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According to Arrhenius, define acids and bases
- acids: substances that dissociate in water to produce hydrogen ions
- bases: substances that dissociate in water to yield hydroxide ions
We refer to Arrhenius reactions as __.
What are the limitations to Arrhenius reactions?
- 1) restricted to aqueous solutions
- 2) doesn't account for the basicity of substances like ammoinia that don't contain OH groups
Bronsted-Lowry acids and bases
- acid is any substance that can transfer a proton to another substance (proton donors)
- base is a substance that can accept a proton (proton acceptors)
Acid-base reactions based on Bronsted-Lowry are __.
proton transfer reactions
What are the conjugate acid base pairs?
Chemical species whose formulas differ only by oe proton
The products of a Bronsted Lowry acid base reaction, BH+ and A- are __. The species BH+ produced when the base B accepts a proton from HA can itself donate a proton back to A-, meaning it is a __.
Similarly, the species A- produced when HA loses a proton can itself accept a proton back from BH+, meaning it is a __.
- acids and bases
- Bronsted-Lowry acid
- Bronsted-Lowry base
In the reaction:
HA + B --> BH+ and A-,
what are the conjugate bases?
When a Bronsted-Lowry acid HA dissolves in water, it reacts reersibly with water in an __. The acid transfers a proton to the __, which acts as a __ The products are th __ and __.
- acid-dissociation equilibrium
- base (a proton acceptor)
- hydronim ion
For a molecule or ion to accept a proton, it must have at least __.
one unshared pair of elections that it can use for bonding to the proton
True or False:
Some Bronsted-Lowry bases have one or ore lone pairs of electrons.
When beginning with equal concentrations of reactants and products, what?
What does this mean?
- the product is always transferred to the stronger base.
- this means that the direction of reaction to reach equilibrium is proton transfer fro the stronger acid to the stronger base to give the weaker acid and the weaker base
one that almsot completely dissociates in water; strong electroylye; acid-dissociation equilibrium of a strong acid lies nearly 100% to the right and the solution contains mostly H3O+ and A-
Typical strong acids are:
Strong acids have __, such as ClO4-, cl-, Br-, I-, NO3-, and HSO4-, which have negligible tendency to combine with a proton in a weak solution, and are much weaker bases than H2O.
wek conjugate bases
In terms of weak acids, what happens?
a small fraction of the weak acid molecuels transfer a proton to water, and the solution contains mainly undissociated HA molecules along with small amounts of H3O+ and the conjugate base A-
Typical weak acids?
HF, acetic acid, HNO2
In terms of weak acids, the acid has practically no tendency to transfer a proton to water nad the __ lies essentially __.
- acid-dissociation equilibrium
- 100% to the left
Because H+ is too reactive by itself, what happens?
it bonds with H2O to form H3O+
The hydronium ion can also do what with additional water molecules to give what?
- hydrogen bond
- higher hydrates such as H5O2, etc.
What is one of the most important properties of water?
to act both as acid and base
Called the __, this reaction is characterized by the equilibrium equation __, where the equilibrium constant kw is called the __.
- dissociation of water
- ion-product constant for water
dissociation ofw ater
2 H2O (l) <--> H3O+ + OH-
ion-product constant for water
Why is water concentration omitted from the equilibrium constant?
becuase it is a pure liquid
There are two important aspects of the dynamic equilibrium in the dissociation of water:
- 1) the forward nad reverse reactions are rapid (protons transfer quickly from one species to the next)
- 2) the position of the equilibrium lies far to the left: at any given instant, only a tiny fraction of the water molecules are dissociated into H3O+ and OH- ions; the vast majority of hte H2O molecules are dissociated
What occurs in very dilute solutions?
the water is almost a pure liquid and the product of the H3O+ and OH- concentrations is always 1.0 x 10^-14 in any aqueous solution
What is kw affected by?
like all equilibrium constants, it is affected by temperature and the H3O+ ad OH- concentrations in neutral aqueous solutions at temps other than 25 degrees Celsiuc
pH refers to what?
the power of ten (the exponent) used to express the molar H3O_ concentration; it is the negative base-10 log of hte molar h3O+ ion concentration
Explain sig figs in logs?
the only sig figs in a log are the digits to the right of hte decimal point; the number on the left of the decimal is the exact number related to the integral power of 10 in the exponential equation
What can pH also be determined using?
an acid-base indicator, which exhibit pH dependent color changes because they are weak acids nad have different colors in their acid and conjugate base forms
device tha tmaeasures the pH-dependent electrical potential of the test solution
commercially available mixture of indicators that exhiit various colors depending on the pH
Because strong monoprotic acids dissociate 100% in water, the H3O+ and A- concentrations rae __
equalt o the initial concentration of the acid and the concentration of undissociated HA molecules is zero
Most familiar examples of strong bases are __.
alkali metal hydroxides (like NaOH, KOH, etc.)
The __ are also strong, but not as soluble.
alkaline earth metal hydroxides
__ are even stronger bases htan the corresponding __ because the __ ion is a stronger base than __.
- alkaline earth oxides
- oxide ion (O2-)
True or False:
O2- cant exist in aqueous solutons because it is immediately and completely protonated by water, yielding H+ ions
- O2- cant exist in aqueous solutons because it is immediately and completely protonated by water, yielding H+ OH- ions
True or False
weak acid= dilute soluton of a strong acid
- weak acid is not equal to a dilute...
- strong acids completely dissociate; weak only partly
The equilibrium constant for a dissociation reaction, denoted __,is called the __.
What is it?
- acid-dissociation constant
- Ka= [H3O+][A-]/[HA]
pKa does what as Ka increases?
The larger the value of Ka, the __.
stronger the acid
Strong acids, like HCL, have Ka values that are much __ and pKa values that are __.
Once ka for a weak acid is measured, it can be used to __
calculate equilibrium concentrations and the pH in a solutoin of the acid
The proton-transfer reaction that proceeds farther to the right--the one that has the __-- is called the __.
- larger equilibrium constnat
- principal reaction
Any other proton transfer reactions are called __.
the concentration of the acid that dissociaties divided by the inital concetration of the acid times 100%
How many OH- does O2- produce?
Acids that contain more than one dissociable proton are called __.
if they have more than one ka value, what is the general order?
- it's more difficult to remove a proton from a more negative ion
__ acid solutions contain a mix of acids and __ in the case of a __ acid. Because H2A is the strongest, the principal reaction is __.
- dissociaiton of H2A and essentially all the H30_ in the soluton comes from the first dissociation step
Weak bases do what?
accept a proton from water to give the conjugate acid of the base and OH- ions
The equilibrium reaction of any base B with water is characterized by an equilibrium equation similar in form to that for the dissociation of a weak acid. The equilibrium constant is called hte __.
- base-dissociation constant, Kb
- Kb= ([BH+][OH-])/[B]
Many weak bases are organic compounds called __, derivatives of ammonia in which one or more hydrogen atoms are replaced by an organic, carbon-based group like a methyl group.
The basicity of an amine is due to what?
the lone pair of electrons on the nitrogen atom, which can be used for bonding to a proton
How are Ka and Kb related?
the equilibrium constant for the net reaction equals the product of hte equilibrium constants for the reactions added
True or False:
For any conjugate acid-base pair, the product of the acid dissociation constant for the acid and the base dissociation constant for the base alwys equals the ion-product constant for water
As the strength of an acid increases (larger Ka), what happens to Kb
strength of its conjugate base decresees (smaller kb)