DAT Question of the Day

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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Correct Answer: D. C8H32

To determine the molecular formula using an empirical formula, the ratio of the molecular mass to the empirical mass must be calculated. Dividing the molecular mass of 128 grams by the empirical mass of ~16 grams (C = 12g + H = 1g, but there are 4 hydrogens in the compound) gives you approximately 8. This indicates that the empirical subscripts must be multiplied by 8 to result in the molecular formula of the unknown compound, C8H32.

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Correct Answer: C. 0

In the equation, carbon is used from carbon dioxide to form glucose, C6H12O6. The final form of carbon is in glucose. In this compound, the oxygens each have an oxidation number of -2 and the hydrogen also have a fixed oxidation number of +1 each. Therefore, the sum of hydrogen’s oxidation numbers is +12 and the sum of oxygen’s oxidation numbers is -12. Since glucose is a neutral compound the sum of all the oxidation numbers of all the elements in the compound must be equal to zero. So, carbon must have an oxidation number of 0 because the sum of the hydrogen and oxygen oxidation numbers is already equal to zero.

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Correct Answer: E. C22H46

The answer options are all nonpolar compounds. Non-polar compounds have only London dispersion as their intermolecular force, which is relatively weak in comparison to the other intermolecular forces. However, the strength of London Dispersion increases with higher molecular mass. Therefore, the compound with the highest boiling point would be the compound with the strongest intermolecular force, which in this case is only London dispersion. Answer option [E] would have the highest boiling point of the answer options as it has the highest molecular mass.

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Correct Answer: D. 22.4

The ideal gas law, PV = nRT when divided by P results in: (nRT) / P = V, assuming that there is 1 mol at STP, this would equal 22.4L, which is also known as the molar volume of an ideal gas.

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Correct Answer: E. 2, 13, 10, 8

This question requires that you remember the formula for butane and how to create a combustion reaction. First, you have to know that butane has 4 carbons. Then you can use the (2×n)+2 rule to find the number of hydrogens – in this case 10 hydrogens. To remember the amount of carbons in the major hydrocarbons, use the mnemonic “Men Eat Peanut Butter”, or “methane (1 carbon), ethane (2 carbons), propane (3 carbons), butane (4 carbons)”.

The following equation is needed for this question:

C4H10 + O2 -> H2O + CO2

To balance this equation, a 2 should be placed in front of C4H10 to make it easier to balance.
2 C4H10 + O2 -> H2O + CO2

Next, an 8 must be placed on the right side in front of CO2 to balance the carbons.
2 C4H10 + O2 -> H2O + 8 CO2

Next, a 10 must be placed on the right side, in front of H2O to balance the hydrogens.
2 C4H10 + O2 -> 10 H2O + 8 CO2

Finally, a 13 must be placed on the left side, in front of O2 to balance oxygen.
2 C4H10 + 13 O2 -> 10 H2O + 8 CO2

Thus, the coefficients needed to balance this equation are: 2, 13, 10, 8, or answer option [E].

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