Ch 10 - Acids and Bases Flashcards
What are arrhenius acids?
dissociate to produce an excess of hydrogen ions in solution
What are arrhenius bases?
dissociate to produce an excess of hydroxide ions in solution
What are Bronsted-Lowry acids/bases?
- acids: species that can donate hydrogen ions
- bases: species that can accept hydrogen ions
revolves around protons
What are Lewis acids/bases?
- acids: electron pair acceptors
- bases: electron pair donors
revolves around electrons
How do arrhenius, Bronsted-Lowry, and Lewis acids and bases compare?
- all Arrhenius acids and bases are Bronsted-Lowry acids and bases, and all Bronsted-Lowry acids and bases are Lewis acids and bases
- however, the reverse is not necessarily true
- not all Lewis are Bronsted and not all Bronsted are Arrhenius
What is the difference between amphoteric and amphiprotic?
- amphoteric: can behave as an acid or base
- amphiprotic: amphoteric species that specifically can behave as a Bronsted acid/base
- water, amino acids, and partially deprotonated polyprotic acids such as bicarbonate and bisulfate are common examples of both
- metal oxides and hydroxides are amphoteric by not amphiprotic (do not give off protons)
Why is water special in acid/bases?
- classic example of an amphoteric, amphiprotic species
- it can accept a hydrogen ion to become hydronium ion or it can donate a hydrogen ion to become a hydroxide ion
What is the water dissociation constant (Kw)?
Kw = [H3O+][OH-] = 10^-14 at 298 K
Kw = Ka x Kb
- only affected by changes in temperature, in turn, change the significance of the pH scale
How are pH and pOH calculated?
can be calculated given the concentrations of H3O+ and OH- ions
pH = -log[H+] = log(1/[H+])
pOH = -log[OH-] = log (1/[OH-])
- in aqueous solution, pH + pOH = 14
What is the difference between strong and weak acids/bases?
- strong completely dissociate in solution
- weak do not completely dissociate in solution and have corresponding dissociation constants (Ka and Kb)
What are the conjugates in Bronsted-Lowry acids/bases?
- acids have conjugate bases that are formed when the acid is deprotonated
- bases have conjugate acids that are formed when the base is protonated
- strong acids/bases have very weak (inert) conjugates
- weak acids/bases have weak conjugates
- removing a proton from a molecule produces the conjugate base and adding a proton produces the conjugate acid
What do neutralization reactions form?
salts and (sometimes) water HA + BOH --> BA + H2O
What is an equivalent?
one mole of the species of interest
What is normality in acid-base chemistry?
the concentration of acid or base equivalents in solution
What are polyvalent acids/bases?
- those that can donate or accept multiple electrons
- the normality of a solution containing a polyvalent species is the molarity of the acid or base times the number of protons it can donate or accept
What are titrations used for?
to determine the concentration of a known reactant in a solution
What is a titrant and a titrand?
- titrant: has a known concentration and is added slowly to the titrand to reach the equivalence point
- titrand: an unknown concentration but a known volume
What is the half-equivalence point?
the midpoint of the buffering region, in which half of the titrant has been protonated (or deprotonated); thus, [HA] = [A-] and a buffer is formed
What is the equivalent point?
- indicated by the steepest slope in a titration curve
- reached when the number of acid equivalents in the original solution equals the number of base equivalents added or vice versa
What are the pH of equivalent points of strong/weak acids/bases titrations?
- strong acids and strong base titrations have equivalence points at pH=7
- weak acid and strong base titrations have equivalence points at pH>7
- strong acid and weak base titrations have equivalence points at pH<7
- weak acid and weak base titrations can have equivalence points above or below 7, depending on the relative strength of the acid and base
What are indicators?
weak acids or bases that display different colors in the protonated and deprotonated forms
- the indicator chosen for a titration should have a pKa close to the pH of the expected equivalent point
What is the endpoint of a titration?
when the indicator reaches its final color
What are buffer solutions?
consist of a mixture of a weak acid and its conjugate sat or weak base and its conjugate salt
- they resist large fluctuations in pH
What is buffering capacity?
the ability of a buffer to resist changes in pH
- maximal buffering capacity is seen within 1 pH point of the pKa of the acid in the buffer solution
What is Henderson-Hasselbalch equation?
quantifies the relationship between pH and pKa for weak acids and between pOH and pKb for weak bases
- when a solution is optimally buffered, pH - pKa and pOH = pKb
pH = pKa + log[A-]/[HA]
pOH = pKb + log[B+]/[BOH]
What is the nomenclature for acids?
- most acids related to parent anion end in -ide
F- fluoride, Cl- chloride, Br- bromide - acids formed from anions have prefix hydro- and end in -ic
HF hydrofluoric acid, HCl hydrochloric acid, HBr hydrobromic acid
What are the common acids from -1 charged polyatomic ions?
ClO- hypochlorite; HClO hypochlorous acid ClO2- chlorite; HClO2 chlorous acid ClO3- chlorate; HClO3 chloric acid ClO4- perchlorate; HClO4 perchloric acid NO2- nitrite; HNO2 nitrous acid NO3- nitrate; HNO3 nitric acid CH3COO- acetate; CH3COOH acetic acid
What are the common acids from -2 charged polyatomic ions?
CO3 2- carbonate; H3CO3 carbonic acid
SO4 2- sulfate; H2SO4 sulfuric acid
CrO4 2- chromate; H2CrO4 chromic acid
What are the common acids from -3 charged polyatomic ions?
PO4 3- phosphate; H3PO4 phosphoric acid
BP3 3- borate; H3BO3 boric acid
How are the acid/base dissociation constants calculated?
HA + H2O H3O+ + A-
Ka = [H3O+][A-]/[HA]
BOH B+ + OH-
Kb = [B+][OH-]/[BOH]
How can the unknown concentration of a titrand be calculated?
NaVa = NbVb
Na and Nb are the acid and base normalities
Va and Vb are the volumes of the acid and base solutions
How can Le Chatelier’s principle be applied to indicators?
indicators change color as they shift between their conjugate acid and base forms:
H - indicator1 H+ + indicator-2
adding H+ shifts the equilibrium to the lect
adding OH= removes H+ and therefore shifts the equilibrium to the right
What is the function of a buffer?
resist change in pH when small amounts of acid or base are added
Where are pKa values found on titration curves?
midpoint between the start and the equivalence points
What is gram equivalent weight?
the weight (in grams) that releases 1 acid or base equivalent from a compounds
How do Ka values relate to pH values?
- a higher Ka implies a stronger acid
- weak acids usually have a Ka that is several orders of magnitude below 1
- the pKa of a compound is the pH at which there are equal concentrations of acid and conjugate base
pKa = -logKa
How is the p scale approximation used?
p value `= M - 0.n
where 0.n is the sliding decimal point of n one position to the left (n/10)
