HESI A2 Elsevier (HESI): HESI Admission Assessment - Set 5 - Part 2

Correct Answer: Very low on the pH scale

Strong acids fully ionize in water, which produces many free hydrogen ions in solution. This abundance of hydrogen ions gives strong acid solutions a very low pH near the bottom of the scale. Option b is incorrect because Neutral pH lies at the middle of the scale and applies to pure water at room temperature. Strong acids do not have a neutral pH because they have abundant free hydrogen ions in solution. Option c is incorrect because A high pH near the top of the scale describes strong bases in solution rather than acids. Strong acids sit at the opposite extreme of the pH scale due to their abundant hydrogen ions. Option d is incorrect because Although temperature can shift pH slightly during measurement, strong acid pH does not change randomly. Strong acid solutions consistently exhibit very low pH values across the normal range of temperatures encountered in lab work.

Correct Answer: Feel slippery to the touch

Bases feel slippery because they react with skin oils to form soap like substances on contact. This slippery quality is one of the recognized characteristics that distinguishes bases from acids in solution and laboratory work. Option a is incorrect because Sour taste is characteristic of acids, such as those found in citrus fruits and vinegar at home. Bases instead tend to taste bitter rather than sour, although tasting any unknown chemical substance is unsafe. Option b is incorrect because Turning blue litmus red is a classic acid response on indicator paper during chemistry tests. Bases do the opposite by turning red litmus blue, which is one of the standard tests for bases. Option c is incorrect because Producing hydrogen gas through reaction with active metals is typical of acids reacting with metals like zinc. Bases generally do not generate hydrogen gas when in contact with metals under normal aqueous conditions.

Correct Answer: Salt and water

Acid and base neutralization produces a salt and water as the main products of the reaction. The hydrogen ion combines with hydroxide to make water, while the remaining ions form the salt together. Option a is incorrect because Neutralization consumes the acidic and basic species rather than creating a new acid in solution. The reaction yields a neutral or near neutral mixture of salt and water as products, not a fresh acid. Option c is incorrect because Pure metals and gases are not typical products of neutralization reactions in chemistry. Such products may appear in single replacement or decomposition reactions, but they are not made by an acid base neutralization. Option d is incorrect because Metal oxides may behave as bases in chemistry under certain conditions, but they are not products of typical aqueous neutralization. The standard products of acid base neutralization are simply a salt and water.

Correct Answer: Resists pH changes from acids or bases

A buffer contains a weak acid and its conjugate base in solution together. These components neutralize added acids or bases, which resists pH changes and helps maintain a stable solution environment for living cells. Option a is incorrect because Buffers do not eliminate dissolved ions from solution at all in chemistry. They contain a weak acid and its conjugate base, both of which remain in solution to neutralize any added acids or bases. Option b is incorrect because Buffers act to oppose pH changes in either direction rather than to increase acidity quickly. They counteract added hydrogen or hydroxide ions to keep the pH within a narrow stable range that supports life. Option d is incorrect because Buffers maintain pH within a narrow range, but not necessarily at exactly neutral pH. The buffered pH depends on the specific weak acid and conjugate base used, and many useful buffers are not neutral.

Correct Answer: The pH decreases

Higher hydrogen ion concentration means a more acidic solution, and acidic solutions have lower pH values. Therefore an increase in hydrogen ion concentration always produces a corresponding decrease in pH within any aqueous mixture. Option b is incorrect because If hydrogen ion concentration changes in solution, the pH must change as well during the chemical change. The pH cannot remain unchanged whenever the concentration of hydrogen ions shifts in either direction at all. Option c is incorrect because Maximum pH values correspond to very low hydrogen ion concentrations, which is the opposite condition from the question. Increasing hydrogen ions moves pH lower, not toward the high end of the standard pH scale. Option d is incorrect because Negative pH values occur only at very high hydrogen ion concentrations, not at very low concentrations of hydrogen ions. The relationship between increased hydrogen ions and decreased pH is the central concept tested here.

Correct Answer: The loss of electrons

Oxidation is defined as the loss of electrons by a chemical species during a redox reaction in chemistry. The substance that loses electrons becomes more positively charged and is paired with a reducing agent. Option a is incorrect because Proton gain refers to acid base behavior of a chemical species in solution, not oxidation. Oxidation and reduction are defined strictly by electron transfer between species rather than by the movement of protons. Option b is incorrect because Neutron gain occurs in nuclear processes and changes the isotope of an atom rather than its oxidation state. Neutron movement is not part of the definition of oxidation, which involves only electron loss. Option c is incorrect because Gaining electrons is the definition of reduction, which is the opposite of oxidation in chemistry. The two processes always occur together in redox reactions, with one substance oxidized and another reduced at once.

Correct Answer: The species that gains electrons

Reduction is defined as the gain of electrons by a chemical species during a redox reaction. The species that gains electrons becomes more negative and is called the oxidizing agent because it pulls electrons in. Option a is incorrect because Losing electrons defines oxidation, which is the opposite of reduction during a redox reaction. The species that loses electrons becomes more positive in charge and is called the reducing agent because it donates electrons. Option c is incorrect because Proton gain belongs to acid base chemistry rather than redox chemistry in solution. Redox is identified strictly by electron transfer, with reduction marked by the gain of electrons rather than the gain of protons. Option d is incorrect because Light emission may accompany some redox reactions in chemistry under specific conditions, but it is not the defining feature of reduction. Reduction is defined strictly by electron gain regardless of any light emitted.

Correct Answer: NAD

NAD is an electron carrier coenzyme that picks up electrons during cellular respiration in cells. It delivers those electrons to the electron transport chain, which enables efficient energy capture in living cells everywhere. Option a is incorrect because Hemoglobin is a protein that carries oxygen and carbon dioxide in the blood between lungs and tissues. Its role is gas transport rather than electron transfer during the energy capturing reactions of cellular respiration. Option b is incorrect because Insulin is a hormone that regulates blood glucose levels by signaling cells to absorb sugar from circulation. It does not carry electrons or participate directly in cellular respiration or the electron transport chain. Option d is incorrect because Collagen is a structural protein that provides strength and support in connective tissue throughout the body. It plays no role in carrying electrons or supporting metabolic energy production in any aerobic or anaerobic pathway.

Correct Answer: Carbohydrates

Carbohydrates such as glucose are the primary source of quick energy because they are rapidly broken down through glycolysis. Cellular respiration produces usable energy molecules promptly, and the body can mobilize stored glycogen. Option b is incorrect because Nucleic acids store and transmit genetic information rather than serving as fuel for cells. Their function is informational rather than energetic, so they are not used as a quick or slow energy source. Option c is incorrect because Lipids store energy densely for long term use rather than supplying quick energy to cells. They are mobilized when carbohydrate stores are low, providing sustained but slower release of usable fuel for the body. Option d is incorrect because Structural proteins build and maintain tissues throughout the body rather than serving as fuel for cells. Proteins are used for energy only as a last resort during prolonged starvation when other fuel sources are gone.

Correct Answer: They always occur together as paired processes

Oxidation and reduction always occur together as paired processes during any redox reaction in chemistry. Electrons lost by the oxidized species are gained by the reduced species, which makes them coupled halves together. Option a is incorrect because Oxidation and reduction are not separate processes in two different reactions during a redox event. They are paired processes in which electrons released by one species are captured by another species nearby. Option b is incorrect because Precipitate formation is unrelated to oxidation in a redox reaction within solution. Many redox reactions occur entirely in solution or in the gas phase without producing any precipitate, so oxidation does not require one. Option c is incorrect because Reduction is not limited to any particular phase of matter during a chemical reaction in chemistry. It can occur in solid, liquid, gas, or solution states wherever electron transfer takes place between species.

Correct Answer: Speed is scalar, velocity is vector

Speed is a scalar quantity with magnitude only, while velocity is a vector quantity with both magnitude and direction. This distinction is important in physics whenever motion needs to be described accurately and fully. Option a is incorrect because Speed and velocity are not identical quantities in physics during the description of motion. They share magnitude but differ because velocity also specifies direction of motion, which makes them distinct quantities in mechanics. Option b is incorrect because Neither speed nor velocity is a force or an energy in physics during the description of motion. Both quantities describe how fast an object moves through space, with velocity adding a directional component. Option d is incorrect because Mass is not part of either definition in physics during the description of motion. Speed and velocity describe motion regardless of the mass of the object, with velocity differing from speed by direction.

Correct Answer: First law, the law of inertia

Newton's first law states that an object in motion stays in motion at constant velocity unless acted on by a net external force. The passenger continues forward by inertia when the car stops. Option b is incorrect because Newton's second law relates net force, mass, and acceleration through a simple proportional relationship in physics. While related to motion, it does not specifically explain the inertial tendency of a body to keep moving. Option c is incorrect because Newton's third law concerns equal and opposite forces between two interacting bodies that act on each other. It does not directly explain why a passenger continues forward when the vehicle around them halts. Option d is incorrect because Universal gravitation describes the attractive force between masses across distance in space throughout the universe. It does not address why a passenger continues moving forward when the surrounding car suddenly stops in traffic.

Correct Answer: Straight line from start to end

Displacement is the straight line distance and direction from the starting point to the ending point of a journey. Unlike distance, displacement is a vector quantity with both magnitude and direction together. Option a is incorrect because Total path length traveled describes distance, which is a scalar quantity in physics. Displacement differs because it measures only the straight line between starting and ending points, not the full path traveled. Option b is incorrect because Time spent moving is a measurement of duration during the journey, not a measurement of position change. Displacement specifically refers to a change in location measured between the starting and ending points directly. Option c is incorrect because Mass times velocity defines momentum, not displacement, in classical physics during the study of motion. Momentum involves how much motion an object carries, while displacement involves how far and in what direction it moved.

Correct Answer: The third law

Newton's third law states that whenever one object exerts a force on another, the second object exerts an equal and opposite force back on the first. These paired action and reaction forces always coexist. Option a is incorrect because Newton's first law describes inertia, which is the tendency of objects to maintain their current state of motion. It does not address the paired forces that arise between two interacting bodies during contact. Option c is incorrect because Newton's second law relates net force to mass and acceleration through a simple proportional relationship in physics. It explains how forces produce changes in motion of an object, but does not address paired forces. Option d is incorrect because Conservation of energy is a separate physical principle stating that energy cannot be created or destroyed during any process. It is not one of Newton's laws of motion, and it does not describe paired forces.

Correct Answer: Force that opposes motion of surfaces

Friction is a contact force that opposes the relative motion of surfaces in contact with each other. It arises from microscopic interactions between the surfaces and acts opposite to the direction of motion. Option a is incorrect because Friction does not speed up motion of an object during contact with a surface. It always acts opposite to the direction of motion or to the tendency of motion, so friction slows objects down. Option b is incorrect because Stored chemical energy resides within the bonds of substances and is unrelated to friction at any scale. Friction is a contact force that arises between surfaces in contact, not a form of potential energy. Option d is incorrect because Friction is a force, not a wave that travels through any material. While vibrations may pass through solids as sound or other mechanical waves, that phenomenon is unrelated to the contact force of friction.

Correct Answer: Elastic potential energy

A stretched or compressed spring stores elastic potential energy due to its deformation away from the natural rest length. The energy is held in the deformation and is released when the spring relaxes. Option b is incorrect because Thermal energy relates to particle motion and temperature within a material, not to spring deformation in any way. While friction may produce some heat during the motion of the spring, the main energy is elastic. Option c is incorrect because Chemical energy is held in the bonds between atoms within a substance during chemical reactions. A stretched spring stores energy through deformation of its overall shape rather than through any chemical bond change. Option d is incorrect because Nuclear energy is held within atomic nuclei and is released only through nuclear processes such as fission or fusion. Mechanical stretching of a spring does not involve any nuclear energy storage at all.

Correct Answer: Energy of an object due to motion

Kinetic energy is the energy that an object possesses due to its motion through space at a given speed. The faster the object moves and the greater its mass, the more kinetic energy it carries. Option a is incorrect because Energy stored in chemical bonds is chemical potential energy, not kinetic energy at all in physics. Chemical energy can be released during chemical reactions but is not associated with the motion of an object. Option b is incorrect because Energy due to position in a gravitational field is gravitational potential energy, not kinetic energy in physics. Gravitational potential energy depends on height and gravity rather than on the motion of the object. Option c is incorrect because Nuclear energy is contained within the atomic nuclei of substances and is released through nuclear reactions like fission. Nuclear energy is unrelated to the energy that an object possesses simply because it is moving.

Correct Answer: Force applied through a distance

Work in physics is done when a force acts on an object and moves it through a distance in the direction of the force. Without motion in that direction, no work is done at all. Option a is incorrect because Time spent thinking about a problem is not work in the physics sense at all. Physics defines work very specifically in terms of force and motion of an object rather than in terms of effort. Option c is incorrect because Mass times gravity gives weight, the gravitational force on an object at a particular location in space. Weight is itself a force rather than work, and it does not by itself imply any motion. Option d is incorrect because Heat absorbed during a phase change is latent heat, which is related to thermal energy rather than to mechanical work. Work in physics involves force acting through a displacement of the object instead.

Correct Answer: Total momentum stays constant in isolation

Conservation of momentum states that in an isolated system with no external force acting on it, the total momentum before and after any interaction within the system remains exactly the same value. Option a is incorrect because Momentum does not increase without bound during a collision in any isolated system in physics. In an isolated system without external forces acting from outside, the total momentum stays the same overall after impact. Option b is incorrect because Momentum does not disappear during a collision in any isolated system in physics. Momentum is conserved as a vector quantity, although it may transfer between the colliding objects, so the total momentum remains. Option d is incorrect because Momentum is not equal to any heat that is lost during a collision in physics during the impact. Heat is a form of thermal energy that flows due to temperature differences, while momentum tracks motion.

Correct Answer: Depends on masses and distance

Gravitational force depends on the masses of the two interacting objects and the distance between their centers. Greater masses produce stronger attraction, while greater separation produces weaker attraction between any two bodies. Option b is incorrect because Mass strongly influences gravitational force between objects in space throughout the universe. Larger masses produce stronger gravitational attraction toward each other, so the gravitational force between two objects is not identical for all pairs. Option c is incorrect because Gravitational force exists between all objects with mass, from subatomic particles up to planets and stars throughout the universe. It is not limited to any particular size scale of interacting bodies in nature. Option d is incorrect because Gravitational force acts on objects whether they are moving or stationary in space throughout the universe. Motion is not required for gravity to attract two masses toward one another in space at any time.