DAT Question of the Day

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: 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. 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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Correct Answer: D. the kinetic energy of the gas particles would decrease

If the balloon is placed in the freezer, the particles lose kinetic energy as the gas particles slow down and have fewer collisions with each other and the container. As a result, if the internal collisions between the gas particles and the inside of the balloon decrease, the volume of the balloon would also decrease and eventually the balloon would deflate. This is a prime example of Charles’ Law.

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Correct Answer: D. average kinetic energy quadruples.

The temperature (in Kelvins) of a gas is directly proportional to the average kinetic energy of the gas. Therefore, if the temperature is quadrupled, so to is the average kinetic energy of the gas.

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Correct Answer: D. it increases, then becomes constant.

A pressure cooker fixes the atmospheric pressure to be higher than normal. In order for a liquid to boil, the vapor pressure inside of the container must be at least equal to the atmospheric pressure. For higher atmospheric pressures, like in a pressure cooker, the vapor pressure must also increase. Therefore, it takes longer for the vapor pressure of the gas to accumulate, leaving the liquid to become hotter and hotter. Once the boiling point is reached, the liquid is hotter than normal, cooking the food faster. Once the vapor pressure equals the environmental pressure of the pressure cooker, it remains constant. At this point the liquid is boiling and the vapor pressure of the liquid is equal to the atmospheric pressure of the pressure cooker. In this case, the only answer option that aligns correctly to what occurs in a pressure cooker is [D].

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Correct Answer: C. A pointer on a meter or surface of a liquid in a buret or pipette is not observed from directly straight on.

All options are common laboratory errors, but Parallax Error may occur when a pointer on a meter or surface of a liquid in a buret or pipette is not observed from directly straight on. If they are observed from above or below then the liquid surface or pointer will not be seen to line up with the scale.

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Correct Answer: A. High entropy, exothermic reactions with a low activation energy.

TNT explosions are very fast reactions (the lower the activation energy the less a reaction is impeded) involving the production of enormous quantities of heat (exothermic) and gaseous products (the production of hot gases from a solid explosive dramatically increases the disorder of the system, thus high entropy).

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