HESI A2
HESI A2 Chemistry Questions
1. In which state of matter are particles packed tightly together in a fixed position?
- A. Liquid
- B. Solid
- C. Gas
- D. Plasma
Correct answer: B
Rationale: In a 'solid' state, particles are tightly packed in fixed positions, maintaining a definite shape and volume. This arrangement allows solids to maintain a rigid structure. Liquids have particles that are close together but can move past each other, giving them the ability to flow and take the shape of their container. Gases have particles that are far apart and move freely, leading to their ability to expand to fill any container. Plasma is an ionized gas where particles have high energy levels and are not packed tightly together, making it an uncommon state of matter on Earth.
2. Al(NO3)3 + H2SO4 → Al2(SO4)3 + HNO3 is an example of which kind of reaction?
- A. Decomposition reaction
- B. Synthesis reaction
- C. Single replacement reaction
- D. Double replacement reaction
Correct answer: C
Rationale: The given chemical equation represents a single replacement reaction. In this reaction, aluminum (Al) displaces hydrogen in sulfuric acid (H2SO4), forming aluminum sulfate (Al2(SO4)3) and releasing nitric acid (HNO3). Single replacement reactions involve an element replacing another element in a compound, which is evident in this reaction. Choice A, Decomposition reaction, is incorrect because decomposition reactions involve a single compound breaking down into two or more substances. Choice B, Synthesis reaction, is incorrect as it involves the combination of two or more substances to form a more complex compound. Choice D, Double replacement reaction, is also incorrect as it involves an exchange of ions between two compounds to form two new compounds.
3. What is the charge of noble gases?
- A. -1
- B. 0
- C. 1
- D. 2
Correct answer: B
Rationale: The correct answer is B: 0. Noble gases have a charge of 0 because they have full valence shells and are inert. This makes them stable and unreactive, resulting in a charge of 0 as they do not readily gain or lose electrons. Choices A, C, and D are incorrect because noble gases do not typically form ions by gaining or losing electrons, so they do not carry a charge of -1, 1, or 2.
4. What is the correct formula for calcium carbonate?
- A. CaSO₃
- B. CaCO₃
- C. Ca(OH)â‚‚
- D. CH₃OH
Correct answer: B
Rationale: The correct formula for calcium carbonate is CaCO₃, which consists of one calcium (Ca) atom, one carbon (C) atom, and three oxygen (O) atoms. Therefore, choice B, CaCO₃, is the accurate formula for calcium carbonate. Choices A, C, and D do not represent the correct formula for calcium carbonate. Choice A, CaSO₃, is calcium sulfite, not calcium carbonate. Choice C, Ca(OH)₂, is calcium hydroxide, and choice D, CH₃OH, is methanol, none of which are correct formulas for calcium carbonate.
5. What are neutral particles called?
- A. Neutrons
- B. Protons
- C. Electrons
- D. Cations
Correct answer: A
Rationale: Neutral particles, which have no electric charge, are known as neutrons. Neutrons are found in the nucleus of an atom along with protons. Electrons carry a negative charge and orbit the nucleus. Cations are positively charged ions formed by losing electrons. Therefore, the correct answer is 'Neutrons' as they are the neutral particles in an atom, unlike protons, electrons, or cations.
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