Acids and Bases Flashcards
Review: Acids & Bases
What is an acid?
Any compound with a formula that starts with H (other than H2O)
There are two types: oxyacids and binary acids
They are molecular compounds, but behave like ionic compounds when in aqueous solution
What is a base?
Any compound that contains the OH- anion
They are ionic compounds
Arrhenius Theory of Acids & Bases
These definitions we’ve been using are what’s called the Arrhenius Theory of acids and bases
Arrhenius Theory
An ACID is a molecular compound that ionizes to produce hydrogen ions in water
A BASE is an ionic compound that dissociates to produce hydroxide ions in water
Ionization vs. dissociation
Ionization: The formation of new ions from an uncharged molecule
Dissociation: The separation of ions that already exist in a neutral compound
BOTH dissociation and ionization result in the presence of ions in solution!
The strength of an acid
According to Arrhenius, the strength of an acid depends on the extent to which it ionizes
Weak acids partially ionize in water
Note: weak is not the same as dilute. A weak acid can be dilute or concentrated!
Strong & Weak Acids
Strong acids completely ionize:
Other examples: HNO3(aq), HClO4(aq), H2SO4 (aq)
Weak acids partially ionize:
Other examples: H3PO4(aq), H2CO3(aq), HCO2H(aq)
The pH scale
The pH of a solution gives you an indication of the concentration of hydrogen ions in the solution
Important note: one pH unit represents a tenfold change in the acidity or basicity of a solution!
For example, a solution with a pH of 4 is 1000 times more acidic than a solution with a pH of 7
Why? Because 1.0x10-4 is 1000 times larger than 1.0x10-7!
The Arrhenius Theory has limitations…
Some substances have basic properties and yet do not contain hydroxide in their chemical formula!
For example, ammonia (NH3) can produce a pH above 7 when in water, but does not contain OH-
In other words, it is somehow increasing the OH- concentration in the water without doing:
H+(aq) + OH-(aq) 🡪 H2O(l)
