DAT Question of the Day

Correct Answer: C. 2, 3, 5

The strategy here is to identify planes of symmetry and identify the number of chemically unique carbons. Compounds 2, 3, and 5 have this criterion, and thus are possible structures for the mystery compound.

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Correct Answer: A. 6.8 moles

This question requires the use of the ideal gas law: PV = nRT. We are solving for number of moles (n). The temperature in the equation is in Kelvin, so a 22° C room would actually be 295 K approximately. The pressure (P) at sea level is 1 atmosphere. So, (1 atm X 165 L) / (0.082 L atm/K mol X 295 K) = 6.8 moles

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Correct Answer: A. no reaction would occur

Noble gases are inert and do not react under normal conditions. Therefore, the reaction would not take place. In order for a gas to be produced, a chemical reaction would need to occur. The same is true for the color change and the formation of a precipitate as these signal that a chemical change has happened. However, these would not form/occur in this case because the two reactants would not react chemically.

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Correct Answer: D. activated complex

During a chemical reaction, enough energy must be absorbed for the reaction to take place. This is termed the activation energy. At the height of the activation energy is the activated complex, which is an intermediate between the reactant and the product. This forms when the reactants have gained enough energy and have collided with the right orientation to start the reaction. It is this activated complex that has the highest energy of the answer options given.

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Correct Answer: D. Bromine

The valence shell is the outer shell of an element. It is the electrons in the valence shell that interact to form compounds, either ionic or covalent. If the valence shell ends in the 4th energy level, this means the compound must be in the fourth row of the periodic table, therefore eliminating answer options A, B, and E. The valence shell shows a total of 7 valence electrons, 2 from the s and 5 from the p. The only element that has 7 valence electrons and is in the 4th row is Bromine (Br).

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Correct Answer: D. N2

A purely covalent bond has no difference in electronegativity between the two bonding elements. Thus, N2 is a purely covalent bond. The other answers all have two elements with differing electronegativity, meaning the bond should have some amount of ionic character.

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Correct Answer: C. The sum of the partial pressures of all gases, Dalton’s law of partial pressure

In a mixture of gases, the total gaseous pressure is the sum of the partial pressures of all gases, according to Dalton’s law of partial pressure.

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Correct Answer: E. Pressure, volume and internal energy

The correct answer is E. The equation that governs enthalpy for a homogenous system (all gas or all liquid) is H = U + PV, where U is internal energy, P is pressure, and V is volume.

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Correct Answer: A. A 3D network lattice of covalently bonded carbon atoms.

Diamond is a 3D network lattice of covalently bonded carbon atoms, far right.

Graphite, another allotrope of carbon, is a 2D network lattice of covalently bonded carbon atoms, left.

A 3D network lattice of carbon ions held together by ionic bonds. Does not exist, as carbon does not form ions and elements cannot be ionic, only compounds can.

A 3D network lattice of carbon ions in a sea of mobile valence electrons held together by metallic bonds. This description is more metallic and similar to the description of graphite, which can conduct electricity, but not diamond.

A 3D network lattice of carbon atoms held together by hydrogen bonding and dispersion forces. Hydrogen bonding and dispersion forces are intermolecular forces, although dispersion forces are everywhere, but very weak.

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Correct Answer: C. nuclear decay

Nuclear decay involves the splitting of an unstable nucleus and emitting a radioactive particle. This process also decreases the energy of the original element. Nucleation though a chemistry term is related to the process of making a crystal from a supersaturated solution. A combustion reaction does generally result in the release of energy, but is not a mechanism used to make a nucleus more stable. Nuclear fusion is the process of adding elements together, increasing their energy, not decreasing their energy.

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