Chapter 16: Acids and Bases Flashcards
What is the Arrhenius definition of an acid?
A substance that produces H+ ions in aqueous solution.
What is the Arrhenius definition of a base?
A substance that produces OH- ions in aqueous solution.
What does the strength of an acid or a base depend on?
The extent of the electrolyte’s dissociation into its component ions.
What is a strong acid?
An acid that completely dissociates (ionizes) in solution.
What is a weak acid?
An acid that partially dissociates (ionizes) in solution.
What is a strong base?
A base that completely dissociates (ionizes) in solution.
What is a weak base?
A base that partially dissociates (ionizes) in solution.
What is the Bronsted-Lowry definition of an acid?
A proton (H+) donor.
What is the Bronsted-Lowry definition of a base?
A proton (H+) acceptor.
What are amphoteric substances?
Substances that can act as acids or bases.
What is a conjugate acid-base pair?
Two substances related to each other by the transfer of a proton.
What is a conjugate acid?
Any base to which a proton has been added.
What is a conjugate base?
Any acid from which a proton has been removed.
What are the factors of a molecule that affect the ease with which a hydrogen is donated (and therefore makes the molecule acidic)?
- The polarity of the bond
- The strength of the bond
In order for HY to be acidic, the H–Y bond must be what?
The H–Y bond must be polarized with the hydrogen atom as the positive pole because hydrogen must be lost from the acid as a positively charged ion. A partial positive charge on the hydrogen atom facilitates its loss.
Why isn’t LiH acidic?
It is ionic with the negative charge on the hydrogen atom. (H is more electronegative than Li)
Why isn’t the C–H bond acidic?
It is virtually nonpolar because the electronegativities of carbon and hydrogen are similar; therefore, C–H is not acidic.
Why is the H–F bond acidic?
The H–F bond is polar with the positive charge on the hydrogen atom.
How does the strength of the H–Y bond relate to the strength of an acid? Why?
The stronger the H–Y bond, the weaker the acid. The more tightly the hydrogen atom is held, the less likely it is to come off.
Why are HCl and HBr strong acids but HF is not?
HCl and HBr have weaker bonds. HF, in contrast, has a stronger bond and is therefore a weak acid, despite the greater bond polarity of HF.
In oxyacids, what determines the ease with which the H is donated?
The ease with which the H is donated is related to the strength and polarity of the H–O bond. The factors affecting the strength and polarity of the bond are the electronegativity of the element Y and the number of oxygen atoms attached to the element Y.
As Y becomes more electronegative, how does this affect the H–O bond of an oxyacid?
The more electronegative the element Y is, the more it weakens and polarizes the H–O bond and the more acidic the oxyacid is.
How does the number of oxygen atoms bonded to Y affect the strength of the acid?
The greater the number of oxygen atoms bonded to Y, the stronger the acid.
What are the six strong acids given in the book?
- HCl (hydrochloric acid)
- HBr (hydrobromic acid)
- HI (hydroiodic acid)
- HNO3 (nitric acid)
- HClO4 (perchloric acid)
- H2SO4 (sulfuric acid)
Why is HCl a strong acid but HF is not?
The strength of the HF bond relative to the HCl bond makes HF less likely to ionize in solution than HCl.
What is the acid ionization constant (Ka)?
The equilibrium constant for the ionization reaction of the weak acid in water. It is a way to quantify the relative strength of a weak acid.
What is the autoionization of water?
When water acts as an acid and a base with itself. Given by the reaction: H2O <=> H+ + OH-
What is the ion product constant of water?
[H+][OH-] = 10^-14 at 25˚ C
How is pH defined?
pH is the negative of the log of the hydronium ion concentration. pH = -log[H3O+]
How is pOH defined?
pOH = -log[OH-]
How are pH and pOH related to each other?
They add to 14.00 at 25˚ C.
How is pKa defined?
pKa = -log(Ka)
How is pKa used to quantify the strength of an acid?
The smaller the pKa, the stronger the acid.
In a solution containing a strong or weak acid, what are the two potential sources of H3O+?
- The ionization of the acid
- The autoionization of water
What is the percent ionization of a weak acid?
The ratio of the ionized acid concentration to the initial acid concentration, multiplied by 100%.
How is the equilibrium H3O+ concentration of a weak acid related to its initial concentration?
The equilibrium H+ concentration increases with increasing initial concentration of the acid.
How is the percent ionization of a weak acid related to its concentration?
The percent ionization of a weak acid decreases with increasing concentration of the acid.
When a strong acid and a weak acid are in solution, what effect does the strong acid have on the weak acid?
The H+ formed by the strong acid suppresses the formation of additional H+ by the weak acid or the autoionization of water.
What is the base ionization constant (Kb)?
The extent of ionization of a weak base in solution. Given by: Kb = [BH+][OH-]/[B]
An anion that is the conjugate base of a weak acid is what?
A weak base.
An anion that is the conjugate base of a strong acid is what?
pH-neutral (forms solutions that are neither acidic nor basic)
How is the strength of an acid related to the strength of its conjugate base?
The weaker the acid, the stronger the conjugate base.
pKa + pKb = ?
14
How do anions and cations factor into acid-base reactions?
Anions can sometimes act as weak bases. Cation can sometimes act as weak acids.
In general, cations that are the counterions of strong bases are what?
pH-neutral. 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.
In general, a cation that is the conjugate acid of a weak base is what?
A weak acid.
What effect do small, highly charged metal cations have in solution?
Cations such as Al3+ and Fe3+ form weakly acidic solutions.
What is the definition of a Lewis acid?
An electron pair acceptor.
What is the definition of a Lewis base?
An electron pair donor.
