MCAT C/P, B/S and P/S Exam Review
Questions and Answers
Increases the ability of the solution to conduct electricity b/c solns containing dissolved
salts release charged particles into solution that can carry an electric current -
ANSWER-Increasing the molarity of an ionic solution
1.5:0.5:1
Q is asking which ratio of PBS by mass would make a solution of the greatest molarity.
Na2HPO4 doesn't dissociate so can be disregarded in comparing molarities.
For any equal mass of each salt, NaCl will always provide more moles. Q boils down to
which of these mixtures has more NaCl present.
PBS already has a set mass of Nacl, KCl and Na2HPO4 so the mass ratio is of mass of
each salt compared to the total mass of PBS. NaCl will always produce more moles
when its molar mass is multiplied by an equal mass. - ANSWER-The highest measured
current at a given voltage during the exp. would most likely be produced by pBS with
which mass ratio of NaCl, KCl and Na2HPO4?
A charge carrier is a particle that is free to move, carrying an electric charge, esp. the
particles that carry electric charges in electrical conductors. Charge carriers are different
from electron transporters. - ANSWER-What are charge carriers in electric circuits?
NaCH3COO almost completely ionizes, providing more charge carriers in the soln.
Increasing the number of charge carriers in the soln causes an increased amplitude in
the current reading. - ANSWER-After adding the sodium acetate soln, an increased
amplitude in the current reading was observed. Which of the following best explains this
phenomenon?
Propanol.
Whole point of using ethanol is to precipitate DNA b/c the added sodium acetate
introduces Na+ ions that interact with DNA's negatively charged phosphate backbone,
leaving the DNA too polar to remain soluble in the substantially less polar ethanol soln.
Ethanol is miscible with water and won't form two phases. Its addition serves to reduce
the polarity of the solution.
So we need a molecule that's miscible with water but also non-polar enough to
precipitate DNA. Propanol is most similar to ethanol - ANSWER-If the lab ran out of
ethanol, which of the following chemicals would be most appropriate to use for the
precipitation procedure?
Yes, nitrogen would behave differently b/c of the already high quantities of nitrogen in
the air. Nitrogen makes up the largest proportion of the gases in the air of around 75%.
, Releasing 6000 ppm of nitrogen into a room would not detectably increase the partial
pressure of nitrogen. There would then be less of a concentration gradient for nitrogen
to diffuse down so the concentration would simply remain constant. The other gases
listed would display the same behavior of diffusing out of the room. - ANSWER-If the
exp in Figure 1 was repeated with N2, would it give a different result than having used
CO2?
Amides in alkaline conditions would undergo hydrolysis to form ammonia and the salt of
the corresponding acid, the ethanoic acid. The ammonia gas would then bubble out of
the liquid solution. Ammonium ion would be produced only if the amide were hydrolyzed
in acidic conditions. Physically write out the eq. if the question gives you a reaction. -
ANSWER-Ethanamide undergoes hydrolysis in a test tube containing a solution with a
pH of 11. Which of the following describes what would happen if a strip of moist litmus
paper was held above the test tube?
- favors the side of the equilibrium with fewer moles of gas b/c the pressure will increase
- ANSWER-Effect of decreasing the volume of the system
- removing a reactant b/c heat in a rxn with positive enthalpy means that heat is on the
reactant side - ANSWER-What would decreasing the temp. of a rxn with positive
enthalpy mean?
For data that isn't skewed: a small sample size normally < 10 is sufficient
For data that is moderately skewed: n>=25 (central limit theorem) and may need an
even larger sample size if the data is highly skewed - ANSWER-What is considered a
small sample size?
Intramolecular forces (NOT intermolecular forces) influence acid strength
1) Acid strength increases as the EN of the nonmetal atom increases
- polarity of a X-H bond increases with the EN of the nonmetal atom b/c it withdraws
more electrons away from the hydrogen atom
2) Acid strength increases as the atomic radius of the non-metal atom increases
- strength of the X-H bond decreases as the atomic radius of X increases
- H+ is more easily broken away from a larger atom than a smaller one b/c the e- cloud
in a large atom is more diffuse (smaller the non-metal atom, the more dense the e-
cloud)
*When comparing acid strengths of hydrides in a group of the periodic table, the acid
strength increases with increasing atomic radius of the nonmetal. When reading across
a row of the periodic table, the importance of bond polarity outweighs that of atomic
radius.*
3) Resonance structure increases acidity - ANSWER-Factors that affect acid strength
Reactivity: relates to concepts of chemical stability and chemical compatibility
Mechanism: ways in which substances interact with membranes, for example to affect
their stability (ex. passage said "either the flavonoids bind at the lipid-water interface or
they distribute themselves in the hydrophobic core of the membrane" - indicating
Questions and Answers
Increases the ability of the solution to conduct electricity b/c solns containing dissolved
salts release charged particles into solution that can carry an electric current -
ANSWER-Increasing the molarity of an ionic solution
1.5:0.5:1
Q is asking which ratio of PBS by mass would make a solution of the greatest molarity.
Na2HPO4 doesn't dissociate so can be disregarded in comparing molarities.
For any equal mass of each salt, NaCl will always provide more moles. Q boils down to
which of these mixtures has more NaCl present.
PBS already has a set mass of Nacl, KCl and Na2HPO4 so the mass ratio is of mass of
each salt compared to the total mass of PBS. NaCl will always produce more moles
when its molar mass is multiplied by an equal mass. - ANSWER-The highest measured
current at a given voltage during the exp. would most likely be produced by pBS with
which mass ratio of NaCl, KCl and Na2HPO4?
A charge carrier is a particle that is free to move, carrying an electric charge, esp. the
particles that carry electric charges in electrical conductors. Charge carriers are different
from electron transporters. - ANSWER-What are charge carriers in electric circuits?
NaCH3COO almost completely ionizes, providing more charge carriers in the soln.
Increasing the number of charge carriers in the soln causes an increased amplitude in
the current reading. - ANSWER-After adding the sodium acetate soln, an increased
amplitude in the current reading was observed. Which of the following best explains this
phenomenon?
Propanol.
Whole point of using ethanol is to precipitate DNA b/c the added sodium acetate
introduces Na+ ions that interact with DNA's negatively charged phosphate backbone,
leaving the DNA too polar to remain soluble in the substantially less polar ethanol soln.
Ethanol is miscible with water and won't form two phases. Its addition serves to reduce
the polarity of the solution.
So we need a molecule that's miscible with water but also non-polar enough to
precipitate DNA. Propanol is most similar to ethanol - ANSWER-If the lab ran out of
ethanol, which of the following chemicals would be most appropriate to use for the
precipitation procedure?
Yes, nitrogen would behave differently b/c of the already high quantities of nitrogen in
the air. Nitrogen makes up the largest proportion of the gases in the air of around 75%.
, Releasing 6000 ppm of nitrogen into a room would not detectably increase the partial
pressure of nitrogen. There would then be less of a concentration gradient for nitrogen
to diffuse down so the concentration would simply remain constant. The other gases
listed would display the same behavior of diffusing out of the room. - ANSWER-If the
exp in Figure 1 was repeated with N2, would it give a different result than having used
CO2?
Amides in alkaline conditions would undergo hydrolysis to form ammonia and the salt of
the corresponding acid, the ethanoic acid. The ammonia gas would then bubble out of
the liquid solution. Ammonium ion would be produced only if the amide were hydrolyzed
in acidic conditions. Physically write out the eq. if the question gives you a reaction. -
ANSWER-Ethanamide undergoes hydrolysis in a test tube containing a solution with a
pH of 11. Which of the following describes what would happen if a strip of moist litmus
paper was held above the test tube?
- favors the side of the equilibrium with fewer moles of gas b/c the pressure will increase
- ANSWER-Effect of decreasing the volume of the system
- removing a reactant b/c heat in a rxn with positive enthalpy means that heat is on the
reactant side - ANSWER-What would decreasing the temp. of a rxn with positive
enthalpy mean?
For data that isn't skewed: a small sample size normally < 10 is sufficient
For data that is moderately skewed: n>=25 (central limit theorem) and may need an
even larger sample size if the data is highly skewed - ANSWER-What is considered a
small sample size?
Intramolecular forces (NOT intermolecular forces) influence acid strength
1) Acid strength increases as the EN of the nonmetal atom increases
- polarity of a X-H bond increases with the EN of the nonmetal atom b/c it withdraws
more electrons away from the hydrogen atom
2) Acid strength increases as the atomic radius of the non-metal atom increases
- strength of the X-H bond decreases as the atomic radius of X increases
- H+ is more easily broken away from a larger atom than a smaller one b/c the e- cloud
in a large atom is more diffuse (smaller the non-metal atom, the more dense the e-
cloud)
*When comparing acid strengths of hydrides in a group of the periodic table, the acid
strength increases with increasing atomic radius of the nonmetal. When reading across
a row of the periodic table, the importance of bond polarity outweighs that of atomic
radius.*
3) Resonance structure increases acidity - ANSWER-Factors that affect acid strength
Reactivity: relates to concepts of chemical stability and chemical compatibility
Mechanism: ways in which substances interact with membranes, for example to affect
their stability (ex. passage said "either the flavonoids bind at the lipid-water interface or
they distribute themselves in the hydrophobic core of the membrane" - indicating
