Join Our Discord

Learn Moreย ย ๐Ÿ‘‡

caret down
caret up

Join our Discord

1,000s of Fiveable Community students are already finding study help, meeting new friends, and sharing tons of opportunities among other students around the world! Don't miss out!ย  ๐ŸŽ‰

group of students
group of students

๐Ÿงชย ap chem

ย ย >ย ย 

๐ŸŠย Unit 8

ย ย โ€ขย ย โฑ๏ธ2 min read

8.1 Introduction to Acids and Bases

Jacob Jeffries

jacob jeffries

Dylan Black

dylan black


โฑ๏ธ June 10, 2020


Types of Acids and Bases

Arrhenius Definition

There are two main schools of thought for what should be the definitions for acids and bases. The Arrhenius definition of an acid is any compound that increases the concentration of hydrogen ions ([H+]) in a solution, while the Arrhenius definition of a base is any compound that increases the concentration of hydroxide ions ([OH-]) in solution. Essentially, the Arrhenius definition of an acid/base is anything that yields H+ or OH- respectively in water. For example, HCl (hydrochloric acid) can be described as an Arrhenius acid because in water the following reaction occurs:

HCl โ†’ H+ + Cl-

Thus, HCl yields an H+ ion in water, making it an Arrhenius acid.

Brรธnsted-Lowry Definition

Meanwhile, the Brรธnsted-Lowry definition of acids and bases define acids and bases in the form of a donation reaction. Basically, an acid/base is seen rather as an H+ donator or accepter (the acid donates, the base accepts):

HA + B- โ†’ HB + A-

In this example, HA is the acid, which donates an H+ ion to the B- ion (the base) to form HB and A-. Quick tip, get used to seeing HA and B- as sample acids and bases, it's just notation. A and B could be standins for any number of ions that fit in. Quick thinkers may be wondering about the reverse reaction in the case that HA + B- is an equilibrium reaction:

HA + B- โ‡„ HB + A-

The Hydronium Ion

A consequence of Bronsted Acids and Bases is that when an acid dissolves in water, it needs something to donate it's H+ to! In this case, it donates it to water, creating H3O+, or hydronium. Thus, we can see the dissolution of an acid both in an Arrhenius sense as HA <--> H+ + A- and a Bronsted sense as HA + H2O <--> H3O+ + A-. Both of these essentially mean the same thing (and when we learn pH, we'll find that [H+] = [H3O+]), but they display the difference between Arrhenius and Bronsted Acids.

Conjugate Acids and Bases

How do we classify HB and A- then? Wouldnโ€™t A- be a base and HB be an acid if the reaction were reversed? The answer is short: yes. However, they are given a special name: HB is called the conjugate acid of B-, and A- is called the conjugate base of HA. In the case that HA is a weak acid and B- is a weak base, HB and A- would be considered to have significant acidity/basicity. The conjugate acid/base of a strong base/acid does not have acidity/basicity. The weaker the acid/base, the stronger the conjugate base/acid.

A tent in the woods with a fire

Get your ap chem survival pack!

Download our ap chem survival pack and get access to every resource you need to get a 5.

ap chem study guides

โš›๏ธย  Unit 1: Atomic Structure and Properties

๐ŸŒ€ย  Unit 3: Intermolecular Forces and Properties

๐Ÿงชย  Unit 4: Chemical Reactions

๐Ÿ‘Ÿย  Unit 5: Kinetics

๐Ÿ”ฅย  Unit 6: Thermodynamics

โš–๏ธย  Unit 7: Equilibrium

ย  Unit 9: Applications of Thermodynamics

๐Ÿคบย  AP Chemistry Essentials

continue learning

Slide 1 of 4

Join Our Discord


Fiveable Community students are already meeting new friends, starting study groups, and sharing tons of opportunities for other high schoolers. Soon the Fiveable Community will be on a totally new platform where you can share, save, and organize your learning links and lead study groups among other students!๐ŸŽ‰

*apยฎ and advanced placementยฎ are registered trademarks of the college board, which was not involved in the production of, and does not endorse, this product.

ยฉ fiveable 2021 | all rights reserved.

2550 north lake drive
suite 2
milwaukee, wi 53211