MCAT Test 16 with Accurate Solutions
Mercury has a greater density than water, so what can we say about the buoyant force
and the force of surface tension? - ANS-The buoyant force and surface tension are both
greater in Mercury
What explains why a water droplet forms a roughly spherical shape if not acted upon by
external forces? - ANS-A sphere minimizes the surface area of the shape for a given
volume, which yields the lowest-energy state for the molecules.
Units of surface tension coefficient - ANS-
What would happen if an aluminum coin (ρ = 2700 kg/m3, L = 1 cm, V = 1 × 10-8 m3)
were gently placed on the surface of water? - ANS--The force of surface tension by
itself would be sufficient to make the coin float.
-The maximum buoyant force for the coin is given by Fb = ρfVsubg, which for the given
situation is Fb = (1000)(10-8)(10) = 10-4 N. The weight of the coin is w = mg = ρcoinVg
= (2700)(10-8)(10) = 2.7 × 10-4 N. The weight is greater than the buoyant force, so
eliminate choice A: the buoyant force alone is not good enough. The maximum force of
surface tension is Fst,y = γL (twice, because the passage says that there are two of
them). This comes out to Ftotal surface tension = (2)(0.07)(0.01) = 1.4 × 10-3 N. That's
greater than the weight, so the surface tension alone can balance the weight and allow
the coin to float.
What explains why F2 is higher than Cl2 in the reactivity series? (what makes F2 more
reactive than Cl2) - ANS--F2 has a more negative Δ(SE)° than Cl2
-if the Δ(SE)° is more negative for F2, the overall ΔG° is more negative indicating it is
more energetically favorable to add an electron to F2 compared to Cl2.
What best explains the observed difference in electron affinity between chlorine and
fluorine? - ANS-Fluorine has a smaller atomic volume than chlorine, resulting in
stronger repulsive forces between the existing electrons and the electron being added
The smaller atomic volume leads to greater repulsive forces between the existing
electrons and the electron being added
A medium with index of refraction n is surrounded by air. The critical angle inside of the
medium is then determined. The medium is then submerged in a fluid with index of
refraction nfluid. If 1 < nfluid < n how is the critical angle affected? - ANS--It is measured
inside of the medium and is greater than its previous value
-Total internal reflection can only happen when the incident medium has a greater index
of refraction than the surrounding medium. Since the original medium has a greater
index of refraction than the fluid, it must still be the incident medium.
,-Snell's law of refraction states that n1sinθ1 = n2sinθ2. For total internal reflection, θ1 =
θcritical and θ2 = 90°, which means that n1sinθcritical = n2. The index of refraction of
air (n2 in this case) is 1, so immersing the medium in fluid has caused n2 to increase.
Since n1 remains constant, the equation tells us that sinθcritical, and therefore θcritical
itself, must increase.
The more negative the H0 of a superacid is means what? - ANS-The more negative, the
stronger the acid
What are the three major ways in which antibiotics interact with bacteria? - ANS--
Membrane protein solubilization
-Leakage of cytosolic content
-Detergent fro the cell membrane
If a substrate has a positive charge on it, what kind of amino acid would most likely be in
the active site? - ANS--One with a positive charge like aspartic or glutamic acid- positive
charge means negatively acidic amino acids and vice versa
Why is CH3F unlikely to methylate something? - ANS--Fluorine is a very unlikely leaving
group, so it is unlikely to leave the -CH3 group that it is bonded to
Can KHSO4 and NH4Cl lower the pH of a solution? - ANS-Yes, they will
The conjugate acid of a weak base will lower the pH, while the conjugate base of a
weak acid will raise it. Conjugates of strong acids or bases have no effect on pH. NH4+,
the conjugate of the weak base NH3, is acidic.
K+ and HSO4- are conjugates of a strong base and strong acid, respectively. Generally
this would indicate a neutral salt. However, the HSO4- ion is acidic in its own right and
will lower the pH
Carnitine deficiency is an example of a medical condition affecting the metabolism of
fatty acids. Which of the following would you expect to see in the cells of an individual
with this condition? - ANS-Accumulation of fatty acids in the cytosol and decreased β-
oxidation activity
Carnitine allows transport of fatty acids from the cytosol into the mitochondria. The lack
of carnitine would mean that cells would accumulate fatty acids in the cytosol.
β-oxidation occurs inside the mitochondrial matrix. If fatty acids cannot enter the
mitochondria, β-oxidation activity would decrease
Release of which of the following peptides will increase the activity of β-oxidation? -
ANS-Glucagon and epinephrine
Why is radon not used fro smoke alarms? - ANS-Its decay releases hazardous gases
In a fluorescence units/ sec mg protein vs [Cation] graph, what can you conclude about
a transporter if one ion levels off and the other continues to increase on the graph? -
, ANS--If one levels off, than we can conclude that the transporter has a greater affinity
fro it than the other ion
What does a mixed inhibitor do? - ANS-A mixed inhibitor will always decrease the Vmax
but the Km can either increase or decrease
Protein folding involves both the formation of secondary and tertiary protein structure to
ultimately generate a stereotyped final configuration. What is true of the folding
process? - ANS--The Gfolded is smaller than Gunfolded
-Secondary and tertiary protein structure largely depends upon the formation of weak
interactions including both hydrogen bonding and Van der Waals forces. Formation of
these interactions will release energy resulting in a negative ΔH
-The folding process occurs spontaneously in order to reach an energy minimum and
having multiple potential final folded products would likely not result in a functional
protein
-Burial of polar amino acids in what is most frequently a nonpolar interior would
significantly decrease the stability of the folded state
The standard reduction potentials (E°) of Cl2 and Na+ are 1.36 V and -2.71 V
respectively. What is the standard free energy change in the following reaction (F =
96,485 C/mol e-, 1 V = 1 J/C)?
Cl2 + 2Na -> 2NaCl - ANS--The solution requires the formula ΔG° = -nFE°. By summing
the voltages for the oxidation of Na (2.71 V) and the reduction of Cl2 (1.36 V) we arrive
at a total voltage change for the reaction of +4.07 V. Since E° is positive, the answer
must be negative
-Substitute +4.07 volts into the equation, using an approximate value of F ~ 10^5:
ΔG° = -(2)(105)(4) = -8 × 10^5 J.
A monochromatic beam used in DEI is composed of photons with an energy of 30 keV.
What is wavelength of the photons that reach the imaging screen after diffracting from
an analyzer angle of Δθ = 5 μrad? (Planck's constant h = 4.14 × 10-15 eV·s.) - ANS-The
relation between photon energy and wavelength is given by E = hc / λ, so λ = hc / E =
(4.14 × 10-15 eV·s × 3 × 108 m/s) / (30 × 103 eV) = 4.1 × 10-11 m.
The analyzer angle does not affect the energy of a given photon, but rather the number
of photons that reflect toward the screen (beam intensity being proportional to number
of photons)
A 42 year-old female presents with hemolytic anemia (inappropriate destruction of red
blood cells) secondary to a pyruvate kinase deficiency (the final enzyme in glycolysis).
What best describes the mechanism of her hemolytic anemia? - ANS--Inadequate ATP
resulting in failure of primary active transport and subsequent cell damage
-A deficiency in the final enzyme of glycolysis would significantly reduce ATP production
and in red blood cells, which lack mitochondria, glycolysis is the principal source of
ATP. Pumps relying on ATP, primary active transporters, would fail leading to cell
Mercury has a greater density than water, so what can we say about the buoyant force
and the force of surface tension? - ANS-The buoyant force and surface tension are both
greater in Mercury
What explains why a water droplet forms a roughly spherical shape if not acted upon by
external forces? - ANS-A sphere minimizes the surface area of the shape for a given
volume, which yields the lowest-energy state for the molecules.
Units of surface tension coefficient - ANS-
What would happen if an aluminum coin (ρ = 2700 kg/m3, L = 1 cm, V = 1 × 10-8 m3)
were gently placed on the surface of water? - ANS--The force of surface tension by
itself would be sufficient to make the coin float.
-The maximum buoyant force for the coin is given by Fb = ρfVsubg, which for the given
situation is Fb = (1000)(10-8)(10) = 10-4 N. The weight of the coin is w = mg = ρcoinVg
= (2700)(10-8)(10) = 2.7 × 10-4 N. The weight is greater than the buoyant force, so
eliminate choice A: the buoyant force alone is not good enough. The maximum force of
surface tension is Fst,y = γL (twice, because the passage says that there are two of
them). This comes out to Ftotal surface tension = (2)(0.07)(0.01) = 1.4 × 10-3 N. That's
greater than the weight, so the surface tension alone can balance the weight and allow
the coin to float.
What explains why F2 is higher than Cl2 in the reactivity series? (what makes F2 more
reactive than Cl2) - ANS--F2 has a more negative Δ(SE)° than Cl2
-if the Δ(SE)° is more negative for F2, the overall ΔG° is more negative indicating it is
more energetically favorable to add an electron to F2 compared to Cl2.
What best explains the observed difference in electron affinity between chlorine and
fluorine? - ANS-Fluorine has a smaller atomic volume than chlorine, resulting in
stronger repulsive forces between the existing electrons and the electron being added
The smaller atomic volume leads to greater repulsive forces between the existing
electrons and the electron being added
A medium with index of refraction n is surrounded by air. The critical angle inside of the
medium is then determined. The medium is then submerged in a fluid with index of
refraction nfluid. If 1 < nfluid < n how is the critical angle affected? - ANS--It is measured
inside of the medium and is greater than its previous value
-Total internal reflection can only happen when the incident medium has a greater index
of refraction than the surrounding medium. Since the original medium has a greater
index of refraction than the fluid, it must still be the incident medium.
,-Snell's law of refraction states that n1sinθ1 = n2sinθ2. For total internal reflection, θ1 =
θcritical and θ2 = 90°, which means that n1sinθcritical = n2. The index of refraction of
air (n2 in this case) is 1, so immersing the medium in fluid has caused n2 to increase.
Since n1 remains constant, the equation tells us that sinθcritical, and therefore θcritical
itself, must increase.
The more negative the H0 of a superacid is means what? - ANS-The more negative, the
stronger the acid
What are the three major ways in which antibiotics interact with bacteria? - ANS--
Membrane protein solubilization
-Leakage of cytosolic content
-Detergent fro the cell membrane
If a substrate has a positive charge on it, what kind of amino acid would most likely be in
the active site? - ANS--One with a positive charge like aspartic or glutamic acid- positive
charge means negatively acidic amino acids and vice versa
Why is CH3F unlikely to methylate something? - ANS--Fluorine is a very unlikely leaving
group, so it is unlikely to leave the -CH3 group that it is bonded to
Can KHSO4 and NH4Cl lower the pH of a solution? - ANS-Yes, they will
The conjugate acid of a weak base will lower the pH, while the conjugate base of a
weak acid will raise it. Conjugates of strong acids or bases have no effect on pH. NH4+,
the conjugate of the weak base NH3, is acidic.
K+ and HSO4- are conjugates of a strong base and strong acid, respectively. Generally
this would indicate a neutral salt. However, the HSO4- ion is acidic in its own right and
will lower the pH
Carnitine deficiency is an example of a medical condition affecting the metabolism of
fatty acids. Which of the following would you expect to see in the cells of an individual
with this condition? - ANS-Accumulation of fatty acids in the cytosol and decreased β-
oxidation activity
Carnitine allows transport of fatty acids from the cytosol into the mitochondria. The lack
of carnitine would mean that cells would accumulate fatty acids in the cytosol.
β-oxidation occurs inside the mitochondrial matrix. If fatty acids cannot enter the
mitochondria, β-oxidation activity would decrease
Release of which of the following peptides will increase the activity of β-oxidation? -
ANS-Glucagon and epinephrine
Why is radon not used fro smoke alarms? - ANS-Its decay releases hazardous gases
In a fluorescence units/ sec mg protein vs [Cation] graph, what can you conclude about
a transporter if one ion levels off and the other continues to increase on the graph? -
, ANS--If one levels off, than we can conclude that the transporter has a greater affinity
fro it than the other ion
What does a mixed inhibitor do? - ANS-A mixed inhibitor will always decrease the Vmax
but the Km can either increase or decrease
Protein folding involves both the formation of secondary and tertiary protein structure to
ultimately generate a stereotyped final configuration. What is true of the folding
process? - ANS--The Gfolded is smaller than Gunfolded
-Secondary and tertiary protein structure largely depends upon the formation of weak
interactions including both hydrogen bonding and Van der Waals forces. Formation of
these interactions will release energy resulting in a negative ΔH
-The folding process occurs spontaneously in order to reach an energy minimum and
having multiple potential final folded products would likely not result in a functional
protein
-Burial of polar amino acids in what is most frequently a nonpolar interior would
significantly decrease the stability of the folded state
The standard reduction potentials (E°) of Cl2 and Na+ are 1.36 V and -2.71 V
respectively. What is the standard free energy change in the following reaction (F =
96,485 C/mol e-, 1 V = 1 J/C)?
Cl2 + 2Na -> 2NaCl - ANS--The solution requires the formula ΔG° = -nFE°. By summing
the voltages for the oxidation of Na (2.71 V) and the reduction of Cl2 (1.36 V) we arrive
at a total voltage change for the reaction of +4.07 V. Since E° is positive, the answer
must be negative
-Substitute +4.07 volts into the equation, using an approximate value of F ~ 10^5:
ΔG° = -(2)(105)(4) = -8 × 10^5 J.
A monochromatic beam used in DEI is composed of photons with an energy of 30 keV.
What is wavelength of the photons that reach the imaging screen after diffracting from
an analyzer angle of Δθ = 5 μrad? (Planck's constant h = 4.14 × 10-15 eV·s.) - ANS-The
relation between photon energy and wavelength is given by E = hc / λ, so λ = hc / E =
(4.14 × 10-15 eV·s × 3 × 108 m/s) / (30 × 103 eV) = 4.1 × 10-11 m.
The analyzer angle does not affect the energy of a given photon, but rather the number
of photons that reflect toward the screen (beam intensity being proportional to number
of photons)
A 42 year-old female presents with hemolytic anemia (inappropriate destruction of red
blood cells) secondary to a pyruvate kinase deficiency (the final enzyme in glycolysis).
What best describes the mechanism of her hemolytic anemia? - ANS--Inadequate ATP
resulting in failure of primary active transport and subsequent cell damage
-A deficiency in the final enzyme of glycolysis would significantly reduce ATP production
and in red blood cells, which lack mitochondria, glycolysis is the principal source of
ATP. Pumps relying on ATP, primary active transporters, would fail leading to cell
