Chemistry 102: Chapter 16

What is acid ionization equilibria?

Acid ionization equilibria refers to the balance established when an acid donates protons ($H^+$ ions) to water, resulting in the formation of hydronium ions

what is ka formula mean?

The $K_a$ formula represents the acid dissociation constant, which quantifies the strength of an acid in solution by measuring the extent to which it ionizes to produce hydronium ions. It is defined as the ratio of the concentration of products to reactants at equilibrium.

true or false

weak acids fully ionize

False, weak acids do not fully ionize in solution.

true or false

strong acids fully ionize in water

True, strong acids fully ionize in water, releasing all of their protons into the solution.

How do we determine the concentration of weak acids?

We determine the concentration of weak acids by using the acid dissociation constant ($K_a$) and the equilibrium expression, allowing us to calculate the concentration of hydronium ions and the weak acid present at equilibrium.

what is the generic acid chemical reaction to find the acid dissociation constant (Ka) ?

HA(aq) + H2O(l) m H3O+(aq) + A−(aq)

what is the formula for the equilibrium constant Ka or acid-ionization constant?

why is the degree of ionization also called % ionization ?

The degree of ionization is the fraction of a weak acid that has dissociated into ions in solution, often expressed as a percentage of the initial concentration.

what is the degree of ionization formula?

fill in the blank

the ___ the Ka the greater the degree of ionization

larger

Read

Equilbria involving weak bases are treated similarly to those of weak acids

what is the kb formula?

The base dissociation constant, $K_b$, is a measure of the extent to which a base ionizes in solution, defined as the ratio of the concentration of products to the concentration of reactants at equilibrium.

what is the generic formula for a base?

B(aq) + H2O(l) m HB+(aq) + OH−(aq) where B is the base.

What is the Kb expression?

true of false

the common-ion effect can be done to both acidic and basic solutions

True. The common-ion effect occurs when a salt containing an ion common to the dissolved species is added to a solution, affecting the equilibrium of both acidic and basic solutions.

what is a buffer?

A buffer is a solution that resists changes in pH when small amounts of acid or base are added. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid.

Is a conjugate base always an anion?

Yes, a conjugate base is always an anion formed when an acid donates a proton.

What are salt made of?

ionic compound positive cation and negative anion, formed from the reaction of an acid and a base.

Solve the practice problem in slide 19

Sore-throat medications sometimes contain the weak acid phenol, HC₆H₅O. A 0.10 M solution of phenol has a pH of 5.43 at 25°C.

  a.  What is the acid-ionization
  constant, K_a, for phenol at 25°C?

  b.  What is the degree of ionization?

refer to slide 20-22 for answer and steps

Read

Simplifying Assumption for Acid and Base Ionizations

The equilibrium concentration of the acid is most often ([HA]₀ – x).

If x is much, much less than [HA]₀, we can assume that subtracting x makes no difference to [HA]:

([HA]₀ – x) = [HA]₀

This is a valid assumption when the ratio of [HA]₀ to K_a is > 10². If it is not valid, you must use the quadratic equation to solve the problem.

Solve the practice problem in slide 24

Para-hydroxybenzoic acid is used to make certain dyes. What are the concentrations of this acid, of hydronium ion, and of para-hydroxybenzoate ion in a 0.200 M aqueous solution at 25°C? What is the pH of the solution and the degree of ionization of the acid? The K_a of this acid is 2.6 × 10^-5.

We will use the generic formula HA for para-hydroxybenzoic acid and the following equilibrium:

HA + H₂O   ⇌   H₃O⁺ + A^-

refer to slide 25-26 for answer and steps

Solve the practice problem in slide 41

Aniline, C₆H₅NH, is used in the manufacture of some perfumes. What is the pH of a   0.035 M solution of aniline at 25°C?

K_b= 4.2 × 10^-10 at 25°C.

refer to slide 25-26 for answer and steps

What is hydrolysis?

Hydrolysis is a chemical reaction in which water reacts with a substance, typically resulting in the breakdown of that substance into two or more components. This process often occurs with salts, acids, or bases in solution, impacting their behavior in aqueous environments.

in chemistry it is the conjugate acids and the (OH-) ion

or the conjugate base with the (H3O+) ion

Fill in the blank

F- is the Conjugate ____ of HF, a ____ acid, it is ____

base, a weak acid, basic

How does NaClO dissociate? is it a acidic, basic, or neutral? if it is acidic or basic is it strong or weak?

NaClO dissociates in water to form Na⁺ and ClO^- ions, contributing to its properties as a bleaching agent and disinfectant. It is basic and weak.

read

conjugate acids of strong bases or weak acids, often involved in acid-base equilibrium calculations. Therefore there is no reaction

Realization

weak conjugate acids and bases of strong acid/ bases do not react w/ water!!!

read

The conjugate acid of a weak base reacts with water to form an acidic solution:

NH₄⁺ + H₂O <==> NH₃ + H₃O⁺

read

The conjugate base of a weak acid reacts with water to form a basic solution:

F^- + H₂O <==> HF + OH^-

Fill the in the blank

The hydrolysis equilibrium ___ can be used in problems to determine the pH of a salt solution. To use it we must compute the __ value for it.

constant'; K

Slide #57

What is K_b for the F^- ion, the ion added to the public water supply to protect teeth?

For HF, K_a = 6.8 × 10^-4.

Slide #57

Slide #63

what is the common-ion effect?

The common-ion effect is the shift in an ionic equilibrium caused by the addition of a solute that takes part in the equilibrium

Slide #64

Calculate the pH of a 0.10 M HF solution to which sufficient sodium fluoride has been added to make the concentration 0.20 M NaF. K_a for HF is 6.8 × 10^-4.

We will use the acid equilibrium for HF.

NaF provides the conjugate base, F^-, so             [F^-] = 0.20 M

use slides 65-66 for help

Slide #67

what are buffers?

A buffer is a solution that resists changes in pH when small amounts of acid or base are added. It typically consists of a weak acid and its conjugate base or a weak base and its conjugate acid.

Slide #70

What is the pH of a buffer made by mixing 1.00 L of 0.020 M benzoic acid, HC₇H₅O₂, with 3.00 L of 0.060 M sodium benzoate, NaC₇H₅O₂? K_a for benzoic acid is 6.3 × 10^-5.

use slides 71-73 for help

Slide #74

what is the henderson-hasselbach equation used for?

The Henderson-Hasselbalch equation is used to calculate the pH of buffered solutions. It relates the pH to the pKa of the weak acid and the ratio of the concentrations of its conjugate base to the weak acid.

Slide #74

what is henderson-hasselbach formula?

Slide #75

Flip the formula for another way to see the formula

pKa=-log (Ka)

Slide #76

solve the problem on slide #75

use slide #76 as a guide

Slide #78

what is acid-base titration?

A laboratory technique used to determine the concentration of an acid or base by neutralizing it with a base or acid of known concentration. Indicators are often used to signal the endpoint of the reaction.

Slide #78

what is an acid-base titration curve?

is a plot of the pH of a solution of acid (or base) against the volume of added base (or acid).

Slide #80

define equivalence point in acid-base titration?

The equivalence point in an acid-base titration is the stage at which the amount of titrant added is chemically equivalent to the amount of the substance being titrated, resulting in complete neutralization.

Slide #80

what happens to the indicator near the equivalence point?

The indicator changes color near the equivalence point, signaling that the pH of the solution is approaching neutrality.

Slide #82

Calculate the pOH and the pH of a solution in which 10.0 mL of 0.100 M HCl is added to 25.0 mL of 0.100 M NaOH.

use slides 83-84 for help