Exambusters Study Cards 16 Acids and Bases

Ionization Constant
Kw = 1 X 10-14 at 25 °C
pH
pH = -log[H+]
For what pH values is a solution acidic?
< 7
For what pH values is a solution neutral?
= 7
For what pH values is a solution basic?
> 7
pOH
pOH = -log[OH]
For what pOH values is a solution acidic?
> 7
For what pOH values is a solution neutral?
= 7
For what pOH values is a solution basic?
< 7
How are pH and pOH of a solution related?

The sum of the two values = 14

pH + pOH = 14

How are the concentrations of [H+] and [OH] related in a solution?

The product of the concentrations = 1 x 10-14

[H+][OH] = 1 x 10-14

Match pH value to distilled water.

a.) pH=2

b.) pH=7

c.) pH=12

b.) pH = 7

Match pH value to lye.

a.) pH=2

b.) pH=7

c.) pH=12

c.) pH= 12

Match pH value to stomach juice.

a.) pH=2

b.) pH=7

c.) pH=12

a.) pH=2
For a solution with a pH of 3, find pOH
pOH = 11
For a solution with a pH of 3, find [H+]
[H+] = 1 x 10-3
For a solution with a pH of 3, find [OH]
[OH] = 1 x 10-11
Solubility Product Constant – Ksp
An equilibrium exists in a saturated solution between dissolved and undissolved solute. “Ksp” is the equilibrium constant for this reaction.
Write the solubility product expression for AgCl double arrow Ag+ = Cl
Ksp = [Ag+][Cl]

In a saturated solution of BaSO4, [Ba2+] = 2 x 10-5.

Find Ksp.

Each molecule of BaSO4 that ionizes produces equal concentrations of ions; therefore;

[Ba2+] = [SO42-]

Ksp = [Ba2+][SO42-]

Ksp=[2 x 10-5][2 x 10-5]

Ksp = 4 x 10-10

Common Ion Effect
When an ionization reaction is at equilibrium, and additional ion is added, the reverse reaction rate increases to consume the added ion.

NaCl ↔ Na+ = Cl

What happens when Cl is added to this system at equilibrium?

According to the common ion effect, the reverse reaction will speed up, consuming Na+ and Cl, and more NaCl will be formed.
Six common characteristics of ACIDS

form H2O solutions

conduct electricity

react with active metals

turn blue litmus red

neutralize bases

sour taste

Seven common characteristics of BASES

form H2O solutions

conduct electricity

turn red litmus blue

feel slippery

caustic

neutralize acids

bases + fats form soap

Strong Acids

nitric

hydrochloric

sulfuric

hydriodic

hydrobromic

perchloric

Weak Acids

hydrofluoric

acetic

carbonic

and most others

Moderately Strong Acids

oxalic

phosphoric

sulfurous

Strong Bases

hydroxides of:

potassium

sodium

barium s

trontium

calcium

 

also:

KOH

NaOH

Hydronium ion

H3O+ ion found in water solutions of acids.

Water molecule with a proton attached.

Neutralization Reaction
acid + base → salt + water
Write the equation for hydrochloric acid and sodium hydroxide.
HCl + NaOH → NaCl + H2O
Arrhenius Theory
An acid yields protons in solution. (H+ ions) A base yields hydroxide ions in solution. (OH ions)
Bronsted-Lowry Theory

An acid is a proton donor.

A base is a proton acceptor.

Lewis Theory

An acid is an electron pair acceptor.

A base is an electron pair donor.

Conjugate Base: Write conjugate base of HCl.
When a Bronsted acid donates a proton, it becomes its conjugate base. Conjugate base of HCl is Cl.
Conjugate Acid: Write conjugate acid of I
When a Bronsted base accepts a proton, it becomes its conjugate acid. Conjugate acid of I is HI.
Indicator

A substance which changes color along the pH scale.

e.g. litmus, phenolphthalein, methyl orange, bromthymol blue

Titration
A process of finding the unknown concentration of a solution by allowing it to react with another solution of known volume and concentration.
Endpoint
The point during a titration at which the acid reacts completely with the base. The indicator changes color.
Write the equation to calculate concentrations and volumes in titration reactions.

MA X VA = MB x VB

 

molarity = M

volume = V

acid = A

base = B

Calculate the volume of 10 M NaOH needed to titrate 5L of 2M HCl

MA X VA = MB X VB

2M X 5L = 10M X VB

1L = volume of base

Buffer Solutions
Equilibrium systems which resist changes in pH upon the introduction of acids or bases (due to the common ion effect). e.g. a weak acid (acetic acid) and its salt (sodium acetate)
Electrolysis
The passage of a direct electric current through an ionic solution, producing chemical changes at the electrodes.