Acid-Base equilibria Flashcards
What is the pH scale?
A scale used to measure and determine if a solution is acidic, neutral or basic.
It stands for the potential of hydrogen, that is, the concentration of hydrogen ions in a solution
0-6.9 = acidic
7.0 = neutral
7.1 - 14 = basic or alkaline
(lower the acid the stronger it is and vice versa)
Describe the traditional / Arrhenius theory
Acids : its properties were due to the presence of hydrogen atoms
-defined as a compound that produced H+ ions in a aqueous solution
Base : its properties were due to the presence of OH- ions
-defined as a compound that produces OH- ions in aqueous solutions
This theory explained a lot of acid-base chemistry but was limited because it only described one type of base, those containing the OH- ion
Describe the Bronsted-Lowry Theory
Acid : proton donor
Base : proton acceptor
theory : sometimes the the H+ ion is not stable enough on its own so it reacts with water to form the hydronium ion
*look at picture for diagram
What is an Amphiprotic Substance?
A substance that can act as both a Bronsted - Lowry acid or base, depending on the reaction.
What is a conjugate acid / base?
Since acid-base reactions are reversible, a proton transfer may happen in the forward reaction and the reverse reaction.
- When the acid or base are on the product side it’s called the conjugate acid or base
-The pairs only differ by a hydrogen ion (a proton)
Describe the conjugate acid
It’s the substance that forms when a base accepts a proton
Describe the conjugate base
It’s the substance that forms when an acid loses a proton
Describe strong & weak acids and its H+ ions
Strong acids : produce many H+ ions
Weak acids : produce few H+ ions
The stronger the acid the more H+ ions are produced.
Describe strong & weak bases and its OH- ions
Strong base : produce many OH- ions
Weak base : produce few OH- ions
The stronger the base, the more OH- ions are produced
What kind of reactions are strong acid and bases?
They’re essentially one way reactions - the acid or base breaks down completely to produce ions.
What kind of reactions are weak acid and bases?
They do not ionize completely, which is represented by a double arrow.
For weak electrolytes, equilibrium lies to the left side of the equation (reactant).
What are ionization constants?
Since acid/base solutions are systems at equilibrium we can write equilibrium constant expressions for the systems
Acids : Ka
Base : Kb
Water : Kw
What do large Ka and Kb mean?
-A large Ka means there are many H+ ions in a solution, so a strong acid
-A large Kb means there are many OH- ions in a solution, so a strong base
Key points about Kw
The value is given
- As long as temperature remains constant Kw does not change
-The value is very small, meaning that very few ions are present. Most water remains “intact” as H2O, and few ions form
What is an acid-base titration?
A process used to determine the concentration of an acid solution or base solution. An acidic or basic solution of known concentration is used to neutralize a known volume of a basic or acid solution with an unknow concentration.
What is the equivalence point?
Occurs when the number of moles of base is neutralized by equal number of moles of acid.
What is the end point?
The moment at which the reaction signals that the equivalence point has been reached. Often indicated by a sudden colour change of the indicator.
What is an indicator?
A dye that changes colours under varying pH.
-It’s used in an acid-base titration to tell when the acid and base have neutralized each other.
What is a titration curve?
A graph of pH vs volume titrant added. The center of the vertical region of the curve indicated the equivalence point.
Strong Acid & Strong Base
pH of 7
- only combo that results in the solution to be neutral
Strong Acid & Weak Base
pH of 5
Weak Acid & Strong Base
pH of 9
