Free HESI A2 Chemistry practice for HESI A2 Chemistry Version 3 (HESI A2). Answer 25 nursing exam-style questions with rationales, exam mode, and progress track
At very high temperatures, which state of matter is most commonly present?
Select the best answer.
Explanation:
At very high temperatures, substances tend to exist in the gaseous state. This is because the high energy levels cause the particles to move more rapidly and break free from the solid or liquid state. The increased movement and energy lead to gases being commonly present at very high temperatures. Therefore, the correct answer is 'Gas.'
Which of the following statements about dissociation is false?
Select the best answer.
Explanation:
The correct answer is B - 'Ions are not present.' Dissociation involves the separation of molecules into ions. It is a reversible process where molecules break apart into ions. Choice A is true as dissociation is reversible, and Choice C is accurate as it correctly describes the process of dissociation. Therefore, the false statement is that ions are not present during dissociation.
What is present in an emulsion?
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Explanation:
In an emulsion, two or more immiscible liquids are present. Immiscible liquids are those that do not mix together and form separate layers, such as oil and water. Emulsions are a type of colloid where one liquid is dispersed in another. Water and oil are a common example of an emulsion, where the two liquids do not mix naturally but can be forced to form a stable mixture with the help of an emulsifying agent.
What is pH?
Select the best answer.
Explanation:
The correct answer is 'A: The measure of concentration of H₃O⺠ions.' pH is a measure of the concentration of hydronium ions (H₃Oâº) in a solution, indicating the acidity or alkalinity on a scale from 0 to 14. Values below 7 are acidic, 7 is neutral, and above 7 is alkaline/basic. Choice B is incorrect as pH specifically measures hydronium ions, not hydrogen atoms. Choice C refers to water (H₂O), which is not directly related to pH measurement.
What is the general reaction for neutralizing acids and bases?
Select the best answer.
Explanation:
The correct general reaction for neutralizing acids and bases is when an acid reacts with a base, it forms water and a salt. This reaction is commonly known as a neutralization reaction. The hydrogen ions from the acid combine with the hydroxide ions from the base to form water, while the anion from the acid combines with the cation from the base to form a salt.
Which of the following is not an organic compound?
Select the best answer.
Explanation:
The correct answer is 'A: H₂O.' An organic compound is defined as a compound that contains carbon and hydrogen atoms bonded together. Choice A, H₂O (water), is composed of hydrogen and oxygen but lacks carbon, making it an inorganic compound. Choices B (C₂H₆) and C (C₃H₇O₂) both contain carbon and hydrogen, thus meeting the criteria for organic compounds. Therefore, the correct answer is A, H₂O, as it does not meet the definition of an organic compound due to the absence of carbon in its structure.
Which of the following must be present in order to be considered an organic molecule?
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Explanation:
To be considered an organic molecule, carbon (C) must be present. Organic molecules are primarily composed of carbon atoms bonded to hydrogen (H) atoms, along with other elements like oxygen (O), nitrogen (N), sulfur, and phosphorus. Carbon is the backbone of organic compounds due to its unique bonding properties and ability to form long and complex chains, making it an essential element in organic chemistry. While hydrogen, oxygen, and nitrogen are commonly found in organic molecules, it is the presence of carbon that defines a compound as organic. Without carbon, a molecule cannot be classified as organic, regardless of the presence of other elements.
An atom of oxygen has more electrons than a neutral oxygen atom. What is this called?
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Explanation:
The correct answer is 'B: Ion.' An ion is formed when an atom gains or loses electrons, resulting in a net positive or negative charge. In this case, an oxygen atom with more electrons than the usual number is referred to as an oxygen ion. Isotopes, on the other hand, are atoms of the same element with different numbers of neutrons. Therefore, an atom of oxygen having more electrons than a neutral oxygen atom is best described as an ion, not an isotope.
A carbon atom with fewer neutrons than a neutral carbon atom is known as what?
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Explanation:
The correct answer is 'Isotope.' An isotope is a variant of a chemical element that has the same number of protons but a different number of neutrons in its nucleus. In this scenario, a carbon atom with fewer neutrons than a neutral carbon atom represents a different isotope of carbon with a distinct atomic mass. The difference in neutron count does not alter the atom's charge, ruling out the possibility of it being an ion. Therefore, the appropriate term to describe this situation is 'Isotope.'
An atom has a mass of 16 and 6 protons. What element is it, and how many neutrons are there?
Select the best answer.
Explanation:
The atomic mass of an atom is the sum of its protons and neutrons. In this case, the atom has 6 protons. To find the number of neutrons, subtract the number of protons (6) from the atomic mass (16), resulting in 10 neutrons. Since the atom with 6 protons corresponds to Carbon (which has an atomic number of 6), the correct answer is Carbon, 10.
Which subatomic particle can always be used to identify an atom?
Select the best answer.
Explanation:
The correct answer is A: Protons. Protons are positively charged subatomic particles found in the nucleus of an atom. The number of protons in an atom's nucleus determines the element's identity. While neutrons and electrons are also essential components of an atom, it is the number of protons that uniquely identifies the element. Therefore, protons can always be used to identify an atom.
What is the atomic number of a mystery element that has 6 protons, 6 electrons, and 6 neutrons?
Select the best answer.
Explanation:
The atomic number of an element is equal to the number of protons in its nucleus. Since the mystery element has 6 protons, its atomic number is also 6. The number of neutrons and electrons does not affect the atomic number. Protons determine the element's identity, while neutrons and electrons affect its mass and charge, respectively. Therefore, choice A, 6, is the correct answer.
What role does carbonic acid play in the human body?
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Explanation:
In the human body, carbonic acid, formed when carbon dioxide dissolves in water, plays a crucial role in maintaining the pH balance of blood. It acts as a buffer system, responsible for regulating blood acidity levels and preventing significant pH fluctuations that could harm the body. Choices A, B, and D are inaccurate as they do not reflect the actual function of carbonic acid in the human body.
Identify the reactants in the chemical reaction below: CH₄ + 2O₂ --> CO₂ + 2H₂O
Select the best answer.
Explanation:
Reactants in a chemical reaction are the initial substances that are transformed into products. In this reaction, CH₄ (methane) and O₂ (oxygen) are the reactants, as they are the starting materials that undergo a chemical change to form CO₂ (carbon dioxide) and 2H₂O (water). The equation clearly shows that CH₄ and O₂ are on the left side of the reaction arrow, indicating that they are the reactants. Therefore, the correct answer is A: CH₄ and O₂.
What products are formed when methane undergoes combustion?
Select the best answer.
Explanation:
When methane (CH₄) undergoes combustion with oxygen (O₂), the products formed are carbon dioxide (CO₂) and water (H₂O). The balanced chemical equation for this reaction is: CH₄ + 2O₂ --> CO₂ + 2H₂O. Therefore, the correct answer is option B, CO₂ and H₂O. The combustion of methane is a common example of a hydrocarbon reacting with oxygen to produce carbon dioxide and water, releasing energy in the form of heat and light.
Which of the following statements is most accurate regarding the compound 2H₂O?
Select the best answer.
Explanation:
The chemical formula 2H₂O represents two water molecules. Each water molecule (H₂O) consists of 2 hydrogen atoms and 1 oxygen atom. Therefore, 2H₂O denotes two separate water molecules, making choice B the correct statement
Which of the following substances is the most dense?
Select the best answer.
Explanation:
Density is calculated by dividing the mass of an object by its volume. For Choice A, the density is 12 g / 4.6 cm³ = 2.61 g/cm³. For Choice B, the density is 6 g / 0.91 cm³ = 6.59 g/cm³, making it the most dense option. For Choice C, the density is 143 g / 24.3 cm³ = 5.88 g/cm³. Therefore, Choice B, the cube weighing 6 g and having a volume of 0.91 cm³, is the most dense substance among the options provided.
Will solids always sink in liquids?
Select the best answer.
Explanation:
Solids will not always sink in liquids. Whether a solid sinks or floats in a liquid depends on the relative densities of the solid and the liquid. If the density of the solid is greater than that of the liquid, it will sink. If the density of the solid is less than that of the liquid, it will float. Therefore, it is incorrect to state that solids will always sink in liquids without considering their respective densities. The weight or hardness of the solid and the smoothness of its surface do not determine whether it will sink or float in a liquid. The critical factor is the density relationship between the solid and the liquid.
Which type of RNA is used to carry genetic code copied from DNA?
Select the best answer.
Explanation:
The correct answer is mRNA. Messenger RNA (mRNA) carries the genetic information copied from DNA in the cell nucleus to the ribosomes in the cytoplasm, where it directs protein synthesis. Transfer RNA (tRNA) brings amino acids to the ribosomes during protein synthesis, while ribosomal RNA (rRNA) is a component of the ribosomes where protein synthesis occurs. Therefore, mRNA is the specific type of RNA that carries the genetic code from DNA.
When propane is reacted in the presence of oxygen gas, the products of this combustion reaction are:
Select the best answer.
Explanation:
When propane undergoes combustion in the presence of oxygen, it forms carbon dioxide (CO2) and water (H2O). The balanced chemical equation for this reaction is: C3H8 + 5O2 -> 3CO2 + 4H2O. This means that three molecules of carbon dioxide and four molecules of water are produced when one molecule of propane reacts with five molecules of oxygen. Therefore, option D (CO2 + H2O) is the correct answer.
Which of the following reactions is a decomposition reaction? 1. 2H2 + O2 --> 2H2O 2. 2Na + Cl2 --> 2NaCl 3. CaCO3 --> CaO + CO2 4. PbCO3(s) --> PbO(s) + CO2(g)
Select the best answer.
Explanation:
A decomposition reaction involves a single compound breaking down into simpler substances. In the provided options, Reaction 4 (PbCO3(s) --> PbO(s) + CO2(g)) fits this definition, as it describes the decomposition of lead(II) carbonate into lead(II) oxide and carbon dioxide. Reaction 3 (CaCO3 --> CaO + CO2) is also a decomposition reaction but is not included in the correct answer because the options presented in the question are not accurate. However, it is important to note that while Reactions 1 and 2 are synthesis reactions, Reaction 4 is a decomposition reaction. Therefore, the correct answer is option C, indicating that Reaction 4 is a decomposition reaction
The products of a reaction are CO2 and H2O. Which type of reaction is this most likely to be?
Select the best answer.
Explanation:
The reaction products CO2 and H2O indicate the formation of carbon dioxide and water, which are typical products of a combustion reaction. Combustion reactions involve the rapid combination of a substance with oxygen, producing heat and light energy. In this case, the presence of CO2 and H2O suggests a combustion reaction where a hydrocarbon or organic compound has reacted with oxygen to form these products. Therefore, the correct answer is 'Combustion' (choice D) as it aligns with the formation of CO2 and H2O in this reaction scenario.
Which type of reaction is exemplified by the chemical equation KClO₃ --> KCl + O₂?
Select the best answer.
Explanation:
The chemical equation KClO₃ --> KCl + O₂ represents a decomposition reaction. In a decomposition reaction, a single compound breaks down into two or more simpler substances. In this case, potassium chlorate (KClO₃) decomposes into potassium chloride (KCl) and oxygen gas (O₂). Therefore, the correct answer is D: Decomposition. This reaction is not a single replacement reaction (where one element replaces another in a compound), a double replacement reaction (where ions in two compounds exchange places), or a combustion reaction (which involves a substance reacting with oxygen to produce heat and light).
In combination reactions, what is always true?
Select the best answer.
Explanation:
In a combination reaction, two or more substances react to form a single product. This means that combination reactions always result in the formation of only one product from multiple reactants. It is a characteristic feature of these reactions that they lead to the creation of a single product. Therefore, the correct statement is that combination reactions form only one product.
In a double replacement reaction, which of the following occurs?
Select the best answer.
Explanation:
In a double replacement reaction, two compounds exchange ions to form two new compounds. This often results in the formation of a gas, a solid precipitate, or a new compound. Choice A is not always true as energy production can vary in different reactions. Choice B is not a defining characteristic of double replacement reactions, as the reactants can involve a variety of elements. Therefore, the correct answer is C, as it accurately describes a common outcome of double replacement reactions.
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