5. Acids, Bases, and Solutions Flashcards
What is molality.
It is a unit of concentration consisting of moles of solute divided by the mass of solvent in kilograms. An advantage of using molality over molarity is that the mass is not affected by temperature or pressure. Therefore, concentrations in this unit remain invariant to these variables.
What is an electrolyte?
It is a substance that, as a result of dissociation into ions, conducts electrical current. Popular electrolytes include acids, bases, and salts that can be ionized in solvents, such as water or alcohol.
What is an acid and a base?
Acid: A substance that releases protons (H⁺) in water.
Base: A substance that releases hydroxide ions (OH⁻) in water.
What happens when a substance dissolves in water?
It forms a solute-solvent system.
Solute: The substance being dissolved.
Solvent: The substance doing the dissolving (e.g., water).
Some substances dissolve fully, while others only partially dissolve.
How is concentration measured?
Molarity (M) = moles of solute / liters of solvent.
Other units include:
Molality
% mass/mass
% volume/volume
What happens when a substance dissociates in water?
It breaks into ions, which are surrounded by water molecules.
Example: HCl → H⁺ + Cl⁻
Water prevents ions from recombining.
What is the Brønsted-Lowry definition of acids and bases?
Acid: A proton (H⁺) donor.
Base: A proton (H⁺) acceptor.
Example: HCl + H₂O → H₃O⁺ + Cl⁻
Water acts as a base by accepting H⁺.
What is the hydronium ion, and why is it important?
H₃O⁺ (Hydronium ion) forms when a water molecule accepts a proton (H⁺).
It makes solutions conduct electricity, making them electrolytes.
Strong electrolytes fully dissociate (e.g., HCl).
Weak electrolytes partially dissociate (e.g., acetic acid).
What is the difference between strong and weak acids/bases?
Strong acids fully dissociate in water (e.g., HCl).
Weak acids only partially dissociate (e.g., acetic acid).
Strong bases fully accept protons.
Weak bases only partially accept protons (e.g., NH₃).
What are amphoteric substances?
Substances that can act as both acids and bases.
Example: Water (H₂O) and Carbonic Acid (H₂CO₃).
What are conjugate acid-base pairs?
When an acid donates a proton, it forms a conjugate base.
When a base accepts a proton, it forms a conjugate acid.
Example:
Acid: Acetic acid (CH₃COOH)
Conjugate base: Acetate ion (CH₃COO⁻)
How does water behave in acid-base reactions?
Water is amphoteric (acts as both an acid and a base).
With a base → Water donates a proton (acts as an acid).
With an acid → Water accepts a proton (acts as a base).
What is water’s equilibrium constant (Kw)?
Water self-ionizes into H₃O⁺ and OH⁻.
Equilibrium expression: Kw = [H₃O⁺][OH⁻].
In pure water: [H₃O⁺] = [OH⁻].
How does adding an acid or base affect ion concentration in water?
Adding an acid increases [H₃O⁺] and decreases [OH⁻].
Adding a base increases [OH⁻] and decreases [H₃O⁺].
The product [H₃O⁺] × [OH⁻] = 1.0 × 10⁻¹⁴ remains constant.
What is the definition of an acidic and basic solution?
Acidic solution: [H₃O⁺] > [OH⁻]
Basic solution: [H₃O⁺] < [OH⁻]
What is pH and how is it calculated?
pH = -log [H₃O⁺]
pOH = -log [OH⁻]
pH + pOH = 14 (constant for water at 25°C).
What do pH values indicate?
pH < 7 → Acidic solution
pH = 7 → Neutral solution
pH > 7 → Basic solution
Why is pH used instead of [H₃O⁺]?
[H₃O⁺] values are very small, so using logarithms makes them easier to interpret.
Lower pH = Higher acidity, Higher pH = More basic.
What is the equilibrium constant for weak acid ionization?
Weak acids only partially ionize in water.
The equilibrium constant for acid ionization is Ka:
Ka = [H₃O⁺][A⁻] / [HA]
The larger the Ka, the stronger the acid.
What is the equilibrium constant for weak base ionization?
Weak bases only partially ionize.
The equilibrium constant for base ionization is Kb:
Kb = [OH⁻][HB⁺] / [B]
The larger the Kb, the stronger the base.
What factors determine acid strength?
Bond strength: Stronger bonds make it harder for H⁺ to dissociate.
Polarity: Greater electronegativity differences make acids stronger.
What is neutralization?
Neutralization is the reaction between an acid and a base to form water and salt.
This reaction counteracts pH changes.
What is an example of a neutralization reaction?
Strong acid + strong base:
HCl + NaOH → NaCl + H₂O
Weak acid + strong base:
CH₃COOH + NaOH → CH₃COO⁻ + H₂O
What happens when salts dissolve in water?
Salts from strong acids & strong bases → Neutral solution.
Salts from weak acids & strong bases → Basic solution.
Salts from strong acids & weak bases → Acidic solution.
What is metal ion hydrolysis?
Certain metal ions (e.g., Al³⁺, Fe³⁺, Cu²⁺) react with water to release H₃O⁺, making the solution acidic.
What is a buffer solution?
A buffer resists pH changes when small amounts of acid or base are added.
It consists of:
A weak acid or weak base
Its conjugate salt
Example: Acetic acid (CH₃COOH) + Sodium acetate (CH₃COO⁻Na⁺)
How do buffer solutions work?
If acid is added, the conjugate base neutralizes it.
If base is added, the weak acid neutralizes it.
Buffers are essential for biological and chemical stability.
What is titration?
Titration determines the concentration of an unknown acid or base using a known titrant.
A pH indicator (e.g., phenolphthalein) signals when the reaction is complete.
What happens at the equivalence point in titration?
Equivalence point: The amount of added base = amount of acid.
For strong acid & strong base: pH = 7.
For weak acid & strong base: pH > 7.
Solution color change occurs based on the indicator used.
What does a titration curve show?
Vertical axis: pH
Horizontal axis: Volume of titrant added
Steep section near pH 7: Small volume changes cause large pH shifts → High sensitivity.
How do we calculate acid concentration in titration?
Moles of acid = Moles of added base
Using volume and molarity, the unknown concentration can be determined.
What is solubility equilibrium?
Solubility equilibrium occurs when a solid dissolves in a liquid until the solution reaches its maximum solubility.
Beyond this point, additional solute will not dissolve.
What is the solubility product constant (Ksp)?
Ksp is the equilibrium constant for the dissociation of a salt in water.
It is calculated as the product of ion concentrations, raised to their stoichiometric coefficients.
How do we predict precipitation?
The ion product (Q) helps determine if a solution is unsaturated, saturated, or supersaturated.
Condition Meaning Result
Q < Ksp Unsaturated More salt can dissolve
Q = Ksp Saturated Solution is at equilibrium
Q > Ksp Supersaturated Excess salt precipitates
What happens in a supersaturated solution?
Supersaturated solution: More solute is dissolved than normally possible.
The extra solute precipitates to restore equilibrium.
How is solubility related to precipitation?
If Q > Ksp, precipitation occurs because there is too much solute.
If Q < Ksp, no precipitation occurs because the solution can still dissolve more solute.
