HESI A2 Chemistry Questions

Correct Answer: A

Rationale: Acids have a sour taste due to their ability to release hydrogen ions (H+) in solution. This sour taste is a key characteristic property of acids. Bitter taste (Choice B) is associated with bases, not acids. Reacting with bases (Choice C) is a general property of acids, not a characteristic property. Slippery feel (Choice D) is an attribute of bases, not acids. Thus, the correct answer is A because of the unique sour taste exhibited by acids.

Correct Answer: C

Rationale: The correct answer is C: Ammonia. Ammonia is a base because it can accept protons (H+ ions) to form ammonium ions (NH4+). It can also react with water to form ammonium hydroxide, which is a strong base. Water (choice A) is neutral, not a base. Sodium chloride (choice B) is a salt formed from the reaction of a strong acid and a strong base, not a base itself. "Salt" (choice D) is a general term for any ionic compound formed from the neutralization of an acid and a base, not specifically a base.

Correct Answer: B

Rationale: The correct answer is B: Ionic bond. Sodium chloride is formed when sodium, a metal, transfers its electron to chlorine, a non-metal, resulting in the formation of Na+ and Cl- ions that are held together by electrostatic forces, forming an ionic bond. In an ionic bond, electrons are transferred from one atom to another, leading to the attraction between oppositely charged ions. Covalent bonds (choice A) involve sharing of electrons between atoms, which is not the case in sodium chloride. Metallic bonds (choice C) involve sharing of electrons in a sea of delocalized electrons within a metal lattice, which is not present in sodium chloride. Hydrogen bonds (choice D) are weaker intermolecular forces that occur between molecules containing hydrogen bonded to highly electronegative atoms like oxygen or nitrogen, which is not relevant to the bonding in sodium chloride.

Correct Answer: D

Rationale: The correct answer is D: Baking soda. Baking soda, or sodium bicarbonate, has a pH value greater than 7, typically around 8.4 when dissolved in water. This is because it is a basic compound that releases hydroxide ions when dissolved in water, resulting in a pH above 7. In contrast, choices A, B, and C have pH values below 7. Water (choice A) is neutral with a pH of 7, vinegar (choice B) is acidic with a pH below 7, and lemon juice (choice C) is also acidic due to the presence of citric acid. Therefore, baking soda is the only substance among the choices that has a pH value greater than 7.

Correct Answer: A

Rationale: The correct answer is A: mass spectrometer. A mass spectrometer separates gaseous ions based on their mass-to-charge ratio by ionizing the sample, accelerating the ions, and then analyzing their deflection in a magnetic field. This process allows for the determination of the molecular weight of compounds. B: Interferometer measures interference patterns, not mass-to-charge ratios. C: Magnetometer measures magnetic fields, not ion mass-to-charge ratios. D: Capacitance meter measures capacitance, not mass-to-charge ratios.