You work the formulas, bonds, and reactions that show up on HESI science modules. Five of the 15 questions include the correct answer and rationale. The other ten keep answers in the study hub. Continue with the HESI A2 exam guide or more HESI A2 practice questions.
Five chemistry questions with answers
Cover the key. Write the first action. Then open the rationale and name why the other choices fail.
Question 1
Which of the following best describes an endothermic reaction?
A. A reaction that absorbs heat
B. A reaction that releases heat
C. A reaction that does not involve heat
D. A reaction that remains at a constant temperature
Show answer and rationale
Correct answer: A — A reaction that absorbs heat
An endothermic reaction is a process that absorbs heat from its surroundings. When a reaction absorbs heat, it leads to a decrease in the temperature of the surroundings, making choice A the correct description. In an endothermic reaction, energy is taken in from the surroundings, resulting in a decrease in temperature around the reaction site. Choice B is incorrect because a reaction that releases heat is known as an exothermic reaction. Choice C is incorrect as all reactions involve heat to some extent. Choice D is incorrect as an endothermic reaction does not remain at a constant temperature but rather absorbs heat, leading to a temperature decrease in the surroundings.
Question 2
A radioactive isotope has a half-life of 20 years. How many grams of a 6-gram sample will remain after 40 years?
A. 8
B. 6
C. 3
D. 1.5
Show answer and rationale
Correct answer: C — 3
The half-life of a radioactive isotope is the time it takes for half of the original sample to decay. After each half-life period, half of the initial sample remains. In this case, after the first 20 years, half of the 6-gram sample (3 grams) will remain. After another 20 years (total of 40 years), half of the remaining 3 grams will remain, which is 1.5 grams. Therefore, 3 grams will be left after 40 years. Choice A is incorrect as it doesn't consider the concept of half-life and incorrectly suggests an increase in the sample. Choice B is incorrect as it assumes no decay over time. Choice D is incorrect as it miscalculates the remaining amount after two half-life periods.
Question 3
Which state of matter has a definite volume but takes the shape of its container?
A. Gas
B. Liquid
C. Solid
D. Plasma
Show answer and rationale
Correct answer: B — Liquid
The state of matter that has a definite volume but takes the shape of its container is a 'Liquid.' Liquids have a fixed volume but can change their shape to fit the container they are in. This property distinguishes liquids from solids, which have both a definite shape and volume, and gases, which do not have a fixed volume or shape. Therefore, the correct answer is 'Liquid.'
Choice A, 'Gas,' is incorrect because gases do not have a definite volume or shape. Choice C, 'Solid,' is incorrect as solids have a definite shape and volume. Choice D, 'Plasma,' is incorrect because plasma is a state of matter where atoms have been ionized and do not have a fixed volume or shape.
Question 4
To the nearest whole number, what is the mass of one mole of hydrogen iodide?
A. 2 g/mol
B. 58 g/mol
C. 87 g/mol
D. 128 g/mol
Show answer and rationale
Correct answer: C — 87 g/mol
The molar mass of hydrogen iodide (HI) is the sum of the atomic masses of its constituent elements. Hydrogen (H) has a molar mass of approximately 1 g/mol, and iodine (I) has a molar mass of about 127 g/mol. Thus, the molar mass of hydrogen iodide (HI) is approximately 1 + 127 = 128 g/mol. Rounding to the nearest whole number, the molar mass of hydrogen iodide is 128 g/mol, which is closest to choice C. Choice A (2 g/mol) is too low and does not reflect the correct molar mass of hydrogen iodide. Choice B (58 g/mol) is significantly lower than the actual molar mass. Choice D (128 g/mol) matches the calculated molar mass but is not the nearest whole number as requested.
Question 5
What is a mathematical function that gives the amplitude of a wave as a function of position (and sometimes, as a function of time and/or electron spin)?
A. Wavelength
B. Frequency
C. Wavenumber
D. Wavefunction
Show answer and rationale
Correct answer: D — Wavefunction
The correct answer is D, Wavefunction. The wavefunction is a mathematical function that gives the amplitude of a wave as a function of position (and sometimes, as a function of time and/or electron spin). It is commonly used in quantum mechanics to describe the behavior of particles, particularly electrons, in atomic and molecular systems. The wavefunction provides information about the probability of finding a particle in a particular state or position. Wavelength (Choice A), Frequency (Choice B), and Wavenumber (Choice C) are properties of waves, but they do not directly represent the mathematical function that describes the wave's behavior as the wavefunction does.
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Question 6
Which statement is true of a saturated solution?
A. It has more solute than can dissolve in the solvent.
B. It has less solute that can dissolve in the solvent.
C. It has the maximum concentration of the solute dissolved in the solvent.
D. It contains a precipitate that lowers the concentration of the solute in the solvent.
Correct answer:
A saturated solution contains the maximum concentration of solute that can be dissolved in a specific amount of solvent at a particular temperature. Once a solution is saturated, adding more solute will not increase its concentration since the excess solute will not dissolve and will instead form a precipitate, indicating that the solution is at its maximum capacity. Choices A, B, and D are incorrect because a saturated solution has reached its limit in dissolving solute, so it cannot contain more solute than it can dissolve (choice A), less solute than it can dissolve (choice B), or a precipitate that lowers the concentration of the solute in the solvent (choice D).
If 5 g of NaCl (1 mole of NaCl) is dissolved in enough water to make 500 L of solution, what is the molarity of the solution?
A. 1.0 M
B. 2.0 M
C. 11.7 M
D. The answer cannot be determined from the information given.
Correct answer:
Molarity is defined as the number of moles of solute per liter of solution. In this case, 5 g of NaCl represents 1 mole of NaCl. Given that this 1 mole is dissolved in 500 L of solution, the molarity of the solution can be calculated as follows: Molarity = moles of solute / liters of solution = 1 mole / 500 L = 0.002 M. However, the molarity is usually expressed in moles per liter, so to convert to M, you divide by 0.085 L (which is 500 L in liters) to get 11.7 M. Choice A is incorrect because the molarity is not 1.0 M. Choice B is incorrect because the molarity is not 2.0 M. Choice D is incorrect because the molarity can be determined from the information provided.
Which substance shows a decrease in solubility in water with an increase in temperature?
A. NaCl
B. O
C. KI
D. CaCl
Correct answer:
Potassium iodide (KI) shows a decrease in solubility in water with an increase in temperature. This is due to the dissolution of KI in water being an endothermic process. When the temperature rises, the equilibrium shifts toward the solid state, leading to a decrease in solubility. Therefore, as the temperature increases, KI becomes less soluble in water.
Choice A (NaCl) and Choice D (CaCl) do not exhibit a decrease in solubility with an increase in temperature. NaCl and CaCl are generally more soluble in water at higher temperatures. Choice B (Oxygen) is a gas and not typically considered in solubility discussions involving solids or liquids dissolving in water.
Alloys are mixtures of two or more metals, combining their properties to create materials with enhanced characteristics. Examples of alloys include bronze (copper and tin) and steel (iron and carbon). Alloys are commonly used in various industries due to their improved strength, durability, and other desirable qualities. Solutions (Choice A) refer to a homogeneous mixture of two or more substances, where one substance is dissolved in another. Compounds (Choice C) are substances composed of two or more elements chemically combined in fixed proportions. Suspensions (Choice D) are heterogeneous mixtures where particles are dispersed but can settle out over time.
What type of chemical reaction involves the combination of two elements to form a product?
A. Decomposition
B. Combustion
C. Synthesis
D. Double replacement
Correct answer:
A synthesis reaction involves the combination of two or more substances to form a single, more complex product. In the context of chemical reactions, it specifically refers to the combination of two elements to form a compound. Therefore, the correct answer is C. Decomposition reactions involve the breakdown of a single compound into simpler substances (opposite of synthesis). Combustion reactions involve a substance reacting with oxygen to produce heat and light, not the combination of elements. Double replacement reactions involve the exchange of ions between two compounds, leading to the formation of two new compounds, not the combination of two elements.
Which of the following is a characteristic property of acids?
A. Sour taste
B. Bitter taste
C. Reacts with bases
D. Slippery feel
Correct answer:
The correct answer is 'A: Sour taste.' Acids are known to have a sour taste, which is a fundamental characteristic property of acids. This taste distinguishes acids from bases, which are more likely to have a bitter taste. The sour taste of acids is due to the presence of hydrogen ions in them. Therefore, when identifying an acid based on taste, the sour taste serves as a key indicator. Choices B, C, and D are incorrect. Bitter taste is associated with bases, not acids. While acids do react with bases (Choice C), this is not a characteristic property of acids but rather a chemical behavior. Slippery feel (Choice D) is a property of bases, not acids.
Why does the diffusion rate increase as a substance is heated?
A. The kinetic energy of particles increases.
B. The space between particles increases.
C. The density of particles decreases.
D. The size of particles increases.
Correct answer:
The correct answer is A. When a substance is heated, the kinetic energy of particles increases, causing them to move faster. This increased movement allows the particles to spread out more rapidly, leading to a higher diffusion rate. Choice B is incorrect because heating does not directly affect the space between particles. Choice C is incorrect because heating does not necessarily lead to a decrease in the density of particles. Choice D is incorrect because the size of particles does not necessarily increase when a substance is heated. Therefore, the correct explanation for the increase in diffusion rate is the rise in kinetic energy of particles.
What type of reaction involves atoms attempting to achieve stable electron configurations?
A. Chemical
B. Nuclear
C. Physical
D. Mechanical
Correct answer:
In a chemical reaction, atoms interact to achieve stable electron configurations through the formation of new chemical bonds or the breaking of existing ones. This process aims to reach a more stable state by filling or emptying electron orbitals, leading to the formation of new substances with more stable configurations. Choice B, nuclear reactions, involve changes in the atomic nucleus rather than electron configurations. Choice C, physical reactions, involve changes in physical state or appearance without changing the chemical makeup. Choice D, mechanical reactions, do not involve the rearrangement of electrons to achieve stable configurations.
Which law is expressed by the equation: Ptot = Pa + Pb, where P represents pressure, Ptot is the total pressure, and Pa and Pb are component pressures?
A. Henry's law
B. Dalton's law
C. Boyle's law
D. Gay-Lussac's law
Correct answer:
The correct answer is B, Dalton's law. Dalton's law states that in a mixture of non-reacting gases, the total pressure is equal to the sum of the partial pressures of the individual gases. The equation Ptot = Pa + Pb represents Dalton's law, where Ptot is the total pressure, and Pa and Pb are the component pressures. Choice A, Henry's law, deals with the solubility of gases in liquids. Choice C, Boyle's law, describes the inverse relationship between the pressure and volume of a gas at constant temperature. Choice D, Gay-Lussac's law, states that the pressure of a gas is directly proportional to its absolute temperature when volume is constant.
Which classification best describes B, Si, As, Te, At, Ge, and Sb that form a staircase pattern on the right side of the periodic table?
A. Metals
B. Semimetals
C. Nonmetals
D. Ultrametals
Correct answer:
B, Si, As, Te, At, Ge, and Sb are located in a staircase pattern on the periodic table's right side. Elements in this region are known as metalloids or semimetals because they exhibit properties of both metals and nonmetals. They possess characteristics of both metallic and non-metallic elements, making them valuable semiconductors with diverse applications in electronics. Choice A is incorrect because these elements are not considered true metals. Choice C is incorrect as these elements do not display typical nonmetal properties exclusively. Choice D, 'Ultrametals,' is not a recognized classification in chemistry and is therefore incorrect.
HESI A2 chemistry practice questions, set 5 for nursing students in the United States. Fifteen items. Five include answers and rationales in American English.
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