5B4 Acid-Base Equilibrium Flashcards
Analyze the properties and equilibria of strong and weak acids and bases, buffers, and polyprotic acids.
Define:
autoionization
Self-ionization, where water molecules react with each other to form ions.
Autoionization of water results in hydronium (H₃O⁺) and hydroxide (OH⁻) ions in a 1:1 molar ratio.
These ions form when water molecules act as both acids and bases, donating and accepting protons.
Fill in the blank:
The chemical equation for the autoionization of water is _______.
H₂O + H₂O ⇌ H₃O⁺ + OH⁻
This equation represents the reversible reaction of water molecules forming hydronium and hydroxide ions.
True or False:
The concentration of H₃O⁺ and OH⁻ is equal in pure water.
True
In pure water, both ions are present in equal concentrations of 10⁻⁷ M at 25°C.
Define:
Kw
It is the autoionization constant of water, equal to [H₃O⁺][OH⁻].
It is calculated by multiplying the concentrations of H₃O⁺ and OH⁻ ions.
For pure water at 25°C: [H₃O⁺][OH⁻] = (10⁻⁷)(10⁻⁷) = 10⁻¹⁴.
How does the concentration of H₃O⁺ affect the pH of a solution?
Higher H₃O⁺ concentration decreases pH, making the solution acidic.
pH is the negative logarithm of H₃O⁺ concentration: pH = -log[H₃O⁺].
Fill in the blank:
When the concentration of OH⁻ increases, the solution becomes more _____.
basic
Basic solutions have higher OH⁻ concentrations and lower H₃O⁺ concentrations.
What is the relationship between pKw and Kw?
pKw = -log(Kw)
At 25°C, pKw = 14.
How is pKw calculated?
pKw = pH + pOH
At 25°C, pH + pOH = 14.
Give a factor that affect the value of Kw.
Temperature
Kw is temperature-dependent and increases with rising temperature.
How is the pH scale range determined?
By taking the negative logarithm of Kw.
Kw = 10⁻¹⁴; pKw = 14, so the pH scale generally ranges from 0 to 14.
What happens to the concentrations of H₃O⁺ and OH⁻ when an acid is added to water?
H₃O⁺ concentration increases, OH⁻ concentration decreases.
Le Chatelier’s principle explains the shift in equilibrium to restore the product [H₃O⁺][OH⁻] = 10⁻¹⁴.
What is the pH of a solution where [H₃O⁺] = 1 × 10⁻⁵ M?
pH = 5
pH = -log[H₃O⁺], so pH = -log(1 × 10⁻⁵) = 5.
True or False:
The product [H₃O⁺][OH⁻] is always 10⁻¹⁴, regardless of solution conditions.
False
While Kw = 10⁻¹⁴ at 25°C, Kw varies with temperature.
List the ions present in a basic solution.
- Hydroxide ions (OH⁻)
- Some hydronium ions (H₃O⁺)
In a basic solution, OH⁻ ions outnumber H₃O⁺ ions, but both are present.
What is a dissociation constant?
It is the equilibrium constant for the dissociation of a substance in a solution.
The dissociation constant indicates how much of the substance dissociates into its ions at equilibrium.
What is Ka in chemistry?
Ka is the acid dissociation constant.
It is a measure of how much an acid dissociates in solution.
How is Ka used in acid-base equilibria?
Ka helps determine the strength of an acid and its dissociation in a solution.
Ka is a critical factor in determining how much an acid dissociates in water and its behavior in acid-base reactions.
True or False:
Strong acids always have Ka > 1.
True
A Ka > 1 indicates complete dissociation, characteristic of strong acids.
How is Ka calculated?
Ka = [H⁺][A⁻] / [HA]
This formula uses the concentrations of hydrogen ions (H⁺), conjugate base (A⁻), and the undissociated acid (HA).
What is the difference between strong and weak acids based on Ka?
- Strong acids: They have high Ka values.
- Weak acids: They have low Ka values.
Strong acids dissociate completely, while weak acids dissociate partially, leading to different Ka values.
What is the relationship between Ka and pKa?
pKa = -log(Ka)
pKa is the negative logarithm of Ka, providing a different scale to express the strength of acids.
What is the Ka expression for acetic acid?
Ka = [H⁺][C₂H₃O₂⁻] / [HC₂H₃O₂]
The Ka measures the extent of acid dissociation in water.
Calculate the Ka for acetic acid if the concentration of H⁺ is 0.0006 M and that of the acid is 1.2 M.
Ka = 3.0 x 10⁻⁷
This calculation uses the concentrations of H⁺ and acetic acid at equilibrium to find the Ka value.
Ka = (0.0006)(0.0006) / 1.2 = 3.0 x 10⁻⁷
What is the relationship between pH and Ka for weak acids?
A lower pH indicates a stronger acid with a higher Ka.
pH measures the concentration of hydrogen ions, which is related to the dissociation constant of an acid.
