HESI A2
HESI A2 Chemistry Questions
1. What type of reaction occurs when an acid and a base react to form water and salt?
- A. Neutralization reaction
- B. Decomposition reaction
- C. Combustion reaction
- D. Redox reaction
Correct answer: A
Rationale: A neutralization reaction is the correct answer. In this type of reaction, an acid and a base combine to form water and salt. The acid donates a proton (H+) to the base, forming water, while the remaining ions combine to form a salt. This reaction results in the neutralization of both the acid and the base, hence the name 'neutralization reaction.' Choice B, decomposition reaction, is incorrect because it refers to a reaction where a compound breaks down into simpler substances. Choice C, combustion reaction, is incorrect as it involves a substance reacting with oxygen to produce heat and light. Choice D, redox reaction, is incorrect because it involves the transfer of electrons between reactants.
2. What distinguishes one allotrope from another?
- A. Arrangement of atoms
- B. Gram atomic mass
- C. Physical state
- D. Stability
Correct answer: A
Rationale: Allotropes are different forms of the same element that exist in the same physical state but have different structures. The arrangement of atoms is what distinguishes one allotrope from another, determining their unique properties and characteristics. Gram atomic mass (Choice B) is a constant value for a specific element and does not change between different allotropes. Physical state (Choice C) refers to whether a substance is a solid, liquid, or gas, which can be the same for different allotropes of an element. Stability (Choice D) can vary between different allotropes, but it is not what always differentiates one allotrope from another. Therefore, the correct answer is the arrangement of atoms, as it is the key factor that varies across different allotropes.
3. How many protons does Potassium have?
- A. 18
- B. 19
- C. 20
- D. 21
Correct answer: B
Rationale: Potassium, with the atomic symbol K, has 19 protons, which is equal to its atomic number. The number of protons determines the element's identity, and in the case of Potassium, it is 19. Choice A (18) is incorrect as it does not correspond to Potassium's proton number. Choice C (20) and Choice D (21) are also incorrect as they do not match the actual number of protons in Potassium.
4. What type of bond is an electrostatic attraction between two oppositely charged ions?
- A. Covalent
- B. Metallic
- C. Ionic
- D. Hydrogen
Correct answer: C
Rationale: An ionic bond forms when one atom transfers electrons to another, resulting in the formation of positively and negatively charged ions. The attraction between these oppositely charged ions creates an electrostatic bond, known as an ionic bond. Choice A, covalent bonds, involve the sharing of electrons, not the transfer. Choice B, metallic bonds, occur between metal atoms and involve a 'sea of electrons' that are delocalized. Choice D, hydrogen bonds, are much weaker interactions between hydrogen atoms and other electronegative atoms like oxygen or nitrogen.
5. Which element is a metalloid?
- A. Silicon
- B. Lead
- C. Helium
- D. Aluminum
Correct answer: A
Rationale: The correct answer is 'Silicon.' Silicon is a metalloid, which means it has properties of both metals and nonmetals. It is commonly used in electronic devices due to its semiconductor properties. Lead (Choice B) is a metal, Helium (Choice C) is a noble gas, and Aluminum (Choice D) is a metal.
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