DAT Question of the Day

Correct Answer: A.

Molarity = Moles per liter of solution.

Moles = mass/molecular mass = 100/(23.0 + 35.5)

Volume is in liters: 500ml = 0.500 Liters

Molarity =

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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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Correct Answer: A. waft the air toward your nose

If it is necessary to smell a chemical in the lab, the proper procedure is to waft the air toward your nose using a cupped hand. You should never place your nose directly over the chemical to avoid chemical burns to your respiratory structures. It is not advised to tilt the flask to smell a chemical as you increase the chances of spilling the chemical.

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Correct Answer: B. 12 atmospheres

This is a Dalton’s partial pressure question. According to Dalton’s Partial pressure law, the total pressure of a mixture of gases can be determined by adding the individual pressures of the gas. In this problem, the total pressure is 48 atmospheres (atms) and 75% or 3/4ths of the pressure is accounted for by the largest and smallest gases. The two remaining gases must there for account for only 25% of the total pressure. Therefore, 25% of 48 is equal to 12.

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Correct Answer: E. They all have a valence shell configuration of s²p⁵

The group 7A elements are often referred to as the halogens. This is a diverse group of elements as some are gases under standard conditions (F2, Cl2) while others are liquids (Br) and still others are solids (I and At). The only elements in this group that are diatomic are: fluorine, chlorine, bromine, and iodine. They also span a range of element classifications, with both non-metals and metalloids represented in the family. The only characteristic that is true for all elements in group 7A is that they all have an outer-shell electron configuration of s²p⁵, resulting in a total of 7 valence electrons.

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Correct Answer: D. Group 18 (VIIIA or O) – Inert Gases

The Group 18 (VIIIA or O) – Inert Gases elements, He, Ne, Ar, Kr, Xe and Rn are all monatomic, chemically unreactive gases that possess the stable electron configurations that all Representative elements try to attain by undergoing chemical reactions.

The alkali Metals, Alkaline Earth Metals and Halogens are all chemically active and react in such ways as to attain the same number of electrons as their nearest Inert Gas.

The Transition Metals are not a Group on the Periodic Table, but represent the filling of the 3 – 6 d sub-shells. Their chemistry is not determined by the Inert Gases.

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