Acid-Base Chemistry Quiz

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Questions and Answers

What does the term 'concentration' specifically refer to in a solution?

The temperature of the solution

The number of solute particles in a given volume (correct)

The total mass of solute in the solution

The strength of the acid or base present

Which of the following accurately describes electrolytes?

They are solely acids and bases

They absorb electricity when dissolved

They dissociate into ions in solution (correct)

They do not conduct electricity in solution

What is the pH of a neutral solution at 25°C?

7 (correct)

What is the expression that represents the ionic product of water (Kw)?

Kw = [H3O+][OH-] Signup and view all the answers

How does the self-ionisation of water affect its classification as an electrolyte?

Because it forms very few ions Signup and view all the answers

How is pH defined mathematically?

pH = -log10[H3O+] Signup and view all the answers

What happens to the value of Kw as temperature increases?

Kw increases Signup and view all the answers

At 25°C, what is the concentration of hydroxide ions ([OH-]) in pure water?

$10^{-7}$ mol L-1 Signup and view all the answers

What is the relationship between pH and pOH at 25°C?

pH + pOH = 14 Signup and view all the answers

Which of the following substances can act as both an acid and a base?

Water Signup and view all the answers

What happens to pH when an acid is added to a buffer solution?

pH remains relatively stable Signup and view all the answers

What is a primary function of buffers in biological systems?

To maintain pH stability Signup and view all the answers

Which reaction represents how acetic acid in a buffer neutralizes added hydroxide ions?

HC2H3O2(aq) + OH−(aq) → C2H3O2−(aq) + H2O(l) Signup and view all the answers

What is required for a substance to be considered amphoteric?

It must have an ‘H’ to donate and a free electron pair to accept Signup and view all the answers

Why do buffers have equal concentrations of a weak acid and its salt?

To effectively resist pH changes Signup and view all the answers

What would occur to blood pH if there is a significant surplus of H3O+ ions?

Blood pH would decrease Signup and view all the answers

What can be inferred about nitrous acid compared to ethanoic acid?

Nitrous acid is a stronger weak acid than ethanoic acid. Signup and view all the answers

How many dissociation constants does oxalic acid have?

Two, as it is a diprotic acid. Signup and view all the answers

Which of the following correctly describes a strong base?

It completely dissociates into metal ions and hydroxide ions in solution. Signup and view all the answers

What is essential to calculate the acid dissociation constant (Ka) of a weak acid?

The initial molar concentration of the acid and [H+] at equilibrium. Signup and view all the answers

What does the base dissociation constant (Kb) represent?

The ratio of the concentration of the conjugate acid times the concentration of hydroxide ions to the concentration of the base. Signup and view all the answers

What is true about the extent of a reaction at equilibrium?

It shows how much product is formed at equilibrium. Signup and view all the answers

According to Le Chatelier’s Principle, what happens when more reactant is added to an equilibrium system?

The equilibrium shifts to produce more products. Signup and view all the answers

What happens to the concentration of NH4+ when ammonia dissolves in water?

It is present in very low amounts Signup and view all the answers

How does increasing pressure affect a gaseous equilibrium system?

It favors the direction that has fewer gas molecules. Signup and view all the answers

What is the relationship between Ka and Kb for a conjugate acid-base pair?

Ka × Kb = Kw Signup and view all the answers

What role does a catalyst play in an equilibrium reaction?

It speeds up the time taken to reach equilibrium without changing it. Signup and view all the answers

When does the equilibrium constant (Keq) not change?

When an inert gas is added to the system. Signup and view all the answers

How is pKa related to ionization in water?

Lower pKa values indicate greater ionization Signup and view all the answers

What does the equilibrium constant expression for the reaction aA + bB ⇌ cC + dD look like?

Keq = [C]^c[D]^d/[A]^a[B]^b Signup and view all the answers

What is the endpoint in a titration?

When the indicator changes colour Signup and view all the answers

What determines when an indicator changes colour in relation to pH?

The concentration of acid HIn equals that of its conjugate base In- Signup and view all the answers

What is the effect of cooling an exothermic reaction on its equilibrium?

It shifts the equilibrium toward the products. Signup and view all the answers

For an equilibrium system represented by 2SO2(g) + O2(g) ⇌ 2SO3(g), what happens to the ratio at equilibrium?

It becomes constant regardless of initial concentrations. Signup and view all the answers

Why is it important to select an appropriate indicator for titrations?

Indicators must change colour at the equivalence point Signup and view all the answers

What characterizes the dissociation of weak bases like ammonia?

They only dissociate slightly in water Signup and view all the answers

What can be inferred if the reaction quotient (QC) is greater than the equilibrium constant (KC)?

The reaction will proceed to the left. Signup and view all the answers

What occurs during the titration setup?

The titrant is known and added to a known volume of the analyte Signup and view all the answers

Which type of equilibrium constant, Kb, is associated with weak bases?

Concentration of products at equilibrium. Signup and view all the answers

What happens to the equilibrium constant (Keq) for an exothermic reaction if the temperature is increased?

It decreases. Signup and view all the answers

How does dilution affect an equilibrium system in solution?

It shifts the equilibrium to increase particles. Signup and view all the answers

Which factor does not affect the equilibrium constant?

Addition of a catalyst. Signup and view all the answers

If the reaction quotient (QC) is equal to the equilibrium constant (KC), what is concluded?

The system is at equilibrium. Signup and view all the answers

What occurs at the endpoint of a titration?

The indicator changes color. Signup and view all the answers

In a titration curve, what does the half-equivalence point indicate?

The volume of titrant added is half of the total required. Signup and view all the answers

How is a standard solution prepared?

By dissolving a primary standard in a measured volume of water. Signup and view all the answers

Which statement about the pH at the half-equivalence point is correct?

It is equal to the pKa of the acid. Signup and view all the answers

What is a common characteristic of a titration curve for a weak acid with a weak base?

Gradual pH change with no sharp increase. Signup and view all the answers

Which of the following describes a primary standard?

A pure substance used to prepare standard solutions. Signup and view all the answers

What is the general equation for a neutralization reaction?

Acid + Base → Salt + Water Signup and view all the answers

What is indicated by the pH at the equivalence point in a titration?

It can vary based on the strengths of acid and base. Signup and view all the answers

Study Notes

Chemical Equilibrium Systems

A system is any part of the universe being studied, such as an ocean or a test tube.
An open system interacts with its surroundings, allowing both energy and matter to move in and out.
A closed system only exchanges energy with its surroundings, not matter. Equilibrium in a closed system occurs when the rates of forward and reverse reactions are equal.

Chemical Equilibrium

Reactions can occur in both forward and reverse directions.
A system is at equilibrium when the forward and reverse reactions continue, but there are no further changes in concentration.
Physical changes are usually reversible, for example, the changes of state of water (ice, liquid, gas).
Many chemical reactions are also reversible in a closed system.

Reversible Reactions

A reversible reaction is one where the products can react to reform the reactants.
Forward and reverse reactions can happen simultaneously.
These reactions are shown using energy profile diagrams.
The rates of the forward and reverse reactions equal at equilibrium.
The reaction is in chemical equilibrium when the rates of the forward and reverse reactions are equal and the concentrations of the reactants and products remain unchanged.

Extent of Reaction

Different reactions proceed to different extents, meaning the ratio of reactants to products is different for each reaction at equilibrium.
The extent of a reaction describes how far the reaction goes in the forward direction when equilibrium is reached and how much product is formed.

Le Chatelier's Principle

If a stress is applied to a system in equilibrium, the system will shift to relieve the stress.
Items considered as stress are:
- Concentration
- Temperature
- Pressure

Effect of Temperature on Equilibrium Constant

The value of $K_{eq}$ depends only on the temperature.
For exothermic reactions, increasing the temperature shifts the equilibrium position to the left, causing $K_{eq}$ to decrease.
For endothermic reactions, increasing the temperature shifts the equilibrium position to the right, causing $K_{eq}$ to increase.

Equilibrium Constants

Chemists use numerical values to describe equilibrium positions.
The equilibrium constant, $K_{eq}$, relates the concentrations of reactants and products at equilibrium.
$K_c$ refers to concentration, and $K_p$ refers to pressures.