Unit 8: Topic 1 - Introduction to Acids and Bases Flashcards
What is the Arrhenius definition of acids and bases?
Arrhenius acids increase the concentration of H⁺ (hydrogen ions) in an aqueous solution. H⁺ ions immediately react with water molecules to form H₃O⁺ (hydronium ions).
For example, HCl can be defined as an Arrhenius acid, since it yields H⁺ ions in an aqueous solution: HCl -> H⁺ + Cl⁻
Arrhenius bases increase the concentration of OH⁻ (hydroxide ions) in an aqueous solution.
For example, NaOH can be defined as an Arrhenius base, since it yields OH⁻ ions in an aqueuous solution: NaOH -> Na⁺ + OH⁻
In a neutralization reaction, an Arrhenius acid and base react to form water and a salt: HCl (aq) + NaOH (aq) -> NaCl (aq) + H₂O (l)
What is the Bronsted-Lowry definition of acids and bases?
Bronsted-Lowry acids donate H⁺, while Bronsted-Lowry bases accept H⁺.
In the general reaction HA + B -> HB⁺ + A⁻, HA acts as an acid by donating H⁺ to B, which acts as a base, accepting the H⁺ ion to form HB⁺. HB⁺ is the conjugate acid, and A⁻ is the conjugate base.
How do we calculate pH and pOH?
pH is a measure of the concentration of hydronium ions ([H₃O⁺]) in a solution.* The lower the pH, the more acidic (or less basic) the solution is, and thus, the higher the concentration of hydronium ions. Conversely, the higher the pH, the less acidic (or more basic) the solution is, and thus, the lower the concentration of hydronium ions.
pOH is a measure of the concentration of hydroxide ions ([OH⁻]) in a solution. The lower the pOH, the more basic (or less acidic) the solution is, and thus, the higher the concentration of hydroxide ions. Conversely, the higher the pOH, the less basic (or more acidic) the solution is, and thus, the lower the concentration of hydroxide ions.
pH = -log[H₃O⁺] = 14 - pOH
pOH = -log[OH⁻] = 14 - pH
*pH is also conventionally defined as a measure of the concentration of hydrogen ions. Hydrogen ions do not exist in aqueous solutions, but instead take the form of H₃O⁺ (hydronium ions) as they bond with water.
How do we calculate [H₃O⁺] and [OH⁻]?
[H₃O⁺] = 10^-pH
[OH⁻] = 10^-pOH
What is the autoionization of water?
The autoionization of water is represented by the equation H₂O (l) + H₂O (l) <-> H₃O⁺ (aq) + OH⁻ (aq). One water molecule donates a proton, acting as a Bronsted-Lowry base, while another water molecule accepts the proton, acting as a Bronsted-Lowry acid. Thus, water is amphiprotic, or amphoteric, which means it can act as either an acid or a base.
The equilbrium constant, or autoionization constant, of the autoionization of water is Kw = [H₃O⁺][OH⁻] = 1.0 × 10⁻¹⁴ at 25°C.
What are some properties of the autoionization of water?
At 25°C, the autoionization of water is a neutral solution, which means [H₃O⁺] = [OH⁻] = 10⁻⁷ M. Thus, the pH and pOH of pure water at 25°C is 7. Since Kw = 1.0 × 10⁻¹⁴ at 25°C, we can find pKw: pKw = pH + pOH = 14 at 25°C.
What happens to the pH of pure water as temperature changes?
As temperature increases, the pH and pOH of pure water decreases. However, this does not mean the water becomes more acidic or basic at higher temperatures; it remains neutral, as [H₃O⁺] = [OH⁻].
If [H₃O⁺] = [OH⁻], then the solution is neutral.
If [H₃O⁺] > [OH⁻], then the solution is acidic.
If [H₃O⁺] < [OH⁻], then the solution is basic.
