pressure
Correct Answer: C) Surface area
Detailed Hint:
- Vapour pressure is an intrinsic property of a substance, which is dependent on the nature of the substance itself, not the amount of it present.
- The temperature affects the kinetic energy of the molecules, thereby influencing the vapour pressure.
- Intermolecular forces also determine vapour pressure; stronger forces make it harder for molecules to escape the liquid and become vapor.
- The surface area, unlike the other options, does not affect the vapour pressure (Option C).
Question 24:
What is the reason behind the escalating vapor pressure when a liquid is heated?
Topic: Heat and Vapour Pressure
Correct Answer: C) Increase in kinetic energy of molecules
Detailed Hint:
- When a liquid is heated, the kinetic energy of its molecules increases as they move more rapidly.
- This increased motion translates to a greater number of molecules achieving the energy necessary to transition into the gaseous phase, thereby escalating the vapor pressure.
- Therefore, the increase in vapor pressure upon heating a liquid is primarily due to the increased kinetic energy of the molecules (option C).
Question 25:
Identify the weakest intermolecular force from the options below:
Topic: Strength of Intermolecular Forces
Correct Answer: D) London dispersion forces
Detailed Hint:
- Intermolecular forces are the forces of attraction between molecules. They are weaker than the intramolecular forces within a molecule but crucial for determining properties of substances.
- Dipole-dipole, ion-dipole, and dipole-induced dipole forces are all relatively stronger than London dispersion forces.
- London dispersion forces are the weakest intermolecular forces and occur in all substances, regardless of polarity (option D).
Question 26:
Why does C2H5OH (Ethanol) dissolve in water?
Topic: Solubility and Hydrogen Bonding
Correct Answer: B) It can form hydrogen bonding with water
Detailed Hint:
- Ethanol (C2H5OH) is a type of alcohol that is capable of dissolving in water.
- As a hydrocarbon, ethanol does have non-polar characteristics, but this is not the primary reason for its solubility in water.
- The main factor for its solubility is its ability to form hydrogen bonds with water (Option B), due to the presence of a polar OH (hydroxyl) group in its structure.
- The solubility coefficient is not the key factor for its solubility in water.
Question 27:
What is the reason for the decrease in density of water when it freezes at 0°C?
Topic: Density and Phases of Water
Correct Answer: B) Empty spaces present in the structure of ice
Detailed Hint:
- When water freezes into ice at 0°C, its density decreases.
- This is not primarily due to the cubic structure of ice, changes in bond lengths, or bond angles.
- Instead, the decrease in density is primarily because of the formation of a more regular structure in ice that creates empty spaces (Option B).
- These empty spaces cause ice to occupy more volume than water, thus reducing its density.
Question 28:
What is the term for the amount of heat absorbed when one mole of a solid melts into a liquid at its melting point?
Topic: Phase Change and Heat Transfer
Correct Answer: D) Molar heat of fusion
Detailed Hint:
- The process of converting a solid into a liquid involves the absorption of heat.
- This heat is not related to sublimation (directly converting a solid into a gas) or vaporization (converting a liquid into a gas).
- The heat absorbed during this process is typically referred to as the latent heat of fusion, but when it is associated with one mole of a substance, the term used is the molar heat of fusion (Option D).
- This term represents the amount of heat energy required to melt one mole of a solid at its melting point.
MCQs 29:
What is the correct sequence of boiling points for the following liquids: H2O, HF, HCl, NH3?
Topic: Intermolecular Forces and Boiling Point
Correct Answer: D) H2O > HF > NH3 > HCl
Detailed Hint:
- The boiling point of a liquid is directly related to the strength of its intermolecular forces; stronger forces result in higher boiling points.
- Water (H2O) has strong hydrogen bonding which makes it have the highest boiling point among the given substances.
- HF also has hydrogen bonding, but it is weaker than that in H2O.
- NH3, like H2O and HF, forms hydrogen bonds but these are weaker still, resulting in a lower boiling point.
- HCl, on the other hand, primarily experiences dipole-dipole interactions, which are weaker than hydrogen bonds, giving it the lowest boiling point (Option D).
MCQs 30:
Under what external pressure could water boil at 120°C?
Topic: Vapor Pressure and Boiling Point
Correct Answer: D) 1489 mm Hg
Detailed Hint:
- The boiling point of a liquid is the temperature at which its vapor pressure equals the external pressure.
- Normally, water boils at 100°C under 1 atmosphere pressure which is approximately 760 mm Hg.
- When the boiling point is higher (like 120°C in this case), it means the external pressure must also be higher.
- Thus, to have water boil at 120°C, the external pressure must be greater, like 1489 mm Hg (Option D).