Chapter 16 Learning Objectives
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Objectives for chapter 16 on Acid-Base Equilibria
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40 Terms
A substance that has H in their formulas and dissociate in water to donate H+
What is an Arrhenius acid?
A substance that has OH- in their formulas and they dissociate in water to donate OH-
What is an Arrhenius base?
HCl → H3O+ + Cl-
Identifying Arrhenius acids in chemical formulas.
NaOH → Na+ + OH-
Identifying Arrhenius bases in chemical formulas.
H3O+
Produced when H+ ions react with water molecule. H+ ions produced by acid are so reactive they cannot exist in water. Hydrogen ions are denoted with aqueous (aq), which is equivalent to saying hydronium ions
What is the hydronium ion?
A hydrogen ion (H+) reacts with a water molecule (H2O)
How is a hydronium ion formed?
Because in water, H+ immediately bonds with a water molecule to form and H3O+; they are highly reactive.
Why do scientists often use the terms for hydrogen and hydronium ions interchangeably?
A neutralization reaction that forms water and salt.
acid + base → salt + H2O
What happens in a reaction between an Arrhenius acid and Arrhenius base?
A proton donor
What is a Bronsted-Lowry acid?
A proton accepter
What is a Bronsted-Lowry base?
Add one hydrogen and add one to the charge
How do you find the conjugate acid of a Bronsted-Lowry acid?
Remove one hydrogen and subtract one from the charge
How do you find the conjugate acid of a Bronsted-Lowry base?
A strong acid/base completely ionizes in solution, while a weak acid/base only partially ionizes.
What is the difference between a strong acid/base and a weak acid/base?
A strong acid/base is 100% ionized in solution.
How much of a strong acid/base is ionized?
A weak acid/base is partially ionized, typically less than 5-10% depending on concentration and equilibrium constants.
How much of a weak acid/base is ionized?
H3O+ is equal to the initial concentration of the acid because it completely ionizes in solution.
How does the concentration of hydronium ion [H3O+] relate to the initial concentration of acid for a strong acid?
H3O+ is less than the initial concentration of the acid because only a fraction of the acid ionizes in solution.
How does the concentration of hydronium ion H3O+ relate to the initial concentration of acid for a weak acid?
HCl, HBr, HI, HClO3, HClO4, HNO3, H2SO4
What are the strong acids?
NaOH, KOH, LiOH, RbOH, Ca(OH)2, Ba(OH)2, Sr(OH)2
What are the strong bases?
The acid ionization constant (Ka) is a measure of the strength of an acid in solution. It represents the equilibrium constant for the dissociation of an acid into its conjugate base and hydrogen ions.
What is the acid ionization constant?It quantifies the extent to which an acid donates protons in a solution, with a higher Ka indicating a stronger acid.
The symbol for the acid ionization constant is Ka.
What is the symbol for the acid ionization constant?
A higher Ka value indicates a stronger acid because it means the acid dissociates more in solution, releasing more hydrogen ions. A lower Ka value indicates a weaker acid, as it dissociates less.
How is Ka related to the strength of an acid?
The acid with a high Ka is stronger because it dissociates more completely in solution, producing more hydrogen ions.
Which is a stronger acid: one with a low Ka or one with a high Ka?
Write the general acid equation: HA (aq) ⇌ H+(aq) + A- (aq)
Use the equilibrium expression: K_{a}=\dfrac{\left[ A^{-}\right] \left[ H^{+}\right] }{\left[ HA\right] }
How do you write an equilibrium expression for the dissociation of any acid?
An acid-base reaction will proceed in the direction that forms the weaker acid and weaker base (equilibrium favors the side with the lowest energy)
How can you predict the direction of an acid-base reaction using relative strengths of acids and bases?
It is the process where water molecules spontaneously dissociate into hydronium (H3O+) and hydroxide (OH-) ions
What is the auto-ionization of water?
What is the equilibrium expression for the auto-ionization of water and it’s value at 25°C?
K_{W}=\left[ OH^{-}\right] \left[ H_{3}O^{+}\right]
At 25°C, Kw = 1.0×10-14
Neutral solutions have equal amounts of [H3O+] and [OH-].
What is the relationship between hydronium ion [H3O+] and hydroxide ion [OH-] concentrations in a neutral solution?
Acidic solutions have a greater amount of [H3O+] than [OH-].
What is the relationship between hydronium ion [H3O+] and hydroxide ion [OH-] concentrations in an acidic solution?
Basic solutions have a greater amount of [OH-] than [H3O+].
What is the relationship between hydronium ion [H3O+] and hydroxide ion [OH-] concentrations in a basic solution?
It is a logarithmic scale used to measure the acidity or basicity of a solution.
What is a “p” scale?
“potential of”
What does “p” mean?
A change of one pH unit corresponds to a tenfold (10x) change in the concentration of (H+) because the pH is logarithimic.
If the pH changes by 1 unit, what is the corresponding change in concentration?
Use the equation pH = -log[H3O+]
How do you solve for pH when given the hydronium ion concentration?
pH = 7
What is the pH for a neutral solution at 25°C?
pH < 7
What is the pH for an acidic solution at 25°C?
pH > 7
What is the pH for a basic solution at 25°C?
pOH = -log[OH-]
pKa = -logKa
14 = pH + pOH
What equations can be used when solving for pOH, pKa, [OH-], and Ka?
Inversely related (when one increases, the other decreases and vice versa)
Example: lower pKa value = stronger acid
How is pKa related to acid strength?
If Ka value is greater than 400 then we can assume x is small therefore would not make a difference and can be ignored. This avoids using the quadratic formula.
How can you simplify equilibrium calculations? Under which conditions is this simplification valid?