DAT Question of the Day

Correct Answer: C. HNO3 + H2O -> NO3– + H3O⁺

To act as a Bronsted-Lowry base water must accept a proton from an acid forming the hydronium ion, H3O⁺. This is the case in HNO3 + H2O -> NO3– + H3O⁺.

NH3 + H2O -> NH4⁺ + OH^– – water is acting as a Bronsted-Lowry acid by releasing a H⁺ and forming the hydroxide ion, OH^–.

NaCl(s) + H2O -> Na⁺(aq) + Cl^–(aq) – Water is acting as a solvent.

CuSO4(s) + 5 H2O -> CuSO4.5H2O(s) – Water is incorporating itself into the copper sulfate as water of hydration.

2 H2O -> H3O⁺ + OH^– – Water is undergoing a disproportionation reaction, acting both as an acid and a base to form H3O⁺ and OH^–.

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Correct Answer: B. The second compound is less hydrogen bonding than acetic acid

The boiling temperature of a compound is largely dependent on the steric hindrance of the molecule and its polarity, or hydrogen bonding capability. As steric hindrance and hydrogen bonding increase, boiling point increases. As steric hindrance and hydrogen bonding decrease, boiling point decreases. Initially, it may seem that answer D could be possible. However, a lower molecular weight does not guarantee a lower boiling temperature. For example, ethanol has a lower molecular weight than butane. However, ethanol’s boiling point is about 78°C whereas butane’s boiling point is -1 °C.

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Correct Answer: A.

Structure B has a negative 2 charge on one single nitrogen atom, which is not the best structure. Formal charges should always be minimized in the best Lewis structures. Structure C has five covalent bonds to the central neutral nitrogen atom, which is unreasonable. Structure D has an improper distribution of lone pairs and incorrect formal charges. Structure A is the best structure. It has an overall charge of –1 and the most minimal formal charges possible.

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Correct Answer: B. Linear

This is a straightforward question. Drawing out the molecule, we see that there are no free electrons on N, meaning that it should be a linear, and not trigonal planar, configuration.

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Correct Answer: E. Pb²⁺ + 2Cl^– → PbCl2

The correct reaction should have a net charge of zero, and must be stoichiometrically correct (no extra electrons or elements). Pb has a charge of 2+, and the chlorine ion has a charge of 1-. Although chlorine’s charge is not stated directly, it should be obvious from the periodic table that chlorine has a charge of 1-. Thus, the resulting compound must be PbCl2, with no charge, which is answer E.

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