4.8 Introduction to Acid and Bases

​Introduction to Acid and Bases

Multiple Choice

conductivity is a property of ________

• acid

• base

• both

• neither

Multiple Choice

Sour taste is a property of _________

• acids

• bases

• neither

• both

Multiple Choice

Turns red litmus blue is a property of __________

• acid

• base

• both

• neither

​Acids are substances that have the potential to donate a proton. Substances with a pH less than 7 are considered acidic. Bases are substances that can accept protons. Substances with a pH greater than 7 are considered basic.

​Strong vs. Weak
Strong and weak describe the extent that a substance will dissociate (ionize) in a solution.

Strong means that the substance will completely separate into its ions. (disassociate)

Example: Hydrochloric acid (HCl) is a strong acid so the reaction with water is shown below with a single Arrow ( → )to indicate that at the end of the reaction no HCl remains and 100% of it has become H₃O+ + Cl-

​HCl → H+ + Cl- (H₂O catalyst)

HCl + H₂O → H₃O+ + Cl-

​Strong vs Weak

Weak means that the substance will only partially separate into its ions.

The most common weak acid we use is acetic acid, vinegar, HCH₃COO. The most common weak base we use is ammonia, NH₃. (ammonia)

Example: A weak acid such as acetic acid, HC₂H₃O₂ is shown below with a double arrow (⇌) to indicate that at the end of the reaction some of the acetic acid will remain because less than 100% of it has become H₃O+ and C₂H₃O₂^_

​HC₂H₃O₂ + H₂O ⇌ H₃O+ + C₂H₃O₂^_

​Strong vs. Weak


Strong Acids to memorize: HI, HClO_4, HCl, HBr, H₂SO_4, HNO₃

“ Imagine A Perfectly Clear Breezy Summer Night”

Strong Bases to memorize: LiOH, NaOH, KOH, RbOH, Ca(OH)_2, Sr(OH)_2, Ba(OH)₂
All the cations are located in Group 1 and 2.

Multiple Choice

pH > 7 is a property of

• acid

• base

• both

• neither

Multiple Choice

Completely ionizes in water is a property of a ________

• weak acid

• weak base

• strong acid

• strong base

Multiple Choice

Hydrochloric acid is a __________

• weak acid

• weak base

• strong acid

• strong base

Multiple Choice

Partially ionizes in water is a property of a _______

• weak acid

• weak base

• strong acid

• strong base

Multiple Choice

Sodium hydroxide is a _______________

• weak acid

• weak base

• strong acid

• strong base

Multiple Choice

Hydrofluoric acid is a __________

• weak acid

• weak base

• strong acid

• strong base

​Dilute vs. Concentrated

Dilute and concentrated are ways to describe the amount of a substance in a solution.

Dilute describes a solution with a small amount of solute dissolved and has a low molarity.

Concentrated describes a solution with a large amount of solute dissolved and has a high molarity.

​M₁V₁ = M₂V₂

​Typically, and pure water at 25°C, the concentration of both the ions equals 1.0 x10 -7  mol/L so water is neutral and pH = 7.

Multiple Choice

The part of a solution that does the dissolving is called the ______

• solution

• molarity

• solvent

• solute

Multiple Choice

The part of a solution that is dissolved is the __________

• solution

• molarity

• solvent

• solute

Multiple Choice

The amount of solute in moles per solvent in liters is called __________

• solution

• molarity

• solvent

• solute

​Acid-Base Reactions

In an acid-base reaction a hydrogen ion is transferred from the acid to the base.

When an acid loses a hydrogen ion, it becomes the conjugate base. The acid and the conjugate base make a conjugate acid-base pair.

When a base gains a hydrogen ion it becomes the conjugate acid. The base and the conjugate acid also become an acid-base pair.

The conjugate acid-base pair will always differ by only one proton. The conjugate acid has the ability to donate a hydrogen ion in the reverse (flipped) reaction, while the conjugate base could accept the hydrogen in the reverse reaction.

Water is a unique species in that it can act as either an acid ( by donating a proton and becoming hydroxide, OH-) or a base ( by accepting a proton and becoming hydronium H3O⁺)​



Substances that can act as both a base and an acid, are often described as being amphoteric. The amphoteric nature of water explains why there are small amounts H+(aq) and OH^1-(aq) of present in what should be a covalent substance

​H₂O(l) + H₂O(l) ⇌ H₃O+(aq) + OH^1-(aq)

​It is also important to know that:
a stronger acid will form a weaker conjugate base,
a weaker acid will form a stronger conjugate base,
a stronger base will form a weaker conjugate acid,
and a weaker base will form a stronger conjugate acid

An acid-base reaction will favor the formation of the weaker acid and base. The conjugate of a strong acid or a strong base has no acidic or basic properties.

​If the acid is strong and the conjugated base that is formed is a very weak bases then the reaction will not be reversible →

The example below Cl^_ ion is a very weak base and will struggle to accept a proton to reform HCl molecule




  HCl(aq)      +        H₂O(l)       →  H₃O+(aq)  + Cl- (aq)
Acid Base
(proton donor) (proton acceptor)

​If the base that is a weak base then the reaction will be reversible ⇌.
This time, because NH3 is a weak base the NH4+ will be able to donate a proton and reform ammonia molecule.


NH₃(aq)       +           H₂O(l) ⇌    NH₄+(aq)   +  OH^1-(aq)

Base                      Acid
(proton acceptor) (Proton donor)

Multiple Choice

In the following acid-base reaction CH₃CO₂H(aq) is a

CH₃CO₂H(aq) + H₂O(l) ⇋ CH₃CO₂⁻(aq) + H₃O⁺(aq)

• weak acid

• weak base

• strong acid

• strong base

Multiple Choice

In the following acid-base reaction CH₃CO₂H(aq) will _______

CH₃CO₂H(aq) + H₂O(l) ⇋ CH₃CO₂⁻(aq) + H₃O⁺(aq)

• completely dissociate

• partially dissociate

• neutralize

• no reaction

Multiple Choice

In the following acid-base reaction CH₃CO₂^- (aq) is the

CH₃CO₂H(aq) + H₂O(l) ⇋ CH₃CO₂⁻(aq) + H₃O⁺(aq)

• conjugate acid

• conjugate base

• neutralized acid

• neutralized base

Multiple Choice

H₃O⁺

• hydrogenated ion

• hydroxide ion

• hydronium ion

• trihydrogen oxide

Multiple Choice

#1

• A

• B

• C

• D

Multiple Select

#2

NO^2-(aq) +  H₂O(l)  ⇔ HNO₂(aq) + OH^-(aq)

• acid: H₂O

  Conjugate base: OH^-

• acid: HNO₂

  Conjugate base: NO^2-

• acid: HNO₂

  conjugated base: H₂O

Multiple Choice

#3 strong acid

• nitrous acid

• oxalic acid

• not enough information to determine which is stronger