Acid-Base Test
In titrating 0.20 M hydrochloric acid, HCl, with 0.20 M NaOH at 25°C, the solution at the equivalence point is
0.10 M NaCl
Which of the following solutions has a pH greater than 7.0?
0.10 M NaF
Consider the following indicators and their pH ranges: Methyl orange 3.2-4.4 Methyl red 4.8-6.0 Bromothymol blue 6.0-7.6 Phenolphthalein 8.2-10.0 Alizarin yellow 10.1-12.0 Assume an indicator works best when the equivalence point of a titration comes in the middle of the indicator range. For which of the following titrations would methyl red be the best indicator?
0.100 M NH3 (Kb = 1.8 10-5) + 0.100 M HCl
Commercial vinegar was titrated with NaOH solution to determine the content of acetic acid, HC2H3O2. For 20.0 milliliters of the vinegar, 32.0 milliliters of 0.500-molar NaOH solution was required. What was the concentration of acetic acid in the vinegar if no other acid was present?
0.800 M
Kw = [H+][OH-] =
1.0x10-14
[H+] = [OH-] =
10^-pH 10^-pOH
The pH of 0.1-molar sodium hydroxide is
13
pKw = pH + pOH =
14.00
Which of the following would be the best mole ratio of conjugate acid to conjugate base for a large buffer capacity?
1:1
Amphiprotic
A molecule (or compound) that can both donate and accept a proton (both an acid and a base)
[H+] > [OH-]
Acidic solution
Bronsted-Lowry
An acid is a proton donor A base is a proton acceptor
The common ion affect
An aspect of Le Chateiler's principle reduction of extent of ionization and dissociation of a compound when another ionizable and dissociable compound with a common ion is added to the solution
Reactions of anions with water
Anions react with water in hydrolysis
H2O(l) + H2O(l) >< H3O(aq) + OH-(aq) is to referred to as...
Auto-ionization
Weak bases
Bases react with water to produce OH-
[H+] < [OH-]
Basic solution
What is the pH of a 1.0´ 10-2 M solution of HCN? (For HCN, Ka = 4.0 ´ 10-10.)
Between 4 and 7
Reactions of cations with water
Cations with acidic protons will lower the pH of a solution
Which of the following reactions does NOT proceed significantly to the right in aqueous solutions?
H2O + HSO4- -> H2SO4 + OH-
The equilibrium constant for the reaction represented by the equation above is greater than 1.0. Which of the following gives the correct relative strengths of the acids and bases in the reaction? H2PO4- + HBO3 2- -> HPO4 2- + H2BO3
H2PO4- > H2BO3- and HBO3 2- > HPO4 2-
Rank acetic acid (HC2H3O2), hydrocyanic acid (HOCN), and hydrofluoric acid (HF) in order of increasing strength. Acid Ka HC2H3O2 1.8 x 10-5 HOCN 3.5 x 10-4 HF 6.8 x 10-4
HC2H3O2 < HOCN < HF
You have 100.0 mL of 0.100 M aqueous solutions of each of the following acids: HCN, HF, HCl, and HC2H3O2. You titrate each with 0.100 M NaOH (aq). Rank the pHs of each of the solutions when each are titrated to the equivalence point, from highest to lowest pH. Ka for HCN = 6.2 x 10-10 Ka for HF = 7.2 x 10-4 Ka for HC2H3O2 = 1.8 x 10-5
HCN, HC2H3O2, HF, HCl
Strong Acids
HCl HBr HI HNO3 H2SO4 HClO3 HClO4
Polyprotic acids
Have more than 1 acidic proton. Each dissociation has a different Ka
Oxyacids
In oxyacids in which an OH bonded to another atom Y, the more EN Y is the more acidic the acid
For the equilibrium that exists in an aqueous solution of nitrous acid (HNO2, a weak acid), the equilibrium-constant expression is
K = [H+][NO2-] ------------ [HNO2]
Which of the following salts is most likely to form an aqueous solution having the pH shown in the figure above?
KCl
Ka x Kb =
Kw
Buffers
Measures the ability to resist pH change considers the amount of acid or base the buffer can neutralize before pH changes appreciably
All of the following species can function as Brönsted-Lowery bases in solution EXCEPT
NH4+
You have 100.0 mL of a solution of hydrochloric acid that has a pH of 3.00. You add 100.0 mL of water to this solution. What is the resulting pH of the solution?
None of the above is correct, but the pH must be greater than 3.00.
Factors that affect acid strength
Nonmetal hydrides Oxyacids
Strongest base in water is
OH-
Strong Bases
Soluble hydroxides: -Alkali group (group 1) -Heavier alkaline earth metal hydroxides (Ca2+, Sr2+, Ba2+) -Substances that react with water to from OH-
The greater the Ka the weaker/stronger the acid/base? (pick one)
Stronger. Acid.
As water is heated, its pH decreases. This means that:
The dissociation of water is an endothermic process.
Nonmetal hydrides
The more polar the H-X bond and/or weaker the H-X bond the more acidic the compound
Titration
Used to determined the [ ] of a solute in a solvent by combining a reagent sample of known [ ] to the equivalence point
Arrhenius Acid
When dissolved in water is increases the [H+]
Arrhenius Base
When dissolved in water, increases [OH-]
Reaction between acid and bases...
Yields the conjugate acid and conjugate base
Ka =
[H+] [A-] ---------- [HA]
Percent ionization (dissociation) =
[H3O+] -------- x 100 [HA]
Kb =
[HB] [OH-] ---------- [B-]
If 25.0 mL of 0.451 M NaOH solution is titrated with 0.253 M H2SO4, the flask at the endpoint will contain (besides the indicator phenolphthalein) as the principal components:
dissolved sodium sulfate and water
-log([H+]) =
pH
pH range of a buffer (equation)
pH = pKa + log [A-] [HA]
-log([OH-]) =
pOH
Consider the Ka values for the following acids: Cyanic acid, HOCN, 3.5 x 10-4 Formic acid, HCHO2, 1.7 x 10-4 Lactic acid, HC3H5O3, 1.3 x 10-4 Propionic acid, HC3H5O2, 1.3 x 10-5 Benzoic acid, HC7H5O2, 6.3 x 10-5 Which has the strongest conjugate base?
propionic acid
In any acid-base reaction, the equilibrium will favor the...
reaction that moves the proton to the stronger base
2 NH3 NH4+ + NH2- In liquid ammonia, the reaction represented above occurs. In the reaction NH4+ acts as
the conjugate acid of NH3
In deciding which of two acids is the stronger, one must know:
the equilibrium constant of each acid