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