DAT Question of the Day

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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Correct Answer: D. +4

This is an example of an ionic compound. For every 1 iron atom, 2 sulfate ions are needed. If sulfate has a charge of -2 and 2 sulfates are present, then this results in a charge of -4. Since the ionic compound in the question is neutral, there should not be a charge left on the compound. Therefore, if sulfate has a -4 (is looking to gain 4 electrons), then the iron must have a +4 charge (be willing to transfer 4 electrons).

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Correct Answer: E. the C-N bond is shorter because it is a triple bond.

The bond length depends on the type of bond. Single bonds are longer than double bonds, which are longer than triple bonds. Drawing the Lewis dot diagrams for these compounds gives some insight into the type of bonds formed between C and N and C and H. The C-N bond is shorter as it is a triple bond. The C-H bond would be longer since it is a single bond. The magnitude of the difference cannot be calculated based on the limited information in the question, but at least the relative sizes of the bonds can still be determined.

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Correct Answer: A. Linear

Cyanide is CN^-1 and this compound has 10 valence electrons to use to bind together. The only orientation that works with these elements is with a triple bond between the C and N, with each element having a single pair of non-bonded electrons. This would give rise to a linear molecular geometry.

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Correct Answer: C. 11.2 L

This is solved using the ideal gas law. However, it should be recognized that 1 mol of any gas at 1 atm and 273K (or 0 deg Celsius) is approximately 22.4 L in volume. If this is not recognized, it can still be calculated from the ideal gas law, PV = nRT. We recognize that if pressure doubles while temperature and mols remain the same, the volume should be halved. Thus, the new volume is 11.2 L, which is a difference of 11.2 liters, or answer C.

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Correct Answer: E. (45.1 grams)/(0.65(.302)moles)

To determine the molar mass, the molarity equation will be needed.

Molarity = (moles of solute)/(Liters of solution)

Plugging in the values from the problem results in:

0.65 = (moles of solute)/(.302 L)

Note: The amount of the solution is given in terms of grams of water, this can be converted to mL by using the density of water (1.0 grams/mL) and then converting the mL into liters. Cross-multiplying gives the following:

0.65(.302) = moles of solute

The molar mass of a compound is in grams per mole. Therefore the molar mass of the unknown solute would be 45.1 grams of solute (from the question) divided by the number of moles just calculated 0.65(.302). Putting the pieces together results in a molar mass of the unknown solute of:

(45.1 grams)/0.65(.302)moles

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