HESI A2 Chemistry Practice Questions

Correct Answer: A

Rationale: The net charge of an ionic compound is 0 because it consists of positively charged cations and negatively charged anions that balance each other out. Positively charged ions are formed by losing electrons, while negatively charged ions are formed by gaining electrons. In an ionic compound, the total positive charge from cations equals the total negative charge from anions, resulting in a net charge of 0. Other choices are incorrect: B: -1 - Not all ionic compounds have a net charge of -1. C: +1 - Not all ionic compounds have a net charge of +1. D: Variable - While some ionic compounds may have variable charges for transition metals, the net charge of the compound as a whole remains 0 due to the equal number of positive and negative charges.

Correct Answer: C

Rationale: To calculate the molar mass of hydrogen iodide (HI), we add the atomic masses of hydrogen (1 g/mol) and iodine (127 g/mol). Therefore, the molar mass of HI is 1 + 127 = 128 g/mol. Rounding to the nearest whole number, the mass of one mole of hydrogen iodide is 128 g/mol, making choice C (87 g/mol) incorrect. Choices A (2 g/mol) and B (58 g/mol) are also incorrect as they do not reflect the correct molar mass of hydrogen iodide.

Correct Answer: D

Rationale: The correct answer is D: Silicon. Silicon has an atomic mass greater than that of sodium (Na). Sodium has an atomic mass of 22.99 g/mol, whereas silicon has an atomic mass of 28.09 g/mol. Therefore, silicon's atomic mass is greater than that of sodium. Boron (A), oxygen (B), and fluorine (C) all have atomic masses lower than sodium, making them incorrect choices in this context.

Correct Answer: A

Rationale: The correct answer is A: Arrangement of atoms. Allotropes are different forms of the same element with different structures of atoms. This distinction is based on the specific arrangement of atoms in each allotrope, leading to varying physical and chemical properties. Gram atomic mass (B) is related to the weight of an atom, not the arrangement. Physical state (C) refers to the form of matter (solid, liquid, gas), not the atomic structure. Stability (D) may be a factor influenced by the arrangement of atoms, but it is not the primary distinguishing feature among allotropes.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Heating increases kinetic energy of particles. 2. Higher kinetic energy results in faster movement. 3. Faster movement leads to increased collisions. 4. Increased collisions enhance diffusion rate. Summary of incorrect choices: B. Space between particles increasing doesn't directly affect diffusion rate. C. Density of particles decreasing doesn't necessarily impact diffusion rate. D. Size of particles increasing doesn't affect diffusion rate directly.