Chemistry Acids and Bases Definitions

Study Notes

Brønsted-Lowry Definition of Acids and Bases

Acids are proton donors.
Bases are proton acceptors.
This definition is more general than the Arrhenius definition, encompassing a wider range of substances.
Examples:
- HCl (hydrochloric acid) donates a proton to form Cl− (chloride ion), acting as an acid.
- NH3 (ammonia) accepts a proton to form NH4+ (ammonium ion), acting as a base.

Arrhenius Definition of Acids and Bases

Acids produce H+ ions in aqueous solutions.
Bases produce OH− ions in aqueous solutions.
This definition is limited to aqueous solutions.
Examples:
- Hydrochloric acid (HCl) dissociates into H+ and Cl− ions in water.
- Sodium hydroxide (NaOH) dissociates into Na+ and OH− ions in water.

Conjugate Acid-Base Pairs

When an acid loses a proton, it forms its conjugate base.
When a base gains a proton, it forms its conjugate acid.
These pairs are related by the transfer of a single proton.
Example:
- HCl (acid) loses a proton to form Cl− (conjugate base)
- H2O (base) gains a proton to form H3O+ (conjugate acid)

Strengths of Acids and Bases

Strong acids and bases completely dissociate in water.
Weak acids and bases partially dissociate in water.
The strength of an acid or base is determined by its tendency to donate or accept protons.
Strong acids: HCl, H2SO4, HNO3
Strong bases: NaOH, KOH, Ca(OH)2
Weak acids: acetic acid (CH3COOH), carbonic acid (H2CO3)
Weak bases: ammonia (NH3), amines

pH Scale

A measure of the concentration of H+ ions in a solution.
Ranges from 0 to 14.
pH 7 is neutral (water).
pH < 7 is acidic.
pH > 7 is basic.
Logarithmic scale (a change of one pH unit corresponds to a tenfold change in H+ concentration).

Neutralization Reactions

A reaction between an acid and a base.
The products are a salt and water.
The H+ ions from the acid react with the OH− ions from the base to form water.
Example:
- HCl + NaOH → NaCl + H2O

Salts

Ionic compounds formed from the reaction of an acid and a base.
Consist of a cation (positive ion) from the base and an anion (negative ion) from the acid.
Can be acidic, basic, or neutral depending on the strength of their constituent ions.
Example:
- NaCl (sodium chloride) is a neutral salt.
- NH4Cl (ammonium chloride) is an acidic salt.
- Na2CO3 (sodium carbonate) is a basic salt.

Acid-Base Titrations

A method used to determine the concentration of an unknown acid or base solution.
A solution of known concentration (standard solution) is added to the unknown solution until the reaction is complete.
The equivalence point is reached when the moles of acid equal the moles of base.
Indicators are used to visually detect the equivalence point.

Indicators

Substances that change color depending on the pH of the solution.
Used to signal the end point of a titration.
Common indicators include phenolphthalein (colorless in acid, pink in base) and methyl orange (red in acid, yellow in base).

Acid Rain

Acidic deposition from the atmosphere.
Formed when sulfur dioxide (SO2) and nitrogen oxides (NOx) react with water, oxygen, and other chemicals to form various acidic compounds.
Causes damage to ecosystems, including water bodies, forests, and structures.

Buffers

Solutions that resist changes in pH.
Consist of a weak acid and its conjugate base, or a weak base and its conjugate acid.
Maintain a relatively constant pH when small amounts of acid or base are added.
Important in biological systems to maintain homeostasis.

Description

Explore the Brønsted-Lowry and Arrhenius definitions of acids and bases in this quiz. Understand the concept of conjugate acid-base pairs and their importance in chemical reactions. Test your knowledge with examples and definitions that illustrate these foundational ideas.