Ch 17: Acids and Bases Flashcards
A strong acid implies ______ ________ between the H+ and A-, resulting in complete ionization.
A weak acid implies a ______ attraction between the H+ and A-, resulting in only partial ionization.
weak attraction
strong
What is meant by an “amphoteric species”?
That it can act either as an acid or a base.
p. 740
We define pH as…
And pOH as….
…the negative of the logarithm of the hydronium ion concentration:
pH = -log[H3O+]
pOH = -log[OH-]
p. 742-743
Since the pH scale is based on logarithmic function, an increase of 1 on the pH scale corresponds to….
…..a factor of 10 decrease in [H3O+].
p. 743
The log of a number is….
…the exponent to which 10 must be raised to obtain that number.
log 101 = 1
log 10-1 = -1
It is possible for concentrated acid solutions to have a ________ pH.
negative
We can use the dissociation constant for water (KW; also called the ion product constant for water) to find the [OH-] concentration when we are given [H3O+] (or vice versa) since this mathematical relationship exists:
KW = [OH-] [H3O+] = 1.0 x 10-14
p. 741
What is the mathematical relationship between pH and pOH?
pH + pOH = 14.00
p. 744
How can we calculate the pKa from the Ka value? (or vice versa)
pKa = -log [Ka]
Because strong acids, by definition, completely ionize in solution and because we can usually ignore the contribution of the autoionization of water, the concentration of H3O+ is a strong acid solution is _____ to the ____________ of the strong acid.
For example, a 0.10 M HCl solution has an [H3O+] concentration of 0.10 M and a pH of 1.00
0.10 M HCl → [H3O+] → pH = -log(0.10) = 1.00
equal to the concentration
We can define the percent ionization of a weak acid using the equation…
Percent ionization = (concentration of ionized acid/ initial concentration of acid) x 100% = [H3O+] equil / [HA]initial x 100%
The conjugate acid is a base that has….
….accepted a H+ ion.
In general, anions tend to form either ______ or neutral solutions, while cations tend to form either ______ or neutral solutions.
basic
acidic
cations - acidic or neutral
anions – basic or neutral
Remember there can be only one a in each pair, so cations must be acidic, while anions must be basic.
An anion that is the conjugate base of a weak acid is itself, a ____ ____.
weak base
An anion that is the conjugate base of a strong acid, is _________, and forms solutions that are neither acidic nor basic.
pH-neutral
In general, the weaker the acid, the stronger the conjugate base. In contrast, the conjugate base of a strong acid, such as Cl−, does not act as a base because this reaction lies far to the _____. The stronger an acid, the weaker its _________ ____.
right
conjugate base
Is NO3- a weak base or pH neutral?
Since this is the conjugate base of strong acid, (nitric acid), it is therefore, pH-neutral.
Is NO2- a weak base or pH neutral?
Since Is NO2- is the conjugate base of a weak acid (nitrous acid), it is a weak base.
What is the mathematical relationship between Ka and Kb?
What about in terms of using the log function?
Ka x Kb = Kw = 1.0 x 10-14
log (Ka x Kb) = log Kw
log Ka + log Kb = log Kw
log Ka + log Kb = log 10-14 = -14
-log Ka - log Kb = 14
Since -log K = pK → pKa + pKb = 14
In general, cations that are the counterions of _____ _____ are themselves pH-neutral (they form solutions that are neither acidic nor basic). For example, Na+, K+, and Ca2+ are the counterions of the strong bases NaOH, KOH, and Ca(OH)2 and are therefore themselves pH-neutral.
Although these counterions interact with water molecules via ion–dipole forces, they do not ionize water and they do not contribute to the acidity or basicity of the solution.
strong bases
In general, a cation that is the conjugate acid of a weak base is a ____ ____.
weak acid
Small, highly charged metal cations such as Al3+ and Fe3+ form weakly ______ solutions. For example, when Al3+ is dissolved in water, it becomes hydrated according to the equation:
In effect, the binding of a water molecule to a cation like this makes the water more acidic.
Neither the alkali metal cations nor the alkaline earth metal cations ionize water in this way, but the cations of many other metals do. The smaller and more ______ ________ the cation, the more acidic its behavior.
acidic
highly charged
Is the cation Cr3+ a weak acid, or pH-neutral?
Cr3+ is a small, highly charged, metal cation, and is therefore, a weak acid.
Salts in which neither the cation nor the anion acts as an acid or a base form pH-neutral solutions. A salt in which the cation is the counterion of a strong base and in which the anion is the conjugate base of strong acid forms a _______ ________.
neutral solution
Examples include NaCl, Ca(NO3)2, and KBr.
Salts in which the cation does not act as an acid and the anion acts as a base form _____ ________. A salt in which the cation is the counterion of a strong base and in which the anion is the conjugate base of a weak acid forms a basic solution.
basic solutions
Examples include: NaF, Ca(C2H3O2)2 (calcium acetate), and KNO2 (potassium nitrite)
Salts in which the cation acts as an acid and the anion does not act as a base form _____ solutions. A salt in which the cation is either the conjugate acid of a weak base or a small, highly charged metal ion and in which the anion is the conjugate base of strong acid forms an acidic solution.
acidic
Salts in which the cation acts as an acid and the anion acts as a base form solutions in which the pH depends on the relative strengths of the acid and the base. A salt in which the cation is either the conjugate acid of a weak base or a small, highly charged metal ion and in which the anion is the conjugate base of a weak acid forms a solution in which the pH depends on the relative strengths of the acid and base.
The neutral cations are the conjugate acids of the…
….strong bases.
The neutral anions are the conjugate bases of the…
….7 strong acids.
Ka2 is always smaller than Ka1 because…
….the first proton separates more easily from a neutral molecule, but the second one separates from an anion. The negatively charged anion, holds the positively charged proton more tightly, making it difficult to remove, and resulting in a smaller value of Ka.
We can treat most polyprotic acid solutions as if the first ionization was the only one that contributes to the H3O+ concentration. A major exception is a dilute solution of ________ acid. See Example 17.18.
sulfuric acid
Why is does HF have an “acidic proton”, while LiH does not?
LiH is an ionic compound, with the negative charge on the H atom, therefore, it cannot be acidic.
In contrast, the H-F bond is polar with the positive charge in the H atom. This is what makes HF an acid. That partial positive charge makes it easier for the H to be lost as an H+ ion.
What is the trend in bond strength and polarity of the hydrides of group 6A and 7A?
2 different reasons: from Left to RIGHT, they become more acidic because the H-Y bond becomes more polar.
From top to BOTTOM, they become more acidic because the H-Y bond becomes weaker.
Which acid has the largest Ka?
HClO2
HBrO2
HIO2
For oxyacids, acid strength __________ with increasing electronegativity of the atom bonded to the oxygen atoms.
HClO2
INCREASES
The weaker the acid (the smaller the Ka), the ________ the conjugate base.
stronger
When Mn3+ is dissolved in water, it becomes hydrated. The ________ form of the ion then acts as a Brønsted-Lowry acid (i.e., it donates a proton to water):
Mn(H2O)63+(aq) + H2O(l) ⇌ Mn(H2O)5(OH)2+(aq) + H3O+(aq)
You may also show the reaction without ligands as:
Mn3+(aq) + 2 H2O (l) ⇌ MnOH2+(aq) + H3O+(aq)
hydrated
What is the Arrhenius definition of an acid/base?
An acid is a substance that produces H+ ions in an aqueous solution. A base is a substance that produces OH− ions in aqueous solution.
p. 735
What are the Bronsted-Lowry definitions of an acid or a base?
An acid is a proton (H+) donor.
A base is a proton acceptor.
How would you find the pH of a solution that is 4.8×10−2 M HClO4, and 4.5×10−2 M in HCl?
Both are strong acids, which dissociate completely in solution. So, the total concentration of H3O+ is the sum of H3O+ concentration of each acid:
pH = −log ([HI]+[HClO4]) = −log (4.8×10−2 + 4.5×10−2) = 1.03
