DAT BOOTCAMP QUESTIONS Flashcards
Effects of positron emission, electron capture, alpha decay, and beta decay
Positron emission (β+ decay) = Proton -> Neutron
Electron capture = Proton + Electron -> Neutron
Alpha Decay (α-decay) = Emits a Helium atom. Reduces mass number.
Beta Decay (β– decay) = Neutron -> Proton + Electron emitted
Describe why the answer for this question is positive (C).
The ∆Hf for Br(g) is +193 kJ/mol. What is the bond dissociation energy of a Br-Br bond? A. +193 kJ / mol B. -193 kJ / mol C. +386 kJ / mol D. -386 kJ / mol E. +96.5 kJ / mol
Bond dissociation energies are always positive because we have to put in energy to break the bond.
In other words, the bond has to absorb energy, meaning bond breaking is an endothermic process
Element X has a nucleus that is stable against decomposition. Which of the following must be true of Element X?
A. the effective nuclear charge is high
B. the nuclear binding energy is high
C. the ionization energy is high
D. the electron shielding effect is high
E. the bond dissociation energy is high
B
Binding energy is the energy needed to split the nucleus into the individual components, i.e. protons and neutrons (or nucleons). The higher the binding energy, the harder it is to decompose the nucleus.
The effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. It explains the atomic radii trend across periods.
The electron shielding effect dictates the atomic radii trend down a group.
Bond dissociation energy deals with compounds, not nuclei.
Which of the following is true for the energy diagram of a reversible exothermic reaction?
A. The forward reaction proceeds slower than the reverse reaction.
B. The enthalpy of the products is greater than the enthalpy of the reactants.
C. The reverse reaction has a higher activation energy than the forward reaction.
D. The reverse reaction has a lower activation energy than the forward reaction.
E. The forward reaction has a higher activation energy than the reverse reaction.
C
know what exo vs endothermic reaction diagrams look like
Explain why HI is a stronger acid than HBr.
The strength of an acid is usually determined by how much the acid _____.
Thus, the ____ the bond holding the proton to the molecule, the ____ the acid is.
disassociates, weaker, stronger
The bond strength is largely determined by the difference in electronegativity.
Fluorine is one of the most electronegative elements, and thus is not as strong of an acid as HCl or HI, which have weaker bonds, and thus a more readily available proton.
If given the Kc of the forward reaction, how would you find the Kc of the reverse?
reverse is the reciprocal!
Raoult’s Law
PA = XaPpure
Ppure = vapor pressure of given compound
Xa = percentage of solvent in the solution
use this formula to find a new vapor pressure
Haber Process
Nitrogen and hydrogen react to form ammonia
What is the maximum number of electrons that can be held in the 4th energy level?
A. 2 B. 8 C. 10 D. 14 E. 32
E
The fourth energy level has four orbitals, s, p, d, and f.
S = 2 electrons
p = 6 electrons
d orbitals = 10 electrons
f orbitals = 14 electrons
Therefore the 4th energy level can hold at most 2 + 6 + 10 + 14 = 32 electrons. Notice that the first energy level can only hold 2 electrons. This is why helium is considered a noble gas even though it only has 2 electrons; it has a full energy level already!
The addition of a strong acid to a saturated solution of Mg(OH)2 that has 100g of solid remaining would cause which of the following?
a) increase pH
b) increase number of Mg ions in solution
c) increase number of OH ions in solution
B
The correct answer is [D]. Notice that Mg(OH)2 is technically insoluble, however, this does not mean that none of the reactant will dissolve. A very small portion of the Mg(OH)2 still dissolves according to the following reaction:
Mg(OH)2 ⇌ Mg2+ + 2OH–
The solution is saturated, meaning all the Mg(OH)2 that can dissolve has dissolved, and there are still 100g of it left as a solid. If we add a strong acid, or essentially H+, it will combine with the OH– to form H2O. Since some of the OH– has been removed, then according to Le Chatelier’s principle, the reaction will shift to the right to restore equilibrium. As a result, more Mg(OH)2 will be dissolved, and more Mg2+ will be released, or answer choice [D].
Given an elementary reaction, how would you find the:
- intermediate
- rate law
- overall reaction
- the intermediate will be made in the middle of the reaction and get used up before the end
- to find the rate law, it’s simply the reactants of the SLOW STEP
- overall will be adding up elementary steps and cancelling the intermediates out
An exothermic reaction at equilibrium will proceed at a:
A. slower rate while its Kc increases at higher temperatures.
B. slower rate while its Kc decreases at higher temperatures.
C. faster rate while its Kc increases at higher temperatures.
D. faster rate while its Kc decreases at higher temperatures.
D
*think of this one mathematically
From Le Chatlier’s principle, increasing the temperature would increase the heat, so therefore the reaction would shift to the left (towards the reactants, [A] and [B]).
If the concentrations of [A] and [B] increase, then the overall Kc of the reaction would decrease at higher temperatures, eliminating answer choices A and C.
Lastly, increasing the temperature will increase the rates of both the forward and the reverse reactions, so the reaction will proceed at a faster rate. Thus we arrive at answer choice D.
Metal oxides produce ___ solutions in water.
Non-metal oxides produce ___ solutions in water.
basic, acidic
give examples of both!
A solid compound that has a vapor pressure higher than atmospheric pressure will most likely be able to do which of the following?
A. melt B. freeze C. condense D. vaporize E. sublime
E
If a solid compound has a high internal vapor pressure relative to the external environment, the compound will be able to sublime as the particles will be able to readily turn into vapor without first transitioning into the liquid state. This is seen with dry ice, as the dry ice has a higher vapor pressure than the atmosphere, thus as the dry ice “evaporates” the solid particles are said to sublime.
If the conjugate base of a molecule has a pKb of 1.4, what would you expect the molecule to be?
a) strong acid
b) weak acid
C) neutral
D) weak base
E) strong base
B
- Strong acids have a weak conjugate base.
- Strong bases have a weak conjugate acid.
So if the problem says you have a strong conjugate base, then the molecule must be a weak acid. To illustrate this, think of ammonium, NH4+. Ammonium is a weak acid, but the conjugate base of ammonium is ammonia, NH3, which is a reasonably good base. Thus, the correct answer is [B].
Electron affinity measures the:
A. tendency to attract electrons towards the atom and form a bond.
B. chemical reactivity of the valence electrons of the atom.
C. amount of energy absorbed when an electron is added to an atom.
D. ease with which an atom gains an electron.
E. average distance between the electrons and nucleus.
D
Normal Boiling Point
The temperature at which the vapor pressure of the liquid equals one atmosphere of pressure.
Water molecules in an aqueous solution will have the strongest interactions with ions with which of the following characteristics?
A. Small charge and small size
B. Small charge and large size
C. Large charge and small size
D. Large charge and large size
C
Let’s first examine charge. A polar water molecule will be more likely to interact with an ion with more charge. This is a stretch of the analogy “like dissolves like”. The high polarity molecule will enjoy the company of a highly charged ion, and this will result in a greater interaction between the two.
For size, think about the charged ion and water molecule as two tiny magnets. When these magnets are spaced far apart, they barely have an effect on each other. As you bring the magnets closer together, you begin to feel their force of interaction. The same principle applies to a water molecule and a charged ion in an aqueous solution. We need to minimize the distance between the water molecule and charged ion, and we can do that by choosing an ion with a smaller size.
A student finds that the average number of cells over 10 samples is 2130, with a standard deviation of ±6. However, the professor determines the true average number of cells is 2850. The student’s measurement was:
A. inaccurate and precise
B. accurate and imprecise
C. inaccurate and imprecise
D. accurate and precise
The definition of accuracy is that the measurement taken is close to the true value, whereas the definition of precise is that the measurement produces consistent results.
Thus, the student’s measurements were precise, since we can see the standard deviation is LOW compared to the total number of cells, meaning the variation of each measurement was low.
However, the measurement was inaccurate, because the measured value by the student differed significantly from the true value.
What is the molar solubility of BaF2 (Ksp = 1.8×10-7) in 0.10 M sodium fluoride?
A. 1.8×10-5 M B. 1.8×10-7 M C. 1.8×10-9 M D. (1.8×10-7)1/2 M E. (1.8×10-7)2 M
A
BaF2(s) Ba2+(aq) + 2F–(aq)
Ksp = [Ba2+][F–]2
We can solve this via an ICE table, which is the longer way, or we can skip to the end and just use the Ksp equation above to solve the question. Speed is important on the DAT, so we’re going to solve this the fast way.
Let x = molar solubility of BaF2
We have 1 ion of Ba2+ and 2 ions of F–. We’re going to assume that the molar solubility of BaF2 is very small (common on the DAT since we don’t have a calculator) and that it probably won’t impact the concentration of fluoride that much. Therefore:
Ksp = [Ba2+][F–]2
Ksp = 1.8×10-7 = (x)(0.10)2
Solve for x, the molar solubility
A researcher has a solution of 3M nitric acid that she needs to neutralize. In order to do this, she decides to add the acid to a solution to neutralize it. Which of the following would neutralize the acid the fastest?
A. Br- B. Na3PO4 C. NH3 D. Cl- E. H2O
B
In order to neutralize the acid the fastest, we want the base that is capable of absorbing the most protons per molecule.
Na3PO4 is able to absorb 3 protons, because it dissociates into the very basic PO43- ion. Thus, adding trisodium phosphate would neutralize the acid the fastest, versus the other answer choices that would only absorb 1 proton.
Strategy tip: We could eliminate Br– and Cl– immediately because they’re both almost identical (weak base, halide). Given that there cannot be two correct answers, both of them must be wrong.
