Acids and Bases Flashcards

Interactive active recall cards for pH calculations, weak acids Ka, buffer systems, and titration curves.

Bronsted-Lowry Theory & pH: read all 6 questions and answers

Define a Brønsted-Lowry acid.
A substance that acts as a proton (H⁺) donor.
Define a Brønsted-Lowry base.
A substance that acts as a proton (H⁺) acceptor.
What is a conjugate acid-base pair?
Two species that differ from each other by a single proton (H⁺). When an acid loses a proton, it forms its conjugate base.
Write the formula relating pH to hydrogen ion concentration, [H⁺].
\(\text{pH} = -\log_{10}[\text{H}^+]\).
Write the formula relating [H⁺] to pH.
\([\text{H}^+] = 10^{-\text{pH}}\).
Write the equation for the ionic product of water, \(K_w\).
\(K_w = [\text{H}^+][\text{OH}^-]\).

Weak Acids & Dissociation: read all 6 questions and answers

What is the standard value of \(K_w\) at 298 K?
\(K_w = 1.00 \times 10^{-14}\text{ mol}^2\text{ dm}^{-6}\).
Why is pure water always neutral, even if its temperature (and \(K_w\)) changes?
Pure water is neutral because the concentration of H⁺ ions always equals the concentration of OH⁻ ions ([H⁺] = [OH⁻]).
Write the expression for the acid dissociation constant, \(K_a\), for a weak acid HA.
\(K_a = \frac{[\text{H}^+][\text{A}^-]}{[\text{HA}]}\).
Write the relationship between \(K_a\) and \(\text{p}K_a\).
\(\text{p}K_a = -\log_{10}(K_a)\), and \(K_a = 10^{-\text{p}K_a}\).
What simplification is made to calculate the pH of a weak acid, HA?
Assume [H⁺] = [A⁻] (so \(\frac{[\text{H}^+]^2}{[\text{HA}]} = K_a\)) and that dissociation is negligible (so equilibrium \([\text{HA}] = [\text{HA}]_\text{initial}\)).
State the formula to calculate [H⁺] for a weak acid solution using \(K_a\).
\([\text{H}^+] = \sqrt{K_a \times [\text{HA}]}\).

Buffers & Titration Curves: read all 6 questions and answers

What is a buffer solution?
A solution that minimises pH changes when small amounts of acid (H⁺) or base (OH⁻) are added.
What are the components of an acidic buffer solution?
A weak acid and a salt of its conjugate base (e.g. ethanoic acid and sodium ethanoate, CH₃COOH and CH₃COONa).
Describe the buffer action when a small amount of H⁺ is added.
Added H⁺ ions react with the conjugate base (A⁻) in the buffer to form the weak acid (HA): A⁻ + H⁺ → HA, removing H⁺ from solution.
Describe the buffer action when a small amount of OH⁻ is added.
Added OH⁻ ions react with the weak acid (HA) in the buffer to form H₂O and conjugate base (A⁻): HA + OH⁻ → A⁻ + H₂O.
What is the equivalence point of a titration?
The point in a titration where the volume of reactant added is exactly stoichiometrically equal to the substance in the flask.
What is the half-equivalence point in a weak acid titration, and what is its significance?
The point where exactly half of the weak acid has been neutralised. At this point, [HA] = [A⁻], which means \(K_a = [\text{H}^+]\) and \(\text{pH} = \text{p}K_a\).