General Chemistry - GRE Subject Test: Chemistry
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100mL of an unknown solution of NaOH is titrated with 3M HCl until neutralized. The resulting solution is evaporated, and 3.0g of white crystal are recovered. What was the concentration of the NaOH solution?
100mL of an unknown solution of NaOH is titrated with 3M HCl until neutralized. The resulting solution is evaporated, and 3.0g of white crystal are recovered. What was the concentration of the NaOH solution?
In the neutralization reaction between NaOH and HCl, NaCl salt is formed. When the solution is evaporated, this salt is left behind.
3.0g of NaCl is equivalent to 0.05mol NaCl. Since the titration is between a strong acid and a strong base, all of the NaOH in the original solution is converted to NaCl in a one-to-one ratio, meaning that mol NaCl = mol NaOH.
We now know that there was 0.05mol NaOH in the 100mL solution, so the concentration must have been 
.
In the neutralization reaction between NaOH and HCl, NaCl salt is formed. When the solution is evaporated, this salt is left behind.
3.0g of NaCl is equivalent to 0.05mol NaCl. Since the titration is between a strong acid and a strong base, all of the NaOH in the original solution is converted to NaCl in a one-to-one ratio, meaning that mol NaCl = mol NaOH.
We now know that there was 0.05mol NaOH in the 100mL solution, so the concentration must have been
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What volume of 0.375M H2SO4 is needed to fully neutralize 0.5L of 0.125M NaOH?
What volume of 0.375M H2SO4 is needed to fully neutralize 0.5L of 0.125M NaOH?
This question requires use of the simple titration equation M1V1 = M2V2. The key is to identify that sulfuric acid has two equivalents of acidic hydrogens while NaOH has only one hydroxide equivalent. All wrong answer choices result from making this mistake or other calculation errors.
This question requires use of the simple titration equation M1V1 = M2V2. The key is to identify that sulfuric acid has two equivalents of acidic hydrogens while NaOH has only one hydroxide equivalent. All wrong answer choices result from making this mistake or other calculation errors.
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Consider the following reaction:
Which of the following changes will increase the pH of this solution?
Consider the following reaction:
Which of the following changes will increase the pH of this solution?
To answer this question you need to use Le Chatelier’s principle. Adding sodium acetate to the solution will cause it to dissociate as follows:
The dissociation reaction will produce more acetate ions. According to Le Chatelier’s principle, the increase in acetate ions will shift the equilibrium of the reaction (given in the question) to the left. This means that 
and 
will be utilized to form 
. This will cause a decrease in the amount of hydronium ions in solution. Recall that pH is increased when the concentration of hydrogen ions (or hydronium ions, 
) is decreased; therefore, adding sodium acetate will increase the pH of the solution.
Increasing acetic acid concentration will shift the equilibrium to the right and produce more hydronium ions, thereby decreasing the pH. Recall that you can never change the pKa of an acid. The pKa of acetic acid is around 4.75, and it cannot be altered. Le Chatelier’s principle only applies when there is a change in amount of aqueous or gaseous substances; liquid and solid substances will not shift the equilibrium. Changing the volume of liquid water will not change the concentration of hydronium ions.
To answer this question you need to use Le Chatelier’s principle. Adding sodium acetate to the solution will cause it to dissociate as follows:
The dissociation reaction will produce more acetate ions. According to Le Chatelier’s principle, the increase in acetate ions will shift the equilibrium of the reaction (given in the question) to the left. This means that
Increasing acetic acid concentration will shift the equilibrium to the right and produce more hydronium ions, thereby decreasing the pH. Recall that you can never change the pKa of an acid. The pKa of acetic acid is around 4.75, and it cannot be altered. Le Chatelier’s principle only applies when there is a change in amount of aqueous or gaseous substances; liquid and solid substances will not shift the equilibrium. Changing the volume of liquid water will not change the concentration of hydronium ions.
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Which of the following acids is polyprotic?
Which of the following acids is polyprotic?
Sulfuric acid (
) is considered a polyprotic acid because it has two ionizable protons in its molecular formula. The protons dissociate in an aqueous solution according to the acid-base equilibria below:
All the other acids listed in the answer choices are monoprotic.
Sulfuric acid (
All the other acids listed in the answer choices are monoprotic.
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Which of the following acids is considered polyprotic?
Which of the following acids is considered polyprotic?
Carbonic acid (
) is considered a polyprotic acid because it has two ionizable protons (
atoms) in its molecular formula. The protons dissociate in an aqueous solution according to the acid-base equilibria below:
The other acids are all monoprotic acids.
Carbonic acid (
The other acids are all monoprotic acids.
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Considering the Ka for 
is 
, what is the Kb for 
?
Considering the Ka for
The equilibrium governing the dissolution of 
in water is:
is the conjugate acid of 
. In other words, 
is the conjugate base of 
.
Using the relationship, 
, we can calculate the Kb.
Rearrange the equation and solve:
The equilibrium governing the dissolution of
Using the relationship,
Rearrange the equation and solve:
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Considering the Ka for 
is 
, what is the Kb for 
?
Considering the Ka for
The equilibrium governing the dissolution of 
in water is:
is the conjugate acid of 
. In other words, 
is the conjugate base of 
.
Using the relationship, 
, we can calculate the Kb.
Rearrange the equation and solve:
The equilibrium governing the dissolution of
Using the relationship,
Rearrange the equation and solve:
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Based on the equilibrium shown, what does 
act as?
Based on the equilibrium shown, what does
A base is a substance that can accept a proton. The conjugate base of an acid is formed when the acid donates a proton. In this case, 
is the conjugate base to the acid 
. This is because 
donates a hydrogen ion to the organic molecule to form 
, the conjugate base.
A base is a substance that can accept a proton. The conjugate base of an acid is formed when the acid donates a proton. In this case,
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Which of the following is the weakest acid?
Which of the following is the weakest acid?
(hydrofluoric acid) is the weakest acid. Fluoride ion is the most electronegative ion. Among the other halogens, its atomic radius is smaller, and therefore bonds more strongly with hydrogen and therefore does not completely dissociate in solution as compared to 
, 
, and 
. Perchloric acid is a strong acid and dissociates completely in solution.
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Based on the above balanced equation for a neutralization reaction, what is the 
concentration of a 
solution if 
of 
is needed to neutralize a 
solution of 
?
Based on the above balanced equation for a neutralization reaction, what is the
We need to convert milliliters to liters:
We need to determine the moles of 
using dimensional analysis the concentration as a conversion factor:
Based on the chemical equation given:
We can used the relationship of moles of 
and moles of 
as a conversion factor to determine the moles of 
:
Concentration in molarity can be calculated using the following formula:
Let's convert liters of 
to the mL:
Therefore, the concentration of 
is:
We need to convert milliliters to liters:
We need to determine the moles of
Based on the chemical equation given:
We can used the relationship of moles of
Concentration in molarity can be calculated using the following formula:
Let's convert liters of
Therefore, the concentration of
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Based on the above balanced equation for a neutralization reaction, how many moles of 
is formed if 
of 
is needed to neutralize a solution of ?
Based on the above balanced equation for a neutralization reaction, how many moles of
We need to convert milliliters of 
to liters:
We need to determine the moles of 
using dimensional analysis and the concentration as a conversion factor:
Based on the chemical equation given:
We can use the relationship of moles of 
and moles of as a conversion factor to determine the moles of :
We need to convert milliliters of
We need to determine the moles of
Based on the chemical equation given:
We can use the relationship of moles of
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What is the type of reaction given?
What is the type of reaction given?
The reaction given is called a neutralization reaction because the acid and base components react to counterbalance each other making them chemically neutral. This type of reaction occurs between an acid and base to form a water and a salt. A neutralization reaction between a strong acid and a strong base react to form a neutral solution of pH 7.
The reaction given is called a neutralization reaction because the acid and base components react to counterbalance each other making them chemically neutral. This type of reaction occurs between an acid and base to form a water and a salt. A neutralization reaction between a strong acid and a strong base react to form a neutral solution of pH 7.
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If 4.2 moles of 
is reacted with 3.5 moles of 
, how many grams of 
is produced?
If 4.2 moles of
is the limiting reactant because based on the equation, 
and 
react in a 1:1 mole ratio. However, there is 0.5 moles more of 
than 
therefore the amount of 
produced is limited by the amount of 
present in the reaction. Based on the equation for every 1 mole of 
reacted, 1 mole of 
was produced:
Therefore,
Therefore,
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Determine the acid dissociation constant for a 
monoprotic acid 
dissolved in the 
in which a pH meter for read pH 
for the solution.
Determine the acid dissociation constant for a
The acid dissociation constant expression for this reaction is:
Due to the dissociation of 
:
Using the following equation, we can calculate the 
concentration:
Plug the values obtained in to the acid dissociation constant expression:
The acid dissociation constant expression for this reaction is:
Due to the dissociation of
Using the following equation, we can calculate the
Plug the values obtained in to the acid dissociation constant expression:
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Which of the following would have the greatest atomic radius?
Which of the following would have the greatest atomic radius?
Atomic radius increases down each group of the periodic table and toward the left of each period. Since the elements listed are all in the same group, iodine would have the greatest atomic radius because it farther down the period compared to the others.
Atomic radius increases down each group of the periodic table and toward the left of each period. Since the elements listed are all in the same group, iodine would have the greatest atomic radius because it farther down the period compared to the others.
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Which of the following elements has the greatest atomic radius?
Which of the following elements has the greatest atomic radius?
Atomic radius can be determined using the periodic trends. Atomic radius increases to the left of a period and down a group of the periodic table. Electronegativity, in contrast, increases to the right of a period and up a group of the periodic table. Relating the two, we can see that the greater the atomic radius, the weaker its electronegativity because the electrons are farther away from the nucleus and are unable to feel the attractive force of the protons in the nucleus.
Atomic radius can be determined using the periodic trends. Atomic radius increases to the left of a period and down a group of the periodic table. Electronegativity, in contrast, increases to the right of a period and up a group of the periodic table. Relating the two, we can see that the greater the atomic radius, the weaker its electronegativity because the electrons are farther away from the nucleus and are unable to feel the attractive force of the protons in the nucleus.
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Which of the given atoms has the largest atomic radius?
Which of the given atoms has the largest atomic radius?
Lithium, boron, oxygen, and neon are all in the same row (period) of the periodic table.
The atomic radius decreases from left to right along a period due to increased effective nuclear force. From left to right the atomic number increases, indicating that more protons are added. The addition of protons increases the positive charge in the nucleus, pulling in the outer electrons by increasing the effective nuclear force, decreasing the radius.
In math terms, we can equate effective nuclear force using the force equation between two charged particles.
We can see that the farther apart the electrons and protons are, the less the force is between them.
Lithium, boron, oxygen, and neon are all in the same row (period) of the periodic table.
The atomic radius decreases from left to right along a period due to increased effective nuclear force. From left to right the atomic number increases, indicating that more protons are added. The addition of protons increases the positive charge in the nucleus, pulling in the outer electrons by increasing the effective nuclear force, decreasing the radius.
In math terms, we can equate effective nuclear force using the force equation between two charged particles.
We can see that the farther apart the electrons and protons are, the less the force is between them.
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Which of the given atoms has the smallest atomic radius?
Which of the given atoms has the smallest atomic radius?
Nitrogen, phosphorous, antimony, and bismuth are all in the same group (column) of the periodic table.
The atomic radius increases from the top of a group to the bottom, due to increased principle shell number (n). As one travels down a group, another s shell is added, meaning that electrons are added in another orbit farther from the nucleus. This serves to increase the atomic radius of the atom.
Nitrogen, phosphorous, antimony, and bismuth are all in the same group (column) of the periodic table.
The atomic radius increases from the top of a group to the bottom, due to increased principle shell number (n). As one travels down a group, another s shell is added, meaning that electrons are added in another orbit farther from the nucleus. This serves to increase the atomic radius of the atom.
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Which of the following correctly describes the trend for atomic radius in the periodic table of elements?
Which of the following correctly describes the trend for atomic radius in the periodic table of elements?
Energy level increases moving down a group of the periodic table. As energy level increases, the outer valence shell becomes more distant from the nucleus, causing atomic radius to increase.
Energy level remains constant across a period, but electrons are added within the same orbitals. When new electrons are added within the same orbital, additional protons are also added to the nucleus. This increases the effective nuclear charge, pulling the electrons closer to the nucleus. The trend for atomic radius is to decrease as we move right along a row.
This means that the general trend for atomic radius is to increase as one moves to the left and downward on the periodic table.
Energy level increases moving down a group of the periodic table. As energy level increases, the outer valence shell becomes more distant from the nucleus, causing atomic radius to increase.
Energy level remains constant across a period, but electrons are added within the same orbitals. When new electrons are added within the same orbital, additional protons are also added to the nucleus. This increases the effective nuclear charge, pulling the electrons closer to the nucleus. The trend for atomic radius is to decrease as we move right along a row.
This means that the general trend for atomic radius is to increase as one moves to the left and downward on the periodic table.
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Which of the following has the largest atomic radius?
Which of the following has the largest atomic radius?
Atomic radius increases with increasing effective nuclear charge (Z). Elements toward the right and toward the top of the periodic table have the highest Z values. Protons and electrons are added in pairs as we traverse the periodic table from left to right. A attractive force is established between the positively-charged nucleus and the negatively-charged electron cloud, which increases as the number of particles grows.
When electrons are added or taken away without the same happening to a proton, an imbalance of charge accumulates. When more electrons are present than normal, the electron cloud sags farther away from the nucleus. When fewer electrons are present than normal, the electron cloud is drawn in more tightly toward the nucleus. Atoms with extra electrons (a negative charge) will have larger nuclei than their neutral counterparts. A chloride ion will thus has a larger atomic radius than argon, a potassium ion, or a calcium ion.
Atomic radius increases with increasing effective nuclear charge (Z). Elements toward the right and toward the top of the periodic table have the highest Z values. Protons and electrons are added in pairs as we traverse the periodic table from left to right. A attractive force is established between the positively-charged nucleus and the negatively-charged electron cloud, which increases as the number of particles grows.
When electrons are added or taken away without the same happening to a proton, an imbalance of charge accumulates. When more electrons are present than normal, the electron cloud sags farther away from the nucleus. When fewer electrons are present than normal, the electron cloud is drawn in more tightly toward the nucleus. Atoms with extra electrons (a negative charge) will have larger nuclei than their neutral counterparts. A chloride ion will thus has a larger atomic radius than argon, a potassium ion, or a calcium ion.
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