which is a property of an ionic compound

HESI A2

Chemistry HESI A2 Practice Test

1. Which is a property of an ionic compound?

A. Low melting point
B. Poor conductivity
C. Shared electrons
D. Crystalline shape

Correct answer: D

Rationale: Ionic compounds are composed of positively and negatively charged ions that are held together by strong electrostatic forces. These ions arrange themselves in a repeating pattern to form a stable and orderly structure known as a crystalline shape. This is a characteristic property of ionic compounds, making choice D the correct answer. Choices A, B, and C are incorrect because ionic compounds typically have high melting points, good conductivity in the molten or dissolved state, and do not involve shared electrons but rather the transfer of electrons between atoms.

2. 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.

3. Which of the following represents a hydride ion?

A. H⁻
B. H⁺
C. OH⁻
D. HCl

Correct answer: A

Rationale: The hydride ion is denoted by H⁻, indicating that it has gained an extra electron to complete its valence shell, resulting in a full octet and a net charge of -1. This ion is commonly found in metal hydrides and plays a significant role in various chemical reactions. Option B, H⁺, represents a proton with a positive charge. Option C, OH⁻, represents the hydroxide ion, consisting of oxygen and hydrogen. Option D, HCl, is a compound composed of hydrogen and chlorine ions, not a hydride ion.

4. What is the correct formula for iron III oxide?

A. IO
B. FeS
C. Fe₂O₃
D. OFe₂₃

Correct answer: C

Rationale: The correct formula for iron III oxide is Fe2O3. In this formula, Fe represents iron and O represents oxygen. Iron III oxide consists of two iron (Fe) ions combined with three oxygen (O) ions. Thus, the correct formula is Fe2O3. Choice A (IO) is incorrect as it does not represent the correct combination of iron and oxygen ions. Choice B (FeS) is incorrect as it represents iron sulfide, not iron III oxide. Choice D (OFe₂₃) is incorrect as it does not follow the correct chemical nomenclature for iron III oxide.

5. What is the molarity of a solution containing 45 moles of NaCl in 4 liters?

A. 0.11 M NaCl
B. 0.45 M NaCl
C. 1.8 M NaCl
D. 8.9 M NaCl

Correct answer: A

Rationale: To calculate the molarity of a solution, you use the formula: Molarity (M) = moles of solute / liters of solution. In this case, M = 45 moles / 4 L = 11.25 M. The correct answer is 0.11 M NaCl. Choice B is incorrect as it doesn't match the calculated value. Choice C is also incorrect as it is significantly higher than the correct molarity. Choice D is incorrect as it is excessively high compared to the calculated value.