Biochemistry - GRE Subject Test: Biochemistry, Cell, and Molecular Biology
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Which three elements are capable of participating in hydrogen bonding?
Which three elements are capable of participating in hydrogen bonding?
A hydrogen bond is the weak attraction of a covalently bonded hydrogen to nearby fluorine, oxygen, or nitrogen (FON) atoms. These attractions can occur within a single molecule (intramolecular) or between two distinct molecules in close proximity (intermolecular). Hydrogen bonds give water its cohesiveness and its surface tension.
A hydrogen bond is the weak attraction of a covalently bonded hydrogen to nearby fluorine, oxygen, or nitrogen (FON) atoms. These attractions can occur within a single molecule (intramolecular) or between two distinct molecules in close proximity (intermolecular). Hydrogen bonds give water its cohesiveness and its surface tension.
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The strength of bonds and intermolecular forces, from strong to weak, can be recalled by the use of the mnemonic "I Can't Handle Dirty Vans," which stands for __________.
The strength of bonds and intermolecular forces, from strong to weak, can be recalled by the use of the mnemonic "I Can't Handle Dirty Vans," which stands for __________.
Ionic bonds form when one or more electrons from an atom are removed and attached to another atom resulting in positive and negative ions that attract each other. Sodium chloride is an example of an ionic compound. Covalent bonds form when one or more pairs of electrons are shared by two atoms. Hydrochloric acid is an example of a covalent compound. A hydrogen bond is a force of attraction between a hydrogen atom in one molecule and a small atom of high electronegativity (oxygen, nitrogen, or fluorine) in another molecule. Water molecules are capable of intermolecular hydrogen bonds. A dipole-dipole bond is an attractive force between the positive end of one polar molecule and the negative end of another polar molecule. Iodine monochloride molecules show dipole-dipole attraction. Van der Waals forces arise from spontaneous changes in electron density; these occur in all chemical molecules regardless of composition and are extremely weak interactions.
Ionic bonds form when one or more electrons from an atom are removed and attached to another atom resulting in positive and negative ions that attract each other. Sodium chloride is an example of an ionic compound. Covalent bonds form when one or more pairs of electrons are shared by two atoms. Hydrochloric acid is an example of a covalent compound. A hydrogen bond is a force of attraction between a hydrogen atom in one molecule and a small atom of high electronegativity (oxygen, nitrogen, or fluorine) in another molecule. Water molecules are capable of intermolecular hydrogen bonds. A dipole-dipole bond is an attractive force between the positive end of one polar molecule and the negative end of another polar molecule. Iodine monochloride molecules show dipole-dipole attraction. Van der Waals forces arise from spontaneous changes in electron density; these occur in all chemical molecules regardless of composition and are extremely weak interactions.
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A mnemonic for remembering whether energy is required or released when chemical bonds are formed is __________.
A mnemonic for remembering whether energy is required or released when chemical bonds are formed is __________.
Energy is absorbed when bonds break. The energy required to break the bond is absorbed from the surroundings. You have to put energy into a molecule to break its chemical bond.
Energy is released when bonds form. Bond formation represents a stable configuration of atoms. If breaking a bond absorbs energy, forming a bond must release energy; thus, the mnemonic BARF—Break (a bond), Absorb (energy), Release (energy), Form (a bond).
SCAN is the mnemonic for the magnetic field induced in a coil—south clockwise, anticlockwise north. PASS stands for pull, aim, squeeze, sweep—how to use a fire extinguisher. RICE is the treatment for an injury to a joint: rest, ice, compression, elevation. LEO says GER is a mnemonic for loss of electrons is oxidation, gain of electrons is reduction.
Energy is absorbed when bonds break. The energy required to break the bond is absorbed from the surroundings. You have to put energy into a molecule to break its chemical bond.
Energy is released when bonds form. Bond formation represents a stable configuration of atoms. If breaking a bond absorbs energy, forming a bond must release energy; thus, the mnemonic BARF—Break (a bond), Absorb (energy), Release (energy), Form (a bond).
SCAN is the mnemonic for the magnetic field induced in a coil—south clockwise, anticlockwise north. PASS stands for pull, aim, squeeze, sweep—how to use a fire extinguisher. RICE is the treatment for an injury to a joint: rest, ice, compression, elevation. LEO says GER is a mnemonic for loss of electrons is oxidation, gain of electrons is reduction.
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Which of the following forces is strongest between molecules of hydrochloric acid (HCl)?
Which of the following forces is strongest between molecules of hydrochloric acid (HCl)?
Since hydrochloric acid has a partial positive charge on the hydrogen and a partial negative charge on the chlorine, the molecules will have dipole-dipole interactions between them. Although hydrogen bonding is a stronger force, a hydrogen must be attached to a nitrogen, oxygen, or fluorine in order to exhibit hydrogen bonding.
Since hydrochloric acid has a partial positive charge on the hydrogen and a partial negative charge on the chlorine, the molecules will have dipole-dipole interactions between them. Although hydrogen bonding is a stronger force, a hydrogen must be attached to a nitrogen, oxygen, or fluorine in order to exhibit hydrogen bonding.
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Which of the following molecules is not capable of hydrogen bonding?
Which of the following molecules is not capable of hydrogen bonding?
Hydrogen bonding is possible when a hydrogen atom is attached to a nitrogen, oxygen, or fluorine. Of the following options, hydrochloric acid 
is the only option that does not fit the criteria.
Hydrogen bonding is possible when a hydrogen atom is attached to a nitrogen, oxygen, or fluorine. Of the following options, hydrochloric acid
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Which of the following statements is not true regarding Gibbs free energy, 
?
Which of the following statements is not true regarding Gibbs free energy,
If the 
of a reaction is less than zero, the reaction will in fact be exergonic. These reactions will be favorable and spontaneous, and energy is released in these reactions. Thus, endergonic is incorrect.
If the
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The equilibrium constant 
of any given chemical reaction is __________ on the temperature and pressure of the reactants and products and is __________ of the reaction rate.
The equilibrium constant
The temperature and pressure of the reactants and products of any given reaction will determine the value of 
. However, this is entirely dependent of the reaction rate, which is determined by how the concentrations of the reactants and products change over the course of the reaction. Additionally, every reaction is unique, so "one-half" or any other exact metric cannot be applied as the definition.
The temperature and pressure of the reactants and products of any given reaction will determine the value of
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Which of the following best describes a reaction that has reached equilibrium?
Which of the following best describes a reaction that has reached equilibrium?
In equilibrium, both the forward and reverse reactions continue to occur, but they do so in a way that is equal and thus, there is no net change of reactants and products in the system. 
is zero in this case because net changes to the system have ceased, and thus the free energy is no longer in flux.
In equilibrium, both the forward and reverse reactions continue to occur, but they do so in a way that is equal and thus, there is no net change of reactants and products in the system.
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__________ reactions have a 
that is less than zero, and thus they occur spontaneously. This is because the products in these reactions have lower bond energies than the reactants, and when that energy is released it is converted to __________.
__________ reactions have a
Exothermic reactions release heat (think exothermic = explosion = creates heat), and this is due to the release of energy from the reactant bonds. These reactions have 
less than zero. Endothermic reactions are just the opposite and actually require energy to occur, and therefore do not occur spontaneously nor release heat.
Exothermic reactions release heat (think exothermic = explosion = creates heat), and this is due to the release of energy from the reactant bonds. These reactions have
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What is the appropriate way to describe a solution with a pH of 3 compared to a solution with a pH of 6?
What is the appropriate way to describe a solution with a pH of 3 compared to a solution with a pH of 6?
The pH scale is logarithmic, meaning every whole number change on the scale reflects a ten-fold change in acidity. Since a pH of 3 is three numbers higher than a pH of 6, we can find the change in acidity by taking 10 to the third power.
The solution with a pH of 3 is 1000 times more acidic than the solution with a pH of 6.
The pH scale is logarithmic, meaning every whole number change on the scale reflects a ten-fold change in acidity. Since a pH of 3 is three numbers higher than a pH of 6, we can find the change in acidity by taking 10 to the third power.
The solution with a pH of 3 is 1000 times more acidic than the solution with a pH of 6.
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What is the pH of a 0.03M hydrochloric acid solution?
What is the pH of a 0.03M hydrochloric acid solution?
Since hydrochloric acid is considered a strong acid, we can assume that the acid will dissociate completely, leaving us with a 0.03M concentration of hydronium ions. Knowing this, we can calculate the pH by taking the negative log of the hydronium concentration:
Since hydrochloric acid is considered a strong acid, we can assume that the acid will dissociate completely, leaving us with a 0.03M concentration of hydronium ions. Knowing this, we can calculate the pH by taking the negative log of the hydronium concentration:
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What is the concentration of hydroxide ions in a 1M hydrochloric acid solution?
What is the concentration of hydroxide ions in a 1M hydrochloric acid solution?
To solve this question we need to first look at the relationship between hydroxide and hydrogen ion concentrations:
where 
is concentration of hydrogen ions and 
is the concentration of hydroxide ions. Solve for 
:
We can solve for the concentration of hydrogen ions in this solution by writing the dissociation of hydrochloric acid in solution:
The question states that it is a 1M solution. Since 
and 
are in 1:1 ratio, the concentration of hydrogen ions will equal the concentration 
; therefore, 
. Note that this won’t be the case if the acid was weak. For a weak acid, the concentration of 
will be less than the concentration of acid, even if it was 1:1 ratio. This occurs because a weak acid does not dissociate completely.
We can now use the 
to solve for 
.
Therefore, concentration of hydroxide ions in this solution is 
To solve this question we need to first look at the relationship between hydroxide and hydrogen ion concentrations:
where
We can solve for the concentration of hydrogen ions in this solution by writing the dissociation of hydrochloric acid in solution:
The question states that it is a 1M solution. Since
We can now use the
Therefore, concentration of hydroxide ions in this solution is
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Which of the following substances is considered a Lewis acid?
Which of the following substances is considered a Lewis acid?
Recall that acids and bases can be defined in three different ways. First, the Arrhenius definition states that an acid is a substance that increases the concentration of hydrogen ions in solution whereas a base decreases hydrogen ions concentration. Second, Bronsted-Lowry definition states that an acid is any substance that donates a proton whereas a base is any substance that accepts a proton. Finally, Lewis definition states that an acid is any substance that accepts an electron pair whereas a base is a substance that donates an electron pair.
We have two substances in this question. 
, or borane, is considered a Lewis acid because it accepts an electron pair. Boron has four orbitals in its outermost shell. If we look at Boron in borane, we will notice that three orbitals are occupied by the electrons in the three single bonds (bound to hydrogen) whereas the last orbital is empty and is free to accept electrons. Since it accepts electrons, borane is considered a lewis acid. 
, or ammonia, is a lewis base. If we look at the nitrogen atom in ammonia, we will notice that all of its orbitals are occupied (three orbitals are occupied with the three bonds to hydrogen atoms and the last orbital is occupied with a lone electron pair). Since it has extra electrons in the last orbital, ammonia can donate electrons and is considered a lewis base.
Recall that acids and bases can be defined in three different ways. First, the Arrhenius definition states that an acid is a substance that increases the concentration of hydrogen ions in solution whereas a base decreases hydrogen ions concentration. Second, Bronsted-Lowry definition states that an acid is any substance that donates a proton whereas a base is any substance that accepts a proton. Finally, Lewis definition states that an acid is any substance that accepts an electron pair whereas a base is a substance that donates an electron pair.
We have two substances in this question.
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Solutions A and B are both made up of an acidic solution. After analysis, it is observed that the 
of solution A is higher whereas the 
of acid in solution B is lower. What can be concluded about these results?
Solutions A and B are both made up of an acidic solution. After analysis, it is observed that the
The question states that the 
of solution A is higher. The definition of 
is:
If we rearrange and solve for concentration of hydroxide ions, we get
This means that 
decreases as 
increases. The relationship between hydroxide ion and hydrogen ion is as follows
Note that the hydroxide ion concentration is inversely proportional to that of hydrogen ions; therefore, lower hydroxide ion concentration leads to higher hydrogen ion concentration and higher acidity. Since solution A has the higher 
, its hydroxide ion concentration is lower than solution B. This means that solution A has higher hydrogen ion concentration and, therefore, is more acidic than solution B.
The question also states that the 
of solution B is lower. Recall that as 
of an acid decreases it becomes more acidic. Based on this, we conclude that solution B is more acidic. The two results given in this question conflict each other; therefore, these results seem invalid.
The question states that the
If we rearrange and solve for concentration of hydroxide ions, we get
This means that
Note that the hydroxide ion concentration is inversely proportional to that of hydrogen ions; therefore, lower hydroxide ion concentration leads to higher hydrogen ion concentration and higher acidity. Since solution A has the higher
The question also states that the
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The pH of a solution __________ when the acid dissociation constant __________.
The pH of a solution __________ when the acid dissociation constant __________.
Acid dissociation constant, or 
, for a prototypical acid-base reaction is defined as
where 
is an acid and 
is its conjugate base. Based on this equation, we can determine that 
and 
are directly proportional to one another; therefore, increasing 
will increase 
and vice versa.
Recall the definition of 
Solving for 
gives us
This means that increasing pH will decrease 
and vice versa (has the opposite effect on each other); therefore, 
and 
also have an opposite effect on each other.
Acid dissociation constant, or
where
Recall the definition of
Solving for
This means that increasing pH will decrease
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A buffer can be created by adding equal amounts of weak acid and its conjugate base. What additional information is needed to determine the pKa of a buffer made in this manner?
A buffer can be created by adding equal amounts of weak acid and its conjugate base. What additional information is needed to determine the pKa of a buffer made in this manner?
The buffer is made by using weak acid and its conjugate base. The relationship between the concentration of the components (acid and conjugate base), pKa, and pH can be determined by using the Henderson-Hasselbalch equation.
where 
is weak acid and 
is the conjugate base. We know that equal amounts of 
and 
are added; therefore, 
for buffer solutions made in this manner. To calculate the pKa of the solution we need the pH.
The buffer is made by using weak acid and its conjugate base. The relationship between the concentration of the components (acid and conjugate base), pKa, and pH can be determined by using the Henderson-Hasselbalch equation.
where
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A researcher adds 
acid to 
. The concentration of hydrogen ions is __________ as the concentration of hydroxide ions.
A researcher adds
Hydrochloric acid (
) and sodium hydroxide (
) are both strong reagents. Adding equal amounts of strong acid to a strong base neutralizes the solution and gives the solution a neutral pH of 7. This means that the concentration of hydrogen ions and hydroxide ions are equal to each other. If pH was greater than 7 (basic pH), then the hydroxide ion concentration would be higher and if pH was less than 7 (acidic pH) then hydrogen ion concentration would be higher.
Hydrochloric acid (
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Solution A contains a weak acid and a weak base whereas solution B contains a weak acid and a strong base. What can you conclude about these two solutions?
I. Solution B will have a higher 
II. Solution B will have a higher pOH
III. Solution A will have a lower concentration of hydroxide ions
Solution A contains a weak acid and a weak base whereas solution B contains a weak acid and a strong base. What can you conclude about these two solutions?
I. Solution B will have a higher
II. Solution B will have a higher pOH
III. Solution A will have a lower concentration of hydroxide ions
Solution A has two weak reagents whereas solution B contains a strong base. This means that solution B will be more basic, will have a higher concentration of hydroxide ions, and a higher pH. 
is a constant and is not altered by the relative reagents (it is always equal to 
). Recall that pOH is defined as
This equation suggests that pOH decreases as the hydroxide ion concentration increases. Since it has the higher hydroxide ion concentration, solution B will have a lower pOH.
Solution A has two weak reagents whereas solution B contains a strong base. This means that solution B will be more basic, will have a higher concentration of hydroxide ions, and a higher pH.
This equation suggests that pOH decreases as the hydroxide ion concentration increases. Since it has the higher hydroxide ion concentration, solution B will have a lower pOH.
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What is the pH of a solution composed of 
acetic acid and 
acetate?
for acetic acid is 
What is the pH of a solution composed of
Since this problem involves both the acid and the conjugate base of the acid, we can use the Henderson-Hasselbach equation in order to determine the pH of the solution:
Since this problem involves both the acid and the conjugate base of the acid, we can use the Henderson-Hasselbach equation in order to determine the pH of the solution:
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If a 
solution of hydrofluoric acid is created, what fluoride ion concentration must be present in order to make the new pH of the solution equal to 
?
for hydrofluoric acid is 
If a
In order to determine what concentration of fluoride is needed, we can use the Henderson-Hasselbach equation:
In order to determine what concentration of fluoride is needed, we can use the Henderson-Hasselbach equation:
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