Ch. 17 Chem
very weak acids _____ conjugate bases
strong conjugate bases
Percent ionization of weak acids decreases as...
tHE ACID (AND HYDROGEN ION) CONCENTRATION INCREASES..
The extent of dissociation of a weak acid is quantified by
the acid dissociation constant, Ka, which is the equilibrium constant for the ionization of the weak acid.
Strong acids have ___ conjugate bases
very weak conjugate bases
Explain the difference between a strong acid and a weak acid and list one example of each.
A strong acid completely ionizes in a solution. An example is HCl. A weak acid only partially ionizes in solution. An example is HF.
A weak acid solution is greater than, equal to, or less than, the initial acid concentration?
A weak acid solution is lower than the initial acid concentration
For oxyacids, acid strength increases with the
Electronegativity of the atoms bonded to the oxygen atom and also increases with the number of oxygen atoms in the molecule.
Which factors affect the relative acidity of oxyacid?
Factors affecting the ease with which the hydrogen will be donated (and therefore acidic) are the electronegativity of the element Y and the number of oxygen atoms attached to the element Y.
Most weak bases produce this through what?
Most weak bases produce hydroxide ions through the ionization of H2O. Base ionization constant, Kb, indicates the extent of ionization.
When is water produced in an acid-base neutralization reaction?
Only produced in neutralization reactions that involve a strong base
What is the Bronsted-Lowry definition of an acid?
A Bronsted-Lowry acid is a proton (H⁺) donor.
What is a Bronsted-Lowry definition of a base?
A Bronsted-Lowry base is a proton (H⁺) acceptor.
In a strong acid solution, the hydrogen ion concentration is greater than, equal to, or less than the initial concentration of the acid?
Strong acid solution equals the initial concentration of the acid.
What is a general characteristic of a Lewis acid? Of a Lewis base?
A Lewis acid has an empty orbita (or can rearrange electrons to create an empty orbital) that can accept an electron pair. A Lewis base has a lone pair of electrons that it can donate to the Lewis acid.
What is the Lewis definition of an acid? Of a base?
A Lewis acid is an electron pair acceptor. A Lewis base is an electron pair donor.
what is a carboxylic acid? Give an example.
A carboxylic acid is an organic acid that contains the following group of atoms: HOCO. Carboxylic acids are often found in substances derived from living organisms. Examples include citric acid, malic acid, and acetic acid.
Cations that are the conjugate acids of weak bases...? These cations are conjugate acids of what weak bases? NH₄⁺ C₂H₅NH₃⁺ CH₃NH₃⁺
A cation can be formed from any nonionic weak base by adding H to it's formula. NH₃ C₂H₅NH₂ CH₃NH₂
What kinds of cations act as weak acids? List examples.
A cation that is the conjugate acid of a weak base such as NH₄⁺ is a weak acid. Small highly charged metal cations such as Al³⁺ and Fe³⁺ form weakly acidic solutions.
What is a conjugate acid-base pair? Provide an example.
A conjugate acid-base pair consists of two substances related to each other by the transfer of a proton in the reaction: NH₃ (aq) + H₂O (l) ⇌ NH₄⁺ (aq) + OH⁻ (aq) the conjugate pairs are NH₃/NH₄⁺ and H₂O/OH⁻
Define poH. What pOH range is considered acidic? Basic? Neutral?
We define pH as pOH= -log[OH⁻]. An acidic solutio has poH>7, basic solution has a pOH<7, and a neutral solution has pOH=7
What are the diprotic and triprotic acids? list an example of each.
A diprotic acid contains two ionizable protons. An example is H₂SO₄. Triprotic acid contains three ionizable protons. An example is H₃PO₄.
Why is there more than one definition of acid-base behavior? Which definition is the right one?
According to Huheey, "Differences between the various acid-base concepts are not concerned with which is right, but which is most convenient to use in a particular situation." No single correct definition; we use the definition that is best for a particular situation.
What are the general physical and chemical properties of acid?
Acids have the following general properties: a sour taste, ability to dissolve many metals, the ability to turn blue litmus paper red, and the ability to neutralize bases.
Describe amphoteric behavior and give an example.
Amphoteric substances can act as acids or bases depending on the circumstances. Some amphoteric substances are H₂O and NH₃.
What is the Arrhenius definition of an acid? Of a base?
An Arrhenius acid is a substance that produces H⁺ in aqueous solution. An Arrhenius base is a substance that produces OH⁻ in aqueous solution.
Define the acid ionization constant and explain its significance.
An acid ionization constant (K_a) is the equilibrium constant for the ionization reaction of a weak acid. The smaller the acid ionization constant, the weaker the acid.
how can you determine if an anion will act as a weak base? Write a generic equation showing the reaction by which an anion, A⁻, acts as a weak base.
An anion that is the conjugate base of a weak acid is itself a weak base. A⁻ (aq) + H₂O (l) ⇌ HA (aq) + OH⁻ (aq) An anion that is the conjugate base of a strong acid is pH-neutral.
In a weak acid solution, the hydrogen ion concentration can be determined by solving what?
An equilibrium problem
What is the relationship between the acid ionization constant for a weak acid (Ka) and the base ionization constant for its conjugate base (Kb)?
At 25°C, the product of Ka for an acid and Kb for it's conjugate base is Ka∙Kb=Kw=1.0∙10⁻¹⁴
Write a generic equation showing how a weak base ionizes water.
B (aq)+ H₂O (l) ⇌ BH⁺ (aq) + OH⁻ (aq)
What are the general physical and chemical properties of bases?
Bases have the following general properties: a bitter taste, slippery feel, the ability to turn red litmus paper blue, and ability to neutralize acids.
What happens to the [OH⁻] of a solution when the [H₃O⁺] is increased? What happens when it decreases?
Because Kw= 1.0∙10⁻¹⁴, the concentration of [H₃O⁺] times the concentration of OH⁻ is always 1.0∙10⁻¹⁴ , therefore, if [H₃O⁺] increases, [OH⁻] decreases and vis versa.
In mixtures of two acids with large Ka differences, the concentration of hydrogen ions can be determined how?
By considering only the stronger of the two acids.
For a weak diprotic acid H₂X, what is the relationship between X² and Ka₂? Under what conditions does this relationship exist?
For a weak diprotic acid, X²⁻= Ka₂. This result is general for all diprotic acids in which the x is smaall approximation is valid.
For binary acid, H-Y, which factors affect the relative ease with which the acid ionizes?
For an H-Y binary acid, the factors affecting the ease with which this hydrogen will be donated are the polarity of the bond and the strength of the bond.
When calculating the H30+ for a polyprotic acid, the second ionization step can often be neglected. Explain why this statement is valid.
For most polyprotic acids, Ka¹ is much larger than Ka₂. Therefore, the amount of H₃O⁺ contributed by the first ionization step is much larger than that contributed by the second or third ionization step. In addition, the production of H₃O⁺ by the first step inhibits addition production of H₃O⁺ by the second step because of Le Chatelier's principle.
In an acidic solution, the concnetration of Hydrogen ions is always...
Greater than the concentration of hydroxide ions. H₃O⁺ multiplied b y OH⁻ is always constant at a constant temperature.
The Arrhenius definition of acids and bases states that
In an aqueous solution, an acid PRODUCES hydrogen ions and a base PRODUCES hydroxide ions.
Write an equation for the autoionization of water and the expression for the ion product constant for water (K_w). What is the value of K_w at 25 °C?
The autoionization of water is H₂O (l) + H₂O (l) ⇌ H₃O⁺ (aq) + OH⁻ (aq) and has the ion product of water K_w = [H₃O⁺][OH⁻] It can also be written as: H₂O (l) ⇌ H₃O⁺ (aq) + OH⁻ (aq) , and the ion product of water is K_w= [H⁺][OH⁻] at 25 °C, k_w= 1.0∙10⁻¹⁴
What is a hydronium ion? Does H⁺ exist in solution by itself?
The hydronium ion is H₃O⁺. In water, H⁺ ions always associate with H₂o molecules to form hydronim ions and other associated species with the general formula H(H₂O)_n⁺
What is the percent ionization of an acid? Explain what happens to the percent ionizaion of a weak acid as a function of the concentration of a weak acid solution.
The perceent ionization is defined as percent ionization = concentration of ionized acid/ initial concentration of acid x100. The percent ionization of a weak acid decreases with the increasing concentration of acid.
When calculating [H₃O⁺] for weak acid solutions, we can often use the x is small approximation. Explain the nature of this approximation and why it is valid.
The x is small approximation is used when the equilibrium constant is relatively small and the initial concentration is relatively large. We make the assumption that x is small compared to the initial concentration. If the assumption is valid, x is <5% of the initial concentration.
How to classify acids as strong or weak?
There are 7 strong acids which are: Hydrochloric acid--HCl, Hydrobromic acid--HBr, Hydroiodic acid--HI, Chloric acid--HClO3, Perchloric acid--HClO4, Nitric acid --HNO3, Sulfuric acid--H2SO4, All others are weak acids.
How to classify bases as strong or weak?
There are 8 strong bases: Lithium hydroxide LiOH Sodium hydroxide NaOH Potassium hydroxide KOH Rubidium hydroxide RbOH Cesium hydroxide CsOH Calcium hydroxide Ca(OH)2 Strontium hydroxide Sr(OH)2 Barium hydroxide Ba(OH)2 All other bases are weak.
In the opening section of this chapter, we see that in the batman comic book series, batman treats a strong acid burn with a strong base. What is problematic about this treatment?
There are two problems with this treatment. First, neutralizing reaction between a strong acid and a strong base is highly exothermic. Second, strong bases are themselves caustic to the skin. Both would burn skin. Standard treatment for spilling concentrated acid is to rinse with large amounts of H₂O
In most solutions containing a strong or weak acid, the autoionization of water can be neglected when calculation [H₃O⁺]. Explain why this statement is valid.
We can neglect the contribution of autoionization of water to the H₃O⁺ concentration in a solution of a strong or weak acid because it is negligible compared to the concentration of H₃O⁺ ions generated from the dissociation of the acid. Even the weakest of the weak acids has an ionization constant that is four orders of magnitude larger than that of water.
Define pH. What pH range is considered acidic? Basic? Neutral?
We define pH as pH= -log[H₃O⁺]. An acidic solution has a pH < 7 a basic solution has a pOH<7, and a neutral solution has a pOH=7
The Bronsted-Lowry definition of acids and bases state that
an acid is a proton (a hydrogen ion) donor and a base is a proton acceptor. Two substances related by the TRANSFER of a proton are the conjugate acid-base pair.
Binary acids, the acid strength decreases with... increases with...?
increasing bond energy and increases with increasing bond polarity
Cations that are the counterions of strong bases are themselves...? What do these cations act as a counterion for: Na⁺, K⁺, Ca⁺
pH Neutral. NaOH, KOH, Ca(OH)₂
There are two types of logarithmic acid-base scales, what are they?
pH and pOH. At 25° C, the sum of pH and pOH is always 14.