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Chemistry Test - 30

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Chemistry Test - 30
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  • Question 1
    5 / -1

    Read the following passage carefully:

    Catalysts are the chemical substances used in chemical reactions to accelerate the rate of reaction. Different reactions can be accelerated using different catalysts. Catalysts themselves do not get consumed in the reaction. In biological systems, enzyme serves the function of catalyst for different metabolic processes.

    Which of the following statement is true regarding enzymes?

    Solution

    Enzymes are biological catalysts that accelerate biochemical reactions by lowering activation energy.

    • Option A: False. Only specific enzymes (e.g., multi-site enzymes) can bind multiple substrate molecules simultaneously, but this is not a general property of all enzymes.
    • Option B: True. Many vital biochemical reactions (e.g., metabolic processes) can occur without enzymes, but at a much slower rate, as enzymes enhance reaction efficiency.
    • Option C: False. Enzymes are highly sensitive to pH and temperature, denaturing outside their optimal ranges.
    • Option D: False. Enzymes are typically specific, catalyzing one or a few related reactions, not numerous unrelated roles.
  • Question 2
    5 / -1

    Which one of the following statement is NOT correct for detergents?

    Solution

    Detergents are cleaning agents, including soaps and synthetic detergents. Unlike soaps:

    • Option A: True. Synthetic detergents have properties similar to soaps (cleaning ability).
    • Option B: True. Synthetic detergents can be used in both soft and hard water, forming foam even in hard water.
    • Option C: False. Synthetic detergents can be used in acidic media, unlike soaps, which precipitate.
    • Option D: True. Synthetic detergents are often derived from vegetable oils or petrochemicals.

    Thus, the correct answer is C.

  • Question 3
    5 / -1

    The incorrect statement among the following is:

    Solution
    • Option A: True. Actinoids are highly reactive, especially when finely divided, due to their metallic nature.
    • Option B: True. Actinoid contraction is greater than lanthanoid contraction because 5f electrons have poorer shielding than 4f electrons, leading to a stronger nuclear pull.
    • Option C: False. Most trivalent lanthanoid ions (e.g., La³⁺, Ce³⁺, Gd³⁺, Lu³⁺) are colorless in both solid and aqueous states due to the absence of f-f transitions (e.g., f⁰, f⁷, f¹⁴ configurations). Only some lanthanoids with partially filled f-orbitals (e.g., Nd³⁺, Er³⁺) show color.
    • Option D: True. Lanthanoids have metallic structures, making them good conductors of heat and electricity.

    Thus, the correct answer is C.

  • Question 4
    5 / -1

    Which statement(s) stands true for Langmuir isotherm?

    (a) Adsorption can be monolayer or multilayer.

    (b) The probability of adsorption is independent of the occupation of neighbouring sites i.e. there is no interaction between adsorbed molecules.

    Solution

    The Langmuir isotherm describes adsorption with the following assumptions:

    • Adsorption occurs in a single (monolayer) layer on a homogeneous surface.
    • There is no interaction between adsorbed molecules, so the probability of adsorption at a site is independent of neighboring sites.
    • A dynamic equilibrium exists between adsorption and desorption.
    • Statement (a): False. The Langmuir isotherm assumes only monolayer adsorption, not multilayer.
    • Statement (b): True. Adsorption probability is independent of neighboring site occupancy.

    Thus, the correct answer is A: Only (b) is true.

  • Question 5
    5 / -1

    Which of the following statement is incorrect about the order of a reaction?

    Solution

    The order of a reaction is defined as the sum of the powers of reactant concentrations in the rate law expression (e.g., for aA + bB → products, rate = k[A]x[B]y, order = x + y).

    • Option A: True. The order is determined experimentally by measuring rate changes with concentration.
    • Option B: True. The order can be zero, integer, or fractional (e.g., in complex reactions).
    • Option C: True. The order applies to both elementary (where it matches stoichiometry) and complex reactions.
    • Option D: False. The order is not always equal to the sum of stoichiometric coefficients, as it depends on the rate-determining step, not the balanced equation.

    Thus, the correct answer is D.

  • Question 6
    5 / -1

    Directions For Questions

    Read the following passage carefully:

    Colligative properties are those properties of a solution that depend on the number of particles of the solute dispersed in the solvent, not on the nature of the chemical species present. These properties provide important insight into understanding the behavior of solutions and have practical applications in various fields, including chemistry and biochemistry. The four main colligative properties are vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. Vapor Pressure Lowering, When a non-volatile solute is dissolved in a solvent, the vapor pressure of the solvent decreases. This is because the solute particles occupy space on the surface of the solution, making fewer solvent molecules available to escape into the vapor phase. Boiling Point Elevation, The addition of a solute to a solvent increases the solution's boiling point. This elevation occurs because the lowered vapor pressure requires a higher temperature to reach the atmospheric pressure, necessitating additional heat. Freezing Point Depression, The presence of a solute also lowers the freezing point of a solvent. This happens as the solute particles interfere with the solvent molecules' ability to form a solid structure, meaning the solution must be cooled to a lower temperature to solidify. Osmotic Pressure, This property refers to the pressure required to stop the solvent's flow across a semipermeable membrane from a dilute solution to a more concentrated one. Osmotic pressure is direct evidence of the presence of solute particles and is proportional to the concentration of the solute.

    ...view full instructions

    Why do colligative properties not significantly change with the addition of a small amount of a weak electrolyte to a solution?

    Solution

    The correct answer is Weak electrolytes do not dissociate completely.

    • Colligative properties depend on the number of solute particles in a solution, not the type of particles. Weak electrolytes, such as acetic acid, do not dissociate completely into ions when dissolved in a solvent.
    • This incomplete dissociation means that the total number of particles added to the solution is relatively low compared to strong electrolytes, which dissociate fully.
    • Therefore, the addition of a small amount of a weak electrolyte has a less significant effect on the solution's colligative properties because it contributes fewer particles to the solution than a strong electrolyte would.

    So, the colligative properties not significantly change with the addition of a small amount of a weak electrolyte to a solution since Weak electrolytes do not dissociate completely.

  • Question 7
    5 / -1

    Directions For Questions

    Read the following passage carefully:

    Colligative properties are those properties of a solution that depend on the number of particles of the solute dispersed in the solvent, not on the nature of the chemical species present. These properties provide important insight into understanding the behavior of solutions and have practical applications in various fields, including chemistry and biochemistry. The four main colligative properties are vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. Vapor Pressure Lowering, When a non-volatile solute is dissolved in a solvent, the vapor pressure of the solvent decreases. This is because the solute particles occupy space on the surface of the solution, making fewer solvent molecules available to escape into the vapor phase. Boiling Point Elevation, The addition of a solute to a solvent increases the solution's boiling point. This elevation occurs because the lowered vapor pressure requires a higher temperature to reach the atmospheric pressure, necessitating additional heat. Freezing Point Depression, The presence of a solute also lowers the freezing point of a solvent. This happens as the solute particles interfere with the solvent molecules' ability to form a solid structure, meaning the solution must be cooled to a lower temperature to solidify. Osmotic Pressure, This property refers to the pressure required to stop the solvent's flow across a semipermeable membrane from a dilute solution to a more concentrated one. Osmotic pressure is direct evidence of the presence of solute particles and is proportional to the concentration of the solute.

    ...view full instructions

    What accurately describes how boiling point elevation and freezing point depression are related to solute concentration?

    Solution

    The correct answer is They are both linearly proportional

    • Both boiling point elevation and freezing point depression are linearly proportional to the molal concentration of the solute in the solution.
    • This relationship is described by formulas (ΔTb=Kb⋅mΔTb=Kb⋅m) for boiling point elevation and (ΔTf=Kf⋅mΔTf=Kf⋅m) for freezing point depression, where (ΔTb) and (ΔTf) are the changes in boiling and freezing points, respectively, (Kb) and (Kf) are the ebullioscopic and cryoscopic constants, and (m) is the molality of the solution.
    • This linear proportionality makes it easier to predict the changes in these properties based on the concentration of the solute.

    So, the correct answer is They are both linearly proportional.

  • Question 8
    5 / -1

    Directions For Questions

    Read the following passage carefully:

    Colligative properties are those properties of a solution that depend on the number of particles of the solute dispersed in the solvent, not on the nature of the chemical species present. These properties provide important insight into understanding the behavior of solutions and have practical applications in various fields, including chemistry and biochemistry. The four main colligative properties are vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. Vapor Pressure Lowering, When a non-volatile solute is dissolved in a solvent, the vapor pressure of the solvent decreases. This is because the solute particles occupy space on the surface of the solution, making fewer solvent molecules available to escape into the vapor phase. Boiling Point Elevation, The addition of a solute to a solvent increases the solution's boiling point. This elevation occurs because the lowered vapor pressure requires a higher temperature to reach the atmospheric pressure, necessitating additional heat. Freezing Point Depression, The presence of a solute also lowers the freezing point of a solvent. This happens as the solute particles interfere with the solvent molecules' ability to form a solid structure, meaning the solution must be cooled to a lower temperature to solidify. Osmotic Pressure, This property refers to the pressure required to stop the solvent's flow across a semipermeable membrane from a dilute solution to a more concentrated one. Osmotic pressure is direct evidence of the presence of solute particles and is proportional to the concentration of the solute.

    ...view full instructions

    In the context of freezing point depression, why do roads get treated with salt in winter?

    Solution

    Freezing point depression is a colligative property where a solute lowers the freezing point of a solvent. Adding salt (e.g., NaCl) to water on roads dissolves into ions, reducing the freezing point of the resulting solution below 0°C. This prevents ice formation, enhancing road safety in winter.

    Correct answer: C: To decrease the freezing point of water.

  • Question 9
    5 / -1

    Directions For Questions

    Read the following passage carefully:

    Colligative properties are those properties of a solution that depend on the number of particles of the solute dispersed in the solvent, not on the nature of the chemical species present. These properties provide important insight into understanding the behavior of solutions and have practical applications in various fields, including chemistry and biochemistry. The four main colligative properties are vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. Vapor Pressure Lowering, When a non-volatile solute is dissolved in a solvent, the vapor pressure of the solvent decreases. This is because the solute particles occupy space on the surface of the solution, making fewer solvent molecules available to escape into the vapor phase. Boiling Point Elevation, The addition of a solute to a solvent increases the solution's boiling point. This elevation occurs because the lowered vapor pressure requires a higher temperature to reach the atmospheric pressure, necessitating additional heat. Freezing Point Depression, The presence of a solute also lowers the freezing point of a solvent. This happens as the solute particles interfere with the solvent molecules' ability to form a solid structure, meaning the solution must be cooled to a lower temperature to solidify. Osmotic Pressure, This property refers to the pressure required to stop the solvent's flow across a semipermeable membrane from a dilute solution to a more concentrated one. Osmotic pressure is direct evidence of the presence of solute particles and is proportional to the concentration of the solute.

    ...view full instructions

    What is the effect of a non-volatile solute on the vapor pressure of a solution?

    Solution

    According to Raoult’s law, adding a non-volatile solute to a solvent reduces the solvent’s vapor pressure. The solute particles occupy the solution’s surface, decreasing the number of solvent molecules that can escape into the vapor phase.

    Correct answer: B: It decreases the vapor pressure.

  • Question 10
    5 / -1

    Directions For Questions

    Read the following passage carefully:

    Colligative properties are those properties of a solution that depend on the number of particles of the solute dispersed in the solvent, not on the nature of the chemical species present. These properties provide important insight into understanding the behavior of solutions and have practical applications in various fields, including chemistry and biochemistry. The four main colligative properties are vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure. Vapor Pressure Lowering, When a non-volatile solute is dissolved in a solvent, the vapor pressure of the solvent decreases. This is because the solute particles occupy space on the surface of the solution, making fewer solvent molecules available to escape into the vapor phase. Boiling Point Elevation, The addition of a solute to a solvent increases the solution's boiling point. This elevation occurs because the lowered vapor pressure requires a higher temperature to reach the atmospheric pressure, necessitating additional heat. Freezing Point Depression, The presence of a solute also lowers the freezing point of a solvent. This happens as the solute particles interfere with the solvent molecules' ability to form a solid structure, meaning the solution must be cooled to a lower temperature to solidify. Osmotic Pressure, This property refers to the pressure required to stop the solvent's flow across a semipermeable membrane from a dilute solution to a more concentrated one. Osmotic pressure is direct evidence of the presence of solute particles and is proportional to the concentration of the solute.

    ...view full instructions

    Osmotic pressure is a colligative property that demonstrates:

    Solution

    Osmotic pressure (π \pi π) is a colligative property that measures the pressure needed to prevent solvent flow across a semipermeable membrane from a dilute to a concentrated solution. It is given by:

    π = iCRT

    Where π is the osmotic pressure, i is the van’t Hoff factor, M is the molar concentration, R is the universal gas constant and T is the temperature. Osmotic pressure is directly proportional to solute concentration, reflecting the presence of solute particles.

    Correct answer: D: The presence of solute particles and is proportional to solute concentration.

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