Acids and Bases - AP Chemistry
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Which of the following will result when a base and an acid react with one another?
Which of the following will result when a base and an acid react with one another?
Acids are able to donate protons whereas bases can donate hydroxyl groups. The general acid-base reaction will be a double-replacement reaction in which the proton of the acid binds the hydroxide of thee base, and the cation of the base binds the anion of the acid to form a salt. The products of this reaction are a salt and water. This is called a neutralization reaction.
Acids are able to donate protons whereas bases can donate hydroxyl groups. The general acid-base reaction will be a double-replacement reaction in which the proton of the acid binds the hydroxide of thee base, and the cation of the base binds the anion of the acid to form a salt. The products of this reaction are a salt and water. This is called a neutralization reaction.
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What is the conjugate base of nitric acid 
?
What is the conjugate base of nitric acid
Every acid has a conjugate base and every base has a conjugate acid. For any acid, the conjugate base is the negatively charged ion that is created when the acid dissociates in solution.
Nitric acid dissociates in solution based on the following reaction:
The nitrate ion, 
, is created following the dissociation of nitric acid. This means that the nitrate ion is the conjugate base of nitric acid.
Every acid has a conjugate base and every base has a conjugate acid. For any acid, the conjugate base is the negatively charged ion that is created when the acid dissociates in solution.
Nitric acid dissociates in solution based on the following reaction:
The nitrate ion,
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Which of the following salts will result in an acidic solution?
Which of the following salts will result in an acidic solution?
A salt will dissolve in water completely, existing as the individual ions that make up the compound. These ions can be thought of as the conjugate bases and acids that result from the dissociation of the reactant acids and bases. If the conjugate acid of a weak base is present in the solution, then it will become deprotonated, releasing protons into the water and lowering the pH. To answer this question, we are looking for a salt in which one of the ions created is a conjugate acid of a weak base. Let's look at a few examples in order to find the right answer:
1. 
will dissociate into sodium and fluoride ions. Sodium is the metal found on sodium hydroxide. Since sodium hydroxide is considered a strong base, the sodium ions will NOT attach to any hydroxide ions in solution. Fluoride ions, on the other hand, are the conjugate base of hydrofluoric acid, a weak acid. This means that some of the fluoride ions will attach to protons in solution, effectively raising the pH. This results in a basic solution.
2. 
is an example of a salt that will result in a neutral solution. Because lithium ions come from the strong base lithium hydroxide, and bromide ions come from the strong acid hydrobromic acid, neither of these ions will be involved in an acid/base reaction. This results in a solution with a pH of 7.
has two ions: ammonium ions and chloride ions. Chloride ions are the conjugate base of hydrochloric acid, a very strong acid. Ammonium ions, however, are the conjugate acid of ammonia, a weak base. This means that some of the ammonium ions will become deprotonated, and release protons into the solution. this results in an acidic solution.
A salt will dissolve in water completely, existing as the individual ions that make up the compound. These ions can be thought of as the conjugate bases and acids that result from the dissociation of the reactant acids and bases. If the conjugate acid of a weak base is present in the solution, then it will become deprotonated, releasing protons into the water and lowering the pH. To answer this question, we are looking for a salt in which one of the ions created is a conjugate acid of a weak base. Let's look at a few examples in order to find the right answer:
1.
2.
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Which of the following aqueous compounds is a Brønsted-Lowry acid?
Which of the following aqueous compounds is a Brønsted-Lowry acid?
A Brønsted-Lowry acid is an ionic compound that donates a proton, when the compound is placed in water.
HF and NaOH are the only ionic compounds of the given answer options; all the others are covalent compounds. When dissolved in water, only HF will donate protons.
Thus, HF is the only given Brønsted-Lowry acid.
A Brønsted-Lowry acid is an ionic compound that donates a proton, when the compound is placed in water.
HF and NaOH are the only ionic compounds of the given answer options; all the others are covalent compounds. When dissolved in water, only HF will donate protons.
Thus, HF is the only given Brønsted-Lowry acid.
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Which of the following is not a strong acid?
Which of the following is not a strong acid?
An acid is classified as strong if it completely dissociates into ions in water. Some examples of common strong acids: 
is not a strong acid because it doesn't ionize completely in solution.
An acid is classified as strong if it completely dissociates into ions in water. Some examples of common strong acids:
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Which of the following compounds may be classified as an Arrhenius acid?
Which of the following compounds may be classified as an Arrhenius acid?
By definition, and Arrhenius acid will dissociate in water to release 
. 
will dissociate into 
and 
in solution. The increased concentration of 
causes a drop in pH of the solution. In general, if a hydrogen atom is bound to a very electronegative atom, like in the case of 
, fluorine tends to take the electron away from hydrogen, resulting in ions.
By definition, and Arrhenius acid will dissociate in water to release
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Which of the following is not an acid?
Which of the following is not an acid?
or ammonia is a complicated molecule. It's a kind of molecule that we call amphoteric, meaning that it can be an acid or a base. However, because ammonia plays the role of a very weak base, it's mostly thought of as having basic qualities. It has the ability to bind with acids to create an ammonium salt or act as a proton acceptor and become ammonium (acid).
Also, commonly, acids have the 
format, where 
represents a halogen. In another construct, acids ideally have protons that they can donate - this can be observed in 
and 
.
Also, commonly, acids have the
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Which of the following is not a base?
Which of the following is not a base?
Commonly, bases have the 
format, where 
is any metallic element from the first two columns of the periodic table. This is seen with 
, 
, and 
. The remaining two options are essentially different "versions" of the same molecule - one just happens to be the protonated form (
).
While 
is technically amphoteric, it's more so thought of in terms of its basic qualities. When it does act as an acid, it's a very weak acid. Ammonia can easily become ammonium, a proton donator, due to the lone pair of electrons that continue to orbit around the nitrogen center.
Commonly, bases have the
While
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There are hydrogen ions in a solution with a pH of 3 than in a solution with a pH of 6.
There are hydrogen ions in a solution with a pH of 3 than in a solution with a pH of 6.
Each whole number on the pH scale represents a factor of ten difference in concentration of hydrogen ions. We con verify this by finding the hydrogen ion concentrations for the two given pH values.
If we take the ratio of these values, we can see that there is a difference of 1000-times more protons in the solution with a pH of 3.
Each whole number on the pH scale represents a factor of ten difference in concentration of hydrogen ions. We con verify this by finding the hydrogen ion concentrations for the two given pH values.
If we take the ratio of these values, we can see that there is a difference of 1000-times more protons in the solution with a pH of 3.
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A sample of gastric juice has a pH of 2.5. What is the hydrogen ion concentration in this secretion?
A sample of gastric juice has a pH of 2.5. What is the hydrogen ion concentration in this secretion?
The concentration of hydrogen ions must lie somewhere between 
and 
; alternatively stated, it is between 
and 
. The pH of a solution with hydrogen ion concentration of 
will be 3, and the pH of a solution with hydrogen ion concentration 
will be 2; thus, our concentration must lie between these two values, since our pH is 2.5
To find the exact concentration, you must be familiar with the logarithmic scale. A difference of 0.5 is equivalent to a log of 3.
Our answer must therefore be 
, or 
.
We can calculate the pH in reverse to check our answer.
The concentration of hydrogen ions must lie somewhere between
To find the exact concentration, you must be familiar with the logarithmic scale. A difference of 0.5 is equivalent to a log of 3.
Our answer must therefore be
We can calculate the pH in reverse to check our answer.
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Sodium hydroxide is a strong base. What is the pH of a 0.02M sodium hydroxide solution?
Sodium hydroxide is a strong base. What is the pH of a 0.02M sodium hydroxide solution?
Since sodium hydroxide is a strong base, it will dissociate completely in water. This means that the concentration of the base will be equal to the concentration of hydroxide ions after the reaction runs to completion.
We can find the concentration of hydroxide ions via stoichiometry. One hydroxide ion is created from each molecule of sodium hydroxide that dissociates.
Since we have the concentration of hydroxide ions, we can solve for the pOH of the solution.
The question asks us to find the pH of the solution, so we will need to convert pOH to pH. To do so, we simply subtract the pOH from 14.
The pH of the solution is 12.3. Because sodium hydroxide is a strong base, it makes sense that the pH is above 7.
Since sodium hydroxide is a strong base, it will dissociate completely in water. This means that the concentration of the base will be equal to the concentration of hydroxide ions after the reaction runs to completion.
We can find the concentration of hydroxide ions via stoichiometry. One hydroxide ion is created from each molecule of sodium hydroxide that dissociates.
Since we have the concentration of hydroxide ions, we can solve for the pOH of the solution.
The question asks us to find the pH of the solution, so we will need to convert pOH to pH. To do so, we simply subtract the pOH from 14.
The pH of the solution is 12.3. Because sodium hydroxide is a strong base, it makes sense that the pH is above 7.
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Acids and bases can be described in three principal ways. The Arrhenius definition is the most restrictive. It limits acids and bases to species that donate protons and hydroxide ions in solution, respectively. Examples of such acids include HCl and HBr, while KOH and NaOH are examples of bases. When in aqueous solution, these acids proceed to an equilibrium state through a dissociation reaction.
All of the bases proceed in a similar fashion.
The Brønsted-Lowry definition of an acid is a more inclusive approach. All Arrhenius acids and bases are also Brønsted-Lowry acids and bases, but the converse is not true. Brønsted-Lowry acids still reach equilibrium through the same dissociation reaction as Arrhenius acids, but the acid character is defined by different parameters. The Brønsted-Lowry definition considers bases to be hydroxide donors, like the Arrhenius definition, but also includes conjugate bases such as the A- in the above reaction. In the reverse reaction, A- accepts the proton to regenerate HA. The Brønsted-Lowry definition thus defines bases as proton acceptors, and acids as proton donors.
The pH of a solution of 
is lowered from 4 to 3, and then from 3 to 2. Which of the following is the most accurate description of what happens during these transitions?
Acids and bases can be described in three principal ways. The Arrhenius definition is the most restrictive. It limits acids and bases to species that donate protons and hydroxide ions in solution, respectively. Examples of such acids include HCl and HBr, while KOH and NaOH are examples of bases. When in aqueous solution, these acids proceed to an equilibrium state through a dissociation reaction.
All of the bases proceed in a similar fashion.
The Brønsted-Lowry definition of an acid is a more inclusive approach. All Arrhenius acids and bases are also Brønsted-Lowry acids and bases, but the converse is not true. Brønsted-Lowry acids still reach equilibrium through the same dissociation reaction as Arrhenius acids, but the acid character is defined by different parameters. The Brønsted-Lowry definition considers bases to be hydroxide donors, like the Arrhenius definition, but also includes conjugate bases such as the A- in the above reaction. In the reverse reaction, A- accepts the proton to regenerate HA. The Brønsted-Lowry definition thus defines bases as proton acceptors, and acids as proton donors.
The pH of a solution of
The pH scale is logarithmic. Every pH unit drop corresponds to a tenfold increase in protons.
The pH scale is logarithmic. Every pH unit drop corresponds to a tenfold increase in protons.
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Acids and bases can be described in three principal ways. The Arrhenius definition is the most restrictive. It limits acids and bases to species that donate protons and hydroxide ions in solution, respectively. Examples of such acids include HCl and HBr, while KOH and NaOH are examples of bases. When in aqueous solution, these acids proceed to an equilibrium state through a dissociation reaction.
All of the bases proceed in a similar fashion.
The Brønsted-Lowry definition of an acid is a more inclusive approach. All Arrhenius acids and bases are also Brønsted-Lowry acids and bases, but the converse is not true. Brønsted-Lowry acids still reach equilibrium through the same dissociation reaction as Arrhenius acids, but the acid character is defined by different parameters. The Brønsted-Lowry definition considers bases to be hydroxide donors, like the Arrhenius definition, but also includes conjugate bases such as the A- in the above reaction. In the reverse reaction, A- accepts the proton to regenerate HA. The Brønsted-Lowry definition thus defines bases as proton acceptors, and acids as proton donors.
A scientist is studying an aqueous sample of 
, and finds that the hydroxide concentration is 
. Which of the following is true?
Acids and bases can be described in three principal ways. The Arrhenius definition is the most restrictive. It limits acids and bases to species that donate protons and hydroxide ions in solution, respectively. Examples of such acids include HCl and HBr, while KOH and NaOH are examples of bases. When in aqueous solution, these acids proceed to an equilibrium state through a dissociation reaction.
All of the bases proceed in a similar fashion.
The Brønsted-Lowry definition of an acid is a more inclusive approach. All Arrhenius acids and bases are also Brønsted-Lowry acids and bases, but the converse is not true. Brønsted-Lowry acids still reach equilibrium through the same dissociation reaction as Arrhenius acids, but the acid character is defined by different parameters. The Brønsted-Lowry definition considers bases to be hydroxide donors, like the Arrhenius definition, but also includes conjugate bases such as the A- in the above reaction. In the reverse reaction, A- accepts the proton to regenerate HA. The Brønsted-Lowry definition thus defines bases as proton acceptors, and acids as proton donors.
A scientist is studying an aqueous sample of
Given the hydroxide ion concentration, we will need to work using pOH to find the pH. We know that the sum of pH and pOH is equal to 14.
Use our value for the concentration to find the pOH.
Now that we have the pOH, we can use it to solve for the pH.
Given the hydroxide ion concentration, we will need to work using pOH to find the pH. We know that the sum of pH and pOH is equal to 14.
Use our value for the concentration to find the pOH.
Now that we have the pOH, we can use it to solve for the pH.
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What is the pOH of a 
aqueous solution of 
?
What is the pOH of a
The first step for this problem is to find the pH. We can then derive the pOH from the pH value.
The pH is given by the equation 
. Since hydrochloric acid is monoprotic, the concentration of the solution is equal to the concentration of protons.
Using this value and the pH equation, we can calculate the pH.
Now we can find the pOH. The sum of the pH and the pOH is always 14.
The pOH of the solution is 7.8.
Alternatively, a shortcut can be used to estimate the pH. If 
is in the form 
, then pH is roughly 
.
For this question, this shortcut gets us a pH of 6.4, which produces a pOH of 7.6; very close to the real answer!
The first step for this problem is to find the pH. We can then derive the pOH from the pH value.
The pH is given by the equation
Using this value and the pH equation, we can calculate the pH.
Now we can find the pOH. The sum of the pH and the pOH is always 14.
The pOH of the solution is 7.8.
Alternatively, a shortcut can be used to estimate the pH. If
For this question, this shortcut gets us a pH of 6.4, which produces a pOH of 7.6; very close to the real answer!
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An arterial blood sample from a patient has a pH of 7.4. One day later, the same patient has an arterial blood pH of 7.15. How many times more acidic is the patient's blood on the second day?
An arterial blood sample from a patient has a pH of 7.4. One day later, the same patient has an arterial blood pH of 7.15. How many times more acidic is the patient's blood on the second day?
The equation to calculate pH is:
The normal pH of arterial blood is around 7.4. This reflects a concentration of hydrogen ions that can be found using the pH equation.
Using similar calculations for the second blood sample, we can find the hydrogen ion concentration again.
Now that we have both concentrations, can find the ratio of the acidity of the two samples.
You may know from biological sciences that this is approaching a lethal level of acidosis.
The equation to calculate pH is:
The normal pH of arterial blood is around 7.4. This reflects a concentration of hydrogen ions that can be found using the pH equation.
Using similar calculations for the second blood sample, we can find the hydrogen ion concentration again.
Now that we have both concentrations, can find the ratio of the acidity of the two samples.
You may know from biological sciences that this is approaching a lethal level of acidosis.
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You are presented with a solution that has a pOH of 2.13. What is the pH of this solution?
You are presented with a solution that has a pOH of 2.13. What is the pH of this solution?
pH and pOH are the log concentrations of protons and hydroxide ions, respectively.
The sum of pH and pOH is always 14. This is because the product of proton concentration and hydroxide concentration must always equal the equilibrium constant for the ionization of water, which is equal to 
.
In this question, we know that the pOH is equal to 2.13, allowing us to solve for the pH.
pH and pOH are the log concentrations of protons and hydroxide ions, respectively.
The sum of pH and pOH is always 14. This is because the product of proton concentration and hydroxide concentration must always equal the equilibrium constant for the ionization of water, which is equal to
In this question, we know that the pOH is equal to 2.13, allowing us to solve for the pH.
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What is the pH for a 0.05M solution of hydrochloric acid?
What is the pH for a 0.05M solution of hydrochloric acid?
Hydrochloric acid is a strong monoprotic acid, meaning that it will dissociate completely in solution and generate one proton from each acid molecule. This means that a 0.05M solution of hydrochloric acid will result in a 0.05M concentration of protons.
The equation for pH is as follows:
Hydrochloric acid is a strong monoprotic acid, meaning that it will dissociate completely in solution and generate one proton from each acid molecule. This means that a 0.05M solution of hydrochloric acid will result in a 0.05M concentration of protons.
The equation for pH is as follows:
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Hydrofluoric acid has a 
value of 
. What is the pH of a 
solution of hydrofluoric acid?
Hydrofluoric acid has a
Hydrofluoric acid is a weak acid, meaning that we will need to use an ICE table in order to find the pH of the solution.
The balanced reaction for hydrofluoric acid in water is:
I: Before the reaction proceeds, we have 0.04M of hydrofluoric acid. Since water is a liquid, its concentration is irrelevant for the equilibrium expression. There are also no products yet made.
C: Once the reaction reaches equilibrium, both the hydronium and fluoride concentrations will have increased by an unknown concentration. We will call this increase 
. Conversely, the concentration of hydrofluoric acid concentration will have decreased by the same amount, in this case 
.
E: Using the equilibrium expression and making it equal to the acid dissociation constant, we can solve for 
.
Note: Since the value for 
is going to be very small compared to the initial acid concentration, we can disregard the 
in the denominator:
Keep in mind that 
is equal to the concentration of hydronium ions now in the solution.
Use this value in the equation for pH:
Hydrofluoric acid is a weak acid, meaning that we will need to use an ICE table in order to find the pH of the solution.
The balanced reaction for hydrofluoric acid in water is:
I: Before the reaction proceeds, we have 0.04M of hydrofluoric acid. Since water is a liquid, its concentration is irrelevant for the equilibrium expression. There are also no products yet made.
C: Once the reaction reaches equilibrium, both the hydronium and fluoride concentrations will have increased by an unknown concentration. We will call this increase
E: Using the equilibrium expression and making it equal to the acid dissociation constant, we can solve for
Note: Since the value for
Keep in mind that
Use this value in the equation for pH:
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What is the pH of a 
ammonia solution if its 
value is 
?
What is the pH of a
Ammonia is a weak base, meaning that we will require an ICE table in order to determine the pH of the solution.
Let's look at the dissociation of ammonia:
I: Before the reaction proceeds, ammonia has a concentration of 0.02M. No product has yet been made.
C: When the reaction is at equilibrium, the products will increase by a concentration of 
. Conversely, ammonia's concentration will decrease by the same amount, 
.
E: By setting the equilibrium expression equal to the base dissociation constant, we can solve for the value of 
.
Note: because the value for 
will be so much less than the initial base concentration, we can omit it from the denominator:
Keep in mind that is equal to the concentration of hydroxide ions now in the solution.
Use this value in the equation for pOH:
Remember that the sum of pH and pOH is always 14. To find the pH, subtract the pOH from 14.
Ammonia is a weak base, meaning that we will require an ICE table in order to determine the pH of the solution.
Let's look at the dissociation of ammonia:
I: Before the reaction proceeds, ammonia has a concentration of 0.02M. No product has yet been made.
C: When the reaction is at equilibrium, the products will increase by a concentration of
E: By setting the equilibrium expression equal to the base dissociation constant, we can solve for the value of
Note: because the value for
Keep in mind that
Use this value in the equation for pOH:
Remember that the sum of pH and pOH is always 14. To find the pH, subtract the pOH from 14.
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You find a bottle in a lab that has a 
solution of acid. The acid has the following dissociative properties:
What is the pH of this solution?
You find a bottle in a lab that has a
What is the pH of this solution?
is a strong acid, meaning it will completely dissociate in solution. As such, the concentration of the acid will be equal to the proton concentration. Thus, to find pH, you should just plug the molar concentration of the acid solution into the pH formula.
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