AP Chemistry Unit 8 - Acid Base Equilibrium

Acid

Any compound that contains H+ ions

Acid Properties

sour taste, red litmus paper result, electrolytes

Base

Any compound that contains OH- ions

Base Properties

bitter taste, slippery feel, blue litmus paper result

pH scale

scale with values from 0 to 14, used to measure the concentration of H+ ions in a solution

What does p stand for?

- log

Describe H+ and OH- for an acidic solution?

[H+] > [OH-] / pH 0-6

Describe H+ and OH- for a basic solution?

[H+] < [OH-] / pH 8-14

Describe H+ and OH- for a neutral solution?

[H+] = [OH-] / pH 7 (Water)

Bronsted-Lowry acid

proton donor

Bronsted-Lowry base

proton acceptor

Conjugate base

the particle that remains when an acid has donated a hydrogen ion (lost the H+)

Conjugate acid

the particle formed when a base gains a hydrogen ion (gained the H+)

Hydronium Ion

hydrogen ion combines with a water molecule to form a hydronium ion, H3O(+)

Strong Acids are

HCl, HBr, HI, HNO3, H2SO4, HClO4, HClO3

Strong Acids in water

ionize completely (100% break up in water)

Strong acids have a Ka value...

greater than 1

Strong bases are

Column 1A & 2A + OH

Strong Bases in water

ionize completely (100% break up in water)

Weak Acid

an acid that is only slightly ionized in aqueous solution (any acid not memorized as strong). Will have a small Ka

Weak Base

A base that does not dissociate completely into ions in solution (any base not memorized as strong). Will have a small Kb

Monoprotic Acid

an acid that can donate only one proton (hydrogen ion) per molecule

Diprotic Acid

an acid that can donate two protons per molecule

Triprotic acid

an acid able to donate three protons per molecule

When removing protons from a polyprotic acid, which H+ are the easiest to remove?

the first protons are easier to remove than later ones

Oxyacid

an acid that is a compound of hydrogen, oxygen, and a third element, usually a nonmetal

Amphoteric substances

Substances that can react as both acids and bases

Ka

The equilibrium constant for an acid dissociation in water. The larger the Ka, the stronger the acid

Kb

The equilibrium constant for a base dissolving in water. The larger the Kb, the stronger the base.

Kw

The equilibrium constant for the dissociation of water (1 x 10-14 at room temperature)

Relationship between Ka and Kb

Kw = Ka * Kb

pH scale application

a figure expressing the acidity or alkalinity of a solution on a logarithmic scale on which 7 is neutral, lower values are more acid and higher values more alkaline. The pH is equal to −log [H+]

pH + pOH =

14

how to find pH when given [H3O+]

pH=-log[H3O+]

how to find pOH when given [OH-]

pOH=-log[OH-]

how to find pOH when given the pH

14-pH

how to find the pH when given the pOH

14-pOH

how to find the Ka when given pKa

10^-pKa

how to find the Kb when given the pKb

10^-pKb

how to find the [H3O+] when given pH

10^-pH

how to find the [OH-] when given pOH

10^-pOH

Ka and Kb relationship with Kw

Kw=Ka x Kb

ways to measure pH

litmus paper, electronic digital meter, color indicators in solution

Polyprotic acid equilibrium constants

Each dissociation of a polyprotic acid has a different Ka value. Ka1 for the first dissociation is typically greater than Ka2

Salt

any ionic compound that can be made from the neutralization of an acid with a base

Acidic salt

a salt produced from a strong acid and a weak base

Basic salt

The salt produced from a weak acid and a strong base

Neutral salt

the salt produced from a strong acid and a strong base

Acid strength of oxyacids (number of oxygens)

An oxyacid with more oxygen atoms is stronger than one with fewer (e.g. HClO is weaker than HClO3)

what does and acid-base equilibrium favor

weak acid and weak base

hydrolysis

states that salts (ionic compounds) can make a solution acidic, basic, or even have no effect on the pH

As the temperature of water increases the pH

of water decreases

As the temperature of water decreases the pH

of water increases

Do we write the Ka expression for strong acids bases?

No! They dissolve completely

Do we write ICE charts for strong acids or bases?

No! They dissolve completely

When finding the K values of polyprotic acids, what do me find?

ONLY find Ka1

Why is it unimportant to find the other Ka values (2,3,4)?

They are so much smaller than the original that they have little effect on the overall value?

What is the equation for the percent dissociation of weak acids?

(H+ at equilibrium/acid initial) x100

What is the equation for the percent dissociation of weak bases?

(OH- at equilibrium/base initial) x100

What is the common ion effect?

if you have a system at equilibrium and add a solute that contains one of the ions in equilibrium then the equilibrium will shift