DAT Question of the Day

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. The gas is under low pressure and high temperature.

An ideal gas is a gas which obeys the Ideal Gas Laws. Real gases behave ideally when their particles are moving at high speed (high temperature)and there is lots of space between the particles (low pressure).The lower the temperature and higher the pressure the less ideal the gas behaves, especially as it approaches its liquidation point.

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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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Correct Answer: E. alpha particles

In order of increasing penetration power, alpha particles have the lowest, then beta particles, then gamma rays. Protons are not known to have penetrating power and a positron is generally unstable and quickly decomposes, so its penetrating power is considered to be negligible.

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Correct Answer: B. Mixture A would have a lower boiling point

The two mixtures have the same concentration a.k.a. molality. However, they do have differing ionic solutes. Mixture A has an ionic solute that would dissociate to form two ions (K⁺ and Cl^–) whereas Mixture B has an ionic solute that forms three ions (Mg2⁺ and 2Cl^–). In the equation:

∆T(boiling) = m x Kb x i, the “I” or vant Hoff factor would be the only variable. The higher the vant Hoff factor, the greater the effect on the boiling point and/or freezing point. The von hoff factor for Mixture A is 2, but for Mixture B is 3. Therefore, Mixture B would have the greater affect on the boiling point, making it higher than normal. Between the two mixtures, B would have a higher boiling point than mixture A.

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Correct Answer: C. Benzene, C6H6.

The law of solubility is that “Like dissolves Like”, that is non-polar solvents dissolve non-polar substances and polar solvents dissolve polar and most ionic substances.

Water is a polar solvent thus:

Salt, NaCl – ionic and very soluble in water, sea water.
Ethanol, CH3CH2OH – polar molecular (-OH) will dissolve in water, beer/wine/spirits.
Benzene, C6H6 – non-polar molecular will not dissolve in polar water.
Hydrogen chloride, HCl – polar molecular will dissolve in water, hydrochloric acid.
Acetic acid, CH3COOH – polar molecular (-COOH) will dissolve in water, vinegar.

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