Chemistry Acids and Bases Flashcards
A particularly common indicator is ___, which turns red in acidic solutions an blue in basic solutions
litmus paper
___ react with bases to form water and a salt
Non oxidizing acids react with metals to produce hydrogen gas
Aqueous base and acidic solutions can conduct electricity
acids
Arrhenius defined an acid as a species that produces H+ (a proton) in an ___ and a base as a species that produces OH- (a hydroxide ion) in an aqueous solution
aqueous solution
___ definitions of acids and bases fail to describe acidic and basic behavior in nonaqueous media
Arrhenius
A ___ is a species that donates protons, while a Bronsted-Lowry base is a species that accepts protons
NH3 can accept a proton but is not an Arrhenius base since it is not in aqueous solution
Bronsted-Lowry acid
Bronsted-Lowry acids and bases always occur in pairs, called ___. A conjugate acid is defined as the acid formed when a base gains a proton. Similarly, a conjugate base is formed when an acid losses a proton
conjugate acid-base pairs
H3O+ is the ___ of the base H2O and NO2- is the conjugate base of HNO2
H3O+ -> H2O + H+
HNO2 -> NO2- + H+
conjugate acid
Lewis defined an acid as an electron-pair acceptor and a ___ as an electron-pair donor. Every Arrhenius acid is a Bronsted-Lowry acid, every Bronsted-Lowry acid is also a Lewis acid (and likewise for bases)
base
The Lewis definition encompasses some ___ not included within the Bronsted-Lowry definition.
BCl3 and AlCl3 can each accept an electron pair and are therefore Lewis acids despite their inability to donate protons
species
Lewis ___ (and occasionally acids) are sometimes referred to as ligands
bases
Acids formed from \_\_\_ whose names end in -ide have the prefix hydro- and the ending -ic F- Fluoride HF Hydrofluoric acid Br- Bromide HBr Hydrobromic acid
anions
Acids formed from ___ are called oxyacids. If the anion ends in -ite (less oxygen), then the acid will end with -ous acid. If the anion ends in -ate (more oxygen), then the acid will end with -ic acid
oxyanions
ClO- \_\_\_ HClO Hypchlorous acid ClO2- Chlorite HClO2 Chlorous acid ClO3- Chlorate HClO3 Chloric acid ClO4- Perchlorate HClO4 Perchloric acid NO2- Nitrite HNO2 Nitrous acid NO3- Nitrate HN3 Nitric acid
Hypochlorite
pH = -log[H+]
pOH = -log[OH-]
In any aqueous solution , the H2O solvent ___ slightly in a process called autoionization
H2O (l) ->
dissociates
As [H+] goes up, the pH goes down (more ___); and as K sub a increases 9strong acid), pK sub a goes down
acidic
A method of estimating p-scale values:
If the ___ is written in proper scientific notation, it will look like n x 10 ^ -m, where n is a number between 1 an d10. The log of this product can be written as log(nx10^-m) = -m + log n, and the negative log is thus m - log n. Now, since n is a number between 1 and 10, its logarithm is a fraction between 0 an d1; thus, m - log n is between m-1 and m. Furthermore, the larger the n, the larger the log n, and therefore the closer the answer is to m -1
nonlogarithmic value
The strength of an acid or base is determined by its ability to ___ in aqueous solution. The more an acid or base dissociates in the presence of water molecules, the stronger it is
ionize
The ___ is inherently tied to the strength of its conjugate base. Most acids are neutral molecules that upon deprotonation leave a conjugate base that is an anion. Those conjugate bases that cannot stabilize the negative charge well quickly capture a proton to reform the acid molecule; thus, there are less dissociated acid molecules in solution and it is a weaker acid. Acids that have a conjugate base capable of stabilizing the negative charge, such as through resonance or induction, will have a greater degree of ionization
strength of an acid
For incredibly ___ and bases (near complete dissociation), the conjugate is so weak that it is practically inert
strong acids
Hence, in a 1 M ___ of NaOH, complete dissociation gives one mole of OH- ions per liter of solution
pH = 14 - (-log[OH-])=14 + log[1]
solution
Note that the [OH-] contributed by the ___ of H2O is considered to be negligible
autoionization
Given the pH of a 1 x 10^-8 M HCl solution
K sub w = [H+][OH-]
1 x 10^-14 = [x + 1 x 10^-8][x]
note that H+ from water and HCl are added together due to the ____
Solving for x gives x = 9.5 x 10^-8 so [H+ sub total] = [H+ from HCl + H+ from water] = 1.05 x 10^-7 M
and pH = -log(1.05 x 10^-7) = 6.98
The pH is slightly less than 7, as should be expected for a very dilute yet acidic solution
common ion effect
Strong Acids HClO4 (perchloric acid) HNO3 (nitric acid) H2SO4 (sulfuric acid) HCl (hydrochloric acid)
Strong Bases NaOH (sodium hydroxide) KOH (potassium hydroxide) Ca(OH)2 (calcium hydroxide) other soluble \_\_\_ of Group IA and IIA metals
hydroxides
For a ___:
HA (aq) + H2O (l) ->
weak acid
The ___, K sub a, is a specific type of K sub eq that measures the degree to which an acid dissociates by showing the ratio of concentrations of the products) the conjugate base and the H+ donated) to that o f the reactant (the original acid)
K sub a = [H3O+][A-]/[HA]
The weaker the acid , the smaller the K sub a. The strong vs weak acid designation is based on this value; strong acids have a K sub a > 1 while weak acids have K sub a < 1
acid dissociation constant
The ___ , K sub b, is a measure of the degree to which a base dissociates
base dissociation constant
The weaker the ___, the smaller its K sub b. Strong bases have a K sub b > 1 while weak bases have a K sub b < 1
K sub b = [B+][OH-]/[BOH]
base
To find the K sub a of the conugate acid HCO3-, the reaction with water must be considered:
HCO3 - (aq) + H2O (l) ->
dissociation constant
Calculate the ___ of H+ in a 2.0 M aqueous solution of acetic acid, CH3COOH (K sub a = 1.8 x 10^-5)
First write the equilibrium reaction:
CH3COOH (aq) -> H+(aq) + CH3COO- (aq)
K sub a = [H+][CH3COOO-]/[CH3COOH] = 1.8 x 10^-5
Because acetic acid is a weak acid, the concentration of CH3COOH at equilibrium is equal to tis initial concentration, 2.0M, less the amount dissociated, x. Likewise, [H+] = [CH3COO-] = x, since each molecule of CH3COOH dissociates into one [H+} ion and one CH3COO- ion. Thus, the equation can be rewritten as follows:
K sub a = [x][x]/[2.0-x] = 1.8 x 10^-5
We can approximate that 2.0-x is approximately 2.0 since acetic acid is a weak acid that only slightly dissociates in water, and x will be small.
Multiplying or dividing by small numbers can have large effects, but adding or subtracting small numbers is not statistically significant. The math can be made much simpler by ignoring x values that are added or subtracted from (comparably) large numbers:
K sub a = [x][x]/2.0
1.8 x 10^-5 = x^2/2
3.6x10^-5 = x^2
x = 6x10^-3 M
A rule of thumb is that the approximation is valid as long as x is less than 5 percent of the initial concentration
concentration
Acids and ___ may react with one another, forming a salt and (often, but not always) water in what is termed a neutralization reaction
bases
The ___ may precipitate out (of a neutralization reaction) or remain ionized in solution depending on its solubility and the amount produced
salt
The reverse ___, in which the salt ions react with water to give back the acid or base, is known as hydrolysis
reaction
Four combinations of strong and weak ___ and bases are possible:
1
strong acid + strong base: e.g., HCl + NaOH -> NaCl + H2O
2
strong acid + weak base: e.g., HCl + NH3 -> NH4Cl
3
weak acid + strong base: e.g., HClO + NaOH -> NaClO + H2O
4
weak acid + weak base: e.g., HClO + NH3 ->
acids
Weak acids have weak conjugate bases and vice versa. ___ have conjugate bases so weak that they are inert
strong acids
The products of a ___ between equal concentrations of a strong acid and a strong base are a salt and water
reaction
The ___ of a reaction between a strong acid and a weak base is also a salt, but usually no water is formed since weak bases are usually not hydroxides
product
Another way to consider this reaction is that the weak acid cation will react with the water ___, reforming the weak base
HCl (aq) + NH3 (aq) -> 7); the weak base anion (ClO- in our example will react with H2O solvent which leaves OH- to raise the pH
The pH of a solution containing a weak acid and a weak base depends on the relative strengths of the reactants. The acid HClO has a K sub a = 3.2 x 10^-8, and the base NH3 has a K sub b =1.8 x 10^-5. Thus, an aqueous solution of HClO and NH3 is basic, since the K sub a for HCLO is smaller than the K sub b for NH3, and therefore NH3 is the stronger reactant
solvent
The relative ___ or basicity of an aqueous solution is determined by the relative concentrations of acid and base equivalents
acidity
An ___ is equal to one mole of H+ (H3O+) ions; a base equivalent is equal to one mole of OH- ions
acid equivalent
Some acids are ___, that is, each mole of the acid or base liberates more than one acid or base equivalent
polyvalent
H2SO4 (aq) -> H+ (aq) + HSO4- (aq)
HSO4- (aq) ->
acid equivalents
The quantity of ___ is directly indicated by the solution’s normality (N) where N = Molarity x equivalents/mol. Because each mole of H3PO4 can liberate 3 moles (equivalents) of H+, a 2M H3PO4 solution would be 6N (6 normal)
acidic or basic capacity
Another useful measurement is ___. The equivalent weight is calculated by taking the molecular weight and dividing by the number of equivalents per mole. The gram molecular weight of H2SO4 is 98 g/mol. Because each mole liberates two acid equivalents, the gram equivalent weight of H2SO4 would be 98/2 = 49 g; that is the dissociation of 49 g of H2SO4 would release one acid equivalent. Common polyvalent acids include H2SO4, H3PO4, and H2CO3
equivalent weight
An amphoteric, or amphiprotic, species is one that can act either as an ___, depending on its chemical environment
acid or a base
In the Bronsted-Lowry sense, an amphoteric species can either gain or lose a proton.
When water reacts with a base, it behaves as an acid:
H2O +B ->
conjugate base
___ is a procedure used to determine the molarity of an acid or base
titration
Titration is accomplished by reacting a known ___ or a solution of unknown concentration with a known volume or a solution of known concentration. When the number of acid equivalents equals the number of base equivalents added, or vice versa, the equivalence point is reached
volume
While a strong acid/strong base titration will have an ___ at pH 7, the equivalence point need not always occur at pH 7. Also, when titrating polyprotic acids or bases, there are several equivalence points, as each acidic or basic species is titrated separately
equivalence point
The equivalence point in a ___ is estimated in two common ways: either by plotting pH (measured with a pH meter) of the solution as a function of added titrant on a graph of by watching for a color change of an added indicator
titration
Indicators are ___ or bases that have different colors in their undissociated and dissociated states. indicators are used in low concentrations and therefore do not significantly alter the equivalence point. The point at which the indicator actually changes color is not the equivalence point but is called the end point; this point is not significant mathematically but rather is a practical way to ensure the reaction has gone to completion.
If the titration is performed well, the volume difference (and therefore the error) between the end point and the equivalence point is small and may be corrected for or ignored
weak organic acids
A ___ consists of a mixture of a weak acid and its salt (which consists or its conjugate base and a cation) or a mixture of a weak base and its salt (which consists of its conjugate acid an an ion
buffer solution
Consider a ___ solution of acetic acid and sodium acetate:
CH3COOH -> H+ + CH3COO-
CH3COONa -> Na+ + CH3COO-
buffer
The Henderson-Hasselbalch equation is used to estimate the pH of a ___ in the buffer region where the concentrations of the species and its conjugate are present in approximately equal concentrations. For a weak acid buffer solution:
pH = pK sub a + log[conjugate base]/[weak acid]
Note that when [conjugate base] = [weak acid] (in titration, halfway to the equivalent point), the pH = pK sub a because log 1 = 0. Likewise, for a weak base buffer solution:
pOH = pK sub b + log[conjugate acid]/[weak base]
pOH = pK sub b when [conjugate acid] = [weak base]
solution
When a small amount of NaOH is added to the buffer, the OH- ions from the NaOH react with the acetic acid in the buffer solution such that:
CH3COOH + NaOH ->
buffer
Instead of the addition of a strong ___ (HCl), there is now a weak aci present (CH3COOH). Just as with the strong base, the pH shift will be quite small
acid
