AAMC Chem QPack-done

Question 1

thin layer chromatography on silica plates

Answer 1

more polar, lower Rf

Question 2

ph formula with pka

Answer 2

ph=pka+log([conj. base]/conj. acid])

Question 3

ionic bonds are most likely to form between elements of ___ and ____ electronegativity.

Answer 3

high and low

ex. Ca and i

Question 4

Alcohols generally require acid catalysis in order to undergo substitution by nucleophiles. The acid catalyst enhances the reaction by:

Answer 4

creating a better leaving group

This question asks the examinee to remember that the substitution reaction in question serves to replace the hydroxyl group and that hydroxide ion is one of the worst leaving groups in substitution reactions. Under acidic conditions, the hydroxyl group is protonated such that the leaving group is now water, a superior leaving group, rather than hydroxide ion. Thus, B is the best answer. Solvent polarity and basic impurities are not particularly relevant, and protecting the alcohol group defeats the purpose of the reaction.

Question 5

good nucleophiles are not ______ _____.

Answer 5

sterically hindered

Question 6

where are nonmetals on a period table

Answer 6

right

Question 7

pka and ka formula

Answer 7

pKa=-log Ka

Question 8

When the acid and conjugate base concentrations are equal, the pH of a buffer equals the ____ of the acid.

Answer 8

pKa

Question 9

Na2CO3 + HCl → CO2 + H2O + NaCl
Consider the above unbalanced equation. For this reaction, how many mL of a 2 M solution of Na2CO3 are required to produce 11.2 L of CO2 at STP?

Answer 9

250 mL

This question deals with stoichiometry, which examines the quantities of reactants and products associated with a chemical reaction. The first step in working stoichiometry problems is to balance the equation. For this reaction, the balanced equation is:

Na2CO3 (aq) + 2 HCl (aq) → CO2 (g) + H2O (l) + 2 NaCl (aq)
The problem seeks the volume of 2 M Na2CO3 solution which, when reacted with HCl solution, will produce 11.2 L of CO2 gas at STP (standard temperature and pressure). It is an important fact that one mole of an ideal gas, at STP, will occupy a volume of 22.4 L. Therefore, 11.2 L of CO2 gas, at STP, must represent 0.5 mole of CO2. (Virtually all gases can be approximated as ideal gases at common temperatures and pressures.) According to the balanced chemical equation, one mole of CO2 is produced when one mole of Na2CO3 reacts. Therefore, the amount of Na2CO3 required to produce 0.5 mole of CO2 gas must also be 0.5 moles. We must find the volume of 2 M Na2CO3 solution which contains the required 0.5 moles of reactant:

Question 10

1 mole of ideal gas at STP will occupy a volume of ___.

Answer 10

22.4L

Question 11

What are the oxidizing and reducing agents, respectively, in the reaction below?

2HCl + H2O2 + MnO2 → O2 + MnCl2 + 2H2O

Answer 11

MnO2; H2O2

In the reaction pictured, Mn is reduced from +4 to +2; therefore, MnO2 is the oxidizing agent. O is oxidized from -1 in H2O2 to 0 in O2; therefore, H2O2 is the reducing agent.

Question 12

Fatty acid general formula

Answer 12

A fatty acid would have the general formula Rn—CO2H

Question 13

The energy required to remove an electron from an atom is the ______ ____.

Answer 13

ionization potential

Question 14

Ionization constant

Answer 14

H2S was described as being a weak acid. This means that a small fraction of the solute molecule ionize and release protons into solution. The value of the ionization constant is therefore somewhere between 0 and 1, but much closer to 0. As an example, phosphoric acid, among the strongest of the weak acids, has an ionization constant that is approximately 1 x 10^-2, or 0.01. This is much closer to 0 than 1.

Question 15

phase diagram

Answer 15

solid is left, liquid is right, gas is bottom

Question 16

A sparingly soluble metal hydroxide, M(OH)2 has a molar solubility of S mol/L at 25°C. Its Ksp value is:

Answer 16

4S^3

The Ksp for a substance, AaBb, equals [A]a[B]b. The Ksp for M(OH)2 = [M][OH–]2. If the solubility of M(OH)2 is S mol/L, then [M] = S mol/L and [OH–] = 2S mol/L. The Ksp = S(2S)2 = S(4S2) = 4S3. Thus, D is the best answer.

Question 17

Suppose that CH4(g) reacts completely with O2(g) to form CO2(g) and H2O(g) with a total pressure of 1.2 torr. What is the partial pressure of H2O(g)?

Answer 17

0.8 torr

The balanced equation for the complete combustion of CH4(g) is shown below.

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

The pressure of the gaseous products is 1.2 torr. For every three product molecules, two are water. Therefore, the partial pressure of water is 2/3 the total pressure, because the total pressure is a function of the total number but not kind of molecules. Two-thirds of 1.2 torr is 0.8 torr. Thus, answer choice C is the best answer.

Question 18

Suppose that CH4(g) reacts completely with O2(g) to form CO2(g) and H2O(g) with a total pressure of 1.2 torr. What is the partial pressure of H2O(g)?

Answer 18

0.8 torr

The balanced equation for the complete combustion of CH4(g) is shown below.

CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

The pressure of the gaseous products is 1.2 torr. For every three product molecules, two are water. Therefore, the partial pressure of water is 2/3 the total pressure, because the total pressure is a function of the total number but not kind of molecules. Two-thirds of 1.2 torr is 0.8 torr. Thus, answer choice C is the best answer.

Question 19

lower Ksp means

Answer 19

lower solubility and lower concentrations of the cation and anion

Question 20

catalysts…

Answer 20

catalysts lower the activation energy of the slowest step in a reaction. Thus, they increase the rate of the reaction without increasing the number of collisions, the kinetic energy of the reactants, or the Keq of a reversible reaction.

Question 21

ideal gas

Answer 21

It is assumed that the molecules in an ideal gas have no volume and that there are no interactions between the molecules.

Question 22

electrolytic vs galvanic cells

Answer 22

learn :)