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The pKa value of a compound is a numerical representation of its acidity, specifically the negative logarithm of its acid dissociation constant (Ka). It provides insight into the tendency of a compound to donate a proton (H+) in an aqueous solution. A lower pKa value indicates a stronger acid, which more readily donates a proton, while a higher pKa value suggests a weaker acid.
The pKa value of a compound is a numerical representation of its acidity, specifically the negative logarithm of its acid dissociation constant (Ka). It provides insight into the tendency of a compound to donate a proton (H+) in an aqueous solution. A lower pKa value indicates a stronger acid, which more readily donates a proton, while a higher pKa value suggests a weaker acid.
Ethers are a class of organic compounds characterized by an oxygen atom connected to two alkyl or aryl groups. They are generally represented by the formula R-O-R', where R and R' can be the same or different alkyl or aryl groups. Ethers are known for their relative chemical inertness, particularly in terms of acidity.
To understand the pKa value of an ether, it is important to recognize that ethers do not have a hydrogen atom attached to the oxygen, which is the typical site for acidity in other functional groups like alcohols or carboxylic acids. Therefore, ethers are not considered acidic under normal conditions, and they do not have a pKa value in the same sense that more acidic compounds do.
However, if we consider the hypothetical scenario where an ether could donate a proton, it would be from one of the alkyl groups attached to the oxygen. This process is highly unfavorable and would result in the formation of an unstable alkoxide ion and a carbocation, which is a very high-energy species. Consequently, the pKa of an ether, if it were to be measured, would be extremely high, reflecting its very low acidity.
In practice, the pKa values of ethers are not typically discussed in the same context as more acidic functional groups. For comparison, the pKa of a typical alcohol is in the range of 15-18, while the pKa of an ether would be estimated to be well above 30, indicating that ethers are much less acidic than alcohols.
In summary, ethers are considered to have negligible acidity in aqueous solution, and thus they do not have a meaningful pKa value in the context of acid-base chemistry. When discussing the reactivity of ethers, other properties, such as their potential to form peroxides or their role as solvents, are usually more relevant.
Ethers are a class of organic compounds characterized by an oxygen atom connected to two alkyl or aryl groups. They are generally represented by the formula R-O-R', where R and R' can be the same or different alkyl or aryl groups. Ethers are known for their relative chemical inertness, particularly in terms of acidity.
To understand the pKa value of an ether, it is important to recognize that ethers do not have a hydrogen atom attached to the oxygen, which is the typical site for acidity in other functional groups like alcohols or carboxylic acids. Therefore, ethers are not considered acidic under normal conditions, and they do not have a pKa value in the same sense that more acidic compounds do.
However, if we consider the hypothetical scenario where an ether could donate a proton, it would be from one of the alkyl groups attached to the oxygen. This process is highly unfavorable and would result in the formation of an unstable alkoxide ion and a carbocation, which is a very high-energy species. Consequently, the pKa of an ether, if it were to be measured, would be extremely high, reflecting its very low acidity.
In practice, the pKa values of ethers are not typically discussed in the same context as more acidic functional groups. For comparison, the pKa of a typical alcohol is in the range of 15-18, while the pKa of an ether would be estimated to be well above 30, indicating that ethers are much less acidic than alcohols.
In summary, ethers are considered to have negligible acidity in aqueous solution, and thus they do not have a meaningful pKa value in the context of acid-base chemistry. When discussing the reactivity of ethers, other properties, such as their potential to form peroxides or their role as solvents, are usually more relevant.
Ionized water, Equilibrium Constant
Exercise 14 - The commons between strong acids and bases
Exercise 18 - The false statement about acid-base reactions
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Ionized water, Equilibrium Constant
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Welcome to the topic of ionization of water,
where we specifically talk about ionized water equilibrium constant
of ionization of water and by the end of this section,
you will be able to explain the ionization of water,
describe how to measure the ionization of water,
and relate the equilibrium constant to the reactions covered.
Ionization of water is when it is in the form of hydrogen ions,
H plus and hydroxide ions, OH minus.
We have H plus is the hydrogen ions,
OH minus is the hydroxide ions.
Let's define some terms from general chemistry
just to make sure this is clear and a reminder.
Ionization. It is the process of forming or splitting
of molecules to their respective cations and anions.
Usually in a molecule,
if atoms are bonded with high electronegative difference,
the bonded pair of electrons will be unequally
shared between 2 atoms which are bonded together.
In that the atom which is comparatively more electronegative,
will attract the bonded pair of electrons toward itself,
so that it is slightly negatively charged and atoms which is less electronegative,
attracts less electrons towards itself.
This will be the slightly positive charge.
These 2 oppositely charged ions have their own terms.
Cation, an atom that has a slight positive charge,
a positively charged ion.
Anion, an atom that has a negatively charged ion.
I had my own ways of remembering cation and anion,
which is positive, which is negative.
You can go for whatever you want.
I've had people say cat ions starts with
the word cat and cats are cute and it's a positive addition,
we have cats because we want them as pets,
so that is the positive 1 and can be associated, for example,
anarchy has a negative thing,
but that's already a subjective belief.
Therefore, however you remember whatever works for you, that's what you should go with.
Cation is an atom that is comparatively less
electronegative and will not attract shared pair of electrons towards itself,
hence it develops that slight positive charge and to simplify this,
it is a positively charged ion, a cation.
An anion which is an atom that is comparatively more electronegative,
will attract shared pair of electrons towards itself and it
develops and has a slight negative charge and in other words,
that is the negatively charged ion, the anion.
While the uncharged molecule H_2O contributes to the solvent properties of water,
as we covered in a previous lesson,
the small degree of ionization of water contributes to
these properties as well as needs to be taken into account.
Ionization of water is reversible and as in the case of all reversible reactions,
it can be described by an equilibrium constant.
When weak acids are dissolved in water,
they contribute the hydrogen atom H plus also known as the proton.
Weak bases consume H plus by becoming protonated,
transfer a proton to a molecule group of atom which forms a bond to this proton.
The total hydrogen ion H plus concentration from all sources can
be measured experimentally and is expressed as the pH of the solution.
To predict the state of ionization of solutes in water,
we must take into account
the relevant equilibrium constants for each ionization reaction.
Let's talk about the ionization of water and weak acids and bases dissolved in water.
Pure water is slightly ionized.
Water molecules have a slight tendency to
undergo reversible ionization to yield a proton,
a hydrogen ion, H plus,
and a hydroxide ion OH minus,
giving the equilibrium H_2O,
resulting in H plus plus OH minus proton,
the hydrogen ion, and OH minus the hydroxide ion and this is the water molecule.
This equilibrium means that it is going in a reversible fashion between
the 2 directions of this reaction when it is in the form of pure water.
Although we commonly show the dissociation product water as H plus,
free protons do not exist in solution.
Hydrogen formed in water are immediately hydrated to form hydronium ions H_3O plus.
Since it is important that you understand this concept, I will define this again.
Ionization of water, which in essence is self ionization of water or
autoionization of water is when a water molecule H_2O deprotonates,
loses a proton and forms a negatively charged ion,
an anion, OH minus hydroxide ion.
When water molecule H_2O deprotonates,
loses a proton H plus and forms a negatively charged ion,
an anion OH minus the hydroxide ion,
proton formed from the water molecule instantly protonates
another water molecule and forms a hydronium ion.
You have this right here what happens it instantly will find another water molecule.
You will have these molecules
because it's reversible so there's constantly shift back and forth,
so you'll have all these molecules and what will happen is that these will
associate and form this hydronium ion
so that actually what you have floating around is H_2O,
OH minus, and H_3O plus.
Since it's important you understand this concept,
I will define this again, ionization of water,
which in essence is self ionization of water or autoionization of
water is when a water molecule deprotonates, as you see here,
loses a proton or donates the proton and forms a negatively charged ion,
an anion OH minus, a hydroxide ion.
The proton formed from the water molecule instantly protonates
another water molecule and forms hydronium ion H_3O plus.
This shows the amphoteric nature of water and for,
think of amphibians that they live both on land and water so too amphoteric,
meaning it can be both an acid and a base.
It can act both as an acid or a base.
Again, the self ionization of water is
an ionization reaction in pure water or in an aqueous solution in which
a water molecule H_2O deprotonates to become a hydroxide ion OH minus.
The hydrogen nucleus H plus the proton immediately protonates
another water molecule to form hydronium H_3O plus.
What we see is 2 water molecules here,
hydrogen bonding between these 2 water molecules and it makes
the hydration of dissociating protons.
This is the 3 parallel lines representing the hydrogen bond.
It makes dissociation of protons virtually instantaneous so that this association,
this proton hops over you've got H_3O plus,
and you are left with OH minus the hydroxide ion.
Ionization of water can be measured by its electrical conductivity.
Pure water carries electrical current as H_3O plus
migrates towards the cathode and OH minus towards the anode.
Let's just step back and familiarize ourselves with the terms.
Both the cathode and anode are electrodes.
An electrode is a conductor that helps to establish
electrical contact with a non-metallic part of a circuit.
Electrodes consist of 2 major points called cathode and anode,
as you see here, which basically describes the direction of the flow of current.
A cathode can be considered an electrode from which
the current exits a polarized electrical device.
Conversely, anode can be described as an electrode from which
the current enters into the polarized electrical device.
The anode is the negative or reducing electrode that
releases electrons to the external circuit and oxidizes during
an electrochemical reaction while the cathode is the positive or oxidizing electrode that
acquires electrons from the external circuit
and is reduced during the electrochemical reaction.
The terms cathode and anode,
and this is an FYI for the history geeks,
these terms were finalized in 1834 by William Whewell,
who adapted the words from the Greek word Kathodos.
We're back to our Greek origin of words in science
and this in Greek means way down or descent.
The cathode is where the current exits way down or descent, Kathodos.
These terms were finalized by William after he had consulted with Michael Faraday,
that we probably know the term Faraday,
also from science and together they coined these terms.
Now, the movement of hydronium and hydroxide ions in the electrical field
is extremely fast compared to that of other ions such as sodium,
potassium, chloride, NA plus,
K plus, and Cl minus.
The high ionic mobility of hydronium and hydroxide
ions results from what is referred to as
proton hopping and can be seen in the figure below.
What you see here is a figure depicting proton hopping.
You have these water molecules,
you see the hydrogen bonding and you see the proton,
the H hopping as depicted by the red circle and this arrow over to
the next water molecule and that's in essence what we showed before in the individual.
This is the proton hopping over to this water molecule.
What you see here is the same idea in a chain of multiple water molecules.
No individual proton was very far through the bulk solution,
but a series of proton hops between
hydrogen bonded water molecules causes the net movement of a proton over
a long distance in a remarkably short time as H_3O plus a hydronium ion,
as seen in the upper left,
gives up a proton H_2O acquires 1 becoming H_3O plus, the hydronium ion.
Proton hopping is much faster than true diffusion.
This explains the remarkably high ionic mobility of proton ions, H plus ions,
compared with other monovalent cations such as NA plus or K plus,
sodium plus or potassium plus.
While H plus moves down this way, OH minus,
hydroxide also moves rapidly by proton hopping,
but in the opposite direction.
Now, as a result of this high ionic mobility of H plus,
acid-base reactions in aqueous solutions are exceptionally fast.
Because reversible ionization is crucial to the role of water in cellular function,
we must have a means of expressing the extent
of ionization of water in quantitative terms.
Let's review some properties of reversible chemical reactions to show this.
The position of equilibrium of any given chemical reaction
is given by its equilibrium constant K_eq for the reaction,
A plus B results in C plus D and being reversible,
you have the reactants,
you have the products and in this reversible reaction.
The equilibrium constant K_eq can be defined in terms of the concentrations of
reactants A and B and products C and D at equilibrium and is given by this equation,
K_eq equals the products over the reactants and as a reminder,
the brackets denote concentration.
The unit that results from this equation is molarity.
The equilibrium constant is fixed and characteristic for
any given chemical reaction at a specified temperature
meaning that any chemical reaction,
there is a known equilibrium constant at a specified temperature.
It defines the composition of
the final equilibrium mixture
regardless of the starting amounts of reactants and products.
Conversely, we can calculate the equilibrium constant for a given reaction at
a given temperature if the equilibrium concentrations
of all its reactants and products are known.
Also as we showed in previous section,
the standard free energy change Delta G is directly related
to the natural log ln of the equilibrium constant.
Knowing equilibrium concentration of reactants and
products of a chemical reaction, any chemical reaction,
we can calculate the equilibrium constant and
relate it to the free energy change and with this,
we completed this section covering ionized water and the equilibrium
constant of ionization of water and we explained the ionization of water.
We described how to measure the ionization of water,
and we related the equilibrium constant to the reactions covered.
This video covers the topic of ionization of water, specifically the equilibrium constant of ionization of water. By the end of the video, viewers will be able to explain the ionization of water, describe how to measure the ionization of water, and relate the equilibrium constant to the reactions covered. Ionization of water is when it is in the form of hydrogen ions, H plus, and hydroxide ions, OH minus. It is the process of forming or splitting of molecules to their respective cations and anions. Cation is an atom that is comparatively less electronegative and will not attract shared pair of electrons towards itself, hence it develops that slight positive charge. Anion is an atom that is comparatively more electronegative, will attract shared pair of electrons towards itself and it develops and has a slight negative charge. Ionization of water is reversible and can be described by an equilibrium constant. The total hydrogen ion H plus concentration from all sources can be measured experimentally and is expressed as the pH of the solution. To predict the state of ionization of solutes in water, we must take into account the relevant equilibrium constants for each ionization reaction. Pure water carries electrical current as H_3O plus migrates towards the cathode and OH minus towards the anode. Knowing equilibrium concentration of reactants and products of a chemical reaction, we can calculate the equilibrium constant and relate it to the free energy change.
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