Acids & Bases Overview Quiz

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Questions and Answers

Which acid has the highest acidity based on its Ka value?

Hydrogensulphate ion (Ka = 1.2 x 10^-2)

Ethanoic acid (Ka = 1.8 x 10^-5)

Carbonic acid (Ka = 4.2 x 10^-7)

Sulphuric acid (Ka is very large) (correct)

What is the pKa value of Carbonic acid, given that Ka = 4.2 x 10^-7?

6.38 (correct)

5.38

7.38

4.38

Which of the following statements is true regarding pKa and acid strength?

pKa does not correlate with acid strength.

A higher pKa value indicates a stronger acid.

All acids have the same pKa value.

Lower pKa values represent stronger acids. (correct)

How does the dissociation of polyprotic acids differ from monoprotic acids?

Monoprotic acids exhibit complete dissociation. (C) Signup and view all the answers

What makes the second deprotonation of sulphuric acid (HSO4-) more difficult than the first?

It requires removing a proton from a negatively charged species. (C) Signup and view all the answers

What range of pH is optimal for a buffer solution to be effective?

pKa ± 1 (D) Signup and view all the answers

What is the primary factor influencing the amount of ionization of drug molecules?

The surrounding pH (D) Signup and view all the answers

How does the Henderson-Hasselbalch equation relate pH to pKa?

pH = pKa + log([base]/[acid]) (D) Signup and view all the answers

For which pH level is a phosphate buffer appropriate, given its pKa of 7.21?

Between 6.21 and 8.21 (C) Signup and view all the answers

What is the buffer capacity of a solution?

The amount of acid or base it can resist (B) Signup and view all the answers

What will happen to the absorption of a drug if it is in its ionized form in the stomach?

It will not be absorbed efficiently. (A) Signup and view all the answers

At what point is a drug most likely to be absorbed effectively in the gastrointestinal tract?

In the neutral environment of the small intestine (B) Signup and view all the answers

Which statement is true regarding the relationship between pKa and pH for a weak acid?

When pH = pKa, concentrations of acid and base are equal. (C) Signup and view all the answers

What distinguishes a strong acid from a weak acid?

A strong acid completely dissociates in solution while a weak acid only partially dissociates. (A) Signup and view all the answers

Which of the following statements is true regarding conjugate acids and bases?

Conjugate acids and bases exist in equilibrium with their parent molecules. (A) Signup and view all the answers

What is the primary role of water in the equilibrium `NH3 + H2O ↔ NH4+ + OH-`?

It acts as an acid. (B) Signup and view all the answers

What is the function of the equilibrium constant Ka?

It measures the dissociation of a weak acid in water. (D) Signup and view all the answers

How is the acidity of a weak acid related to its pKa value?

Smaller pKa values indicate weaker acids. (A) Signup and view all the answers

Which equation correctly describes the relationship between pKa and pKb?

pKa + pKb = Kw (C) Signup and view all the answers

What is depicted by the equilibrium constant Kb?

It measures the dissociation of a weak base in water. (D) Signup and view all the answers

What implication does a 0.00001M solution of HCl have?

It reveals that HCl is a strong acid despite being dilute. (B) Signup and view all the answers

Which of the following statements is accurate concerning strong and weak bases?

Strong bases completely dissociate in solution, while weak bases partially dissociate. (B) Signup and view all the answers

In the reaction of acetic acid with water, what is the conjugate base formed?

Acetate ion. (B) Signup and view all the answers

Study Notes

Acids & Bases, pH and Buffers

Blood pH levels range from 6 to 9, with 7.35-7.45 being the normal range; values outside this range indicate acidosis (low pH) or alkalosis (high pH).
Death can result from severe acidosis or alkalosis, as biochemical reactions are sensitive to pH.
Buffer solutions maintain a constant pH in biological systems, crucial for proper bodily function. Examples include saliva, sweat, blood, stomach, intestine, and urine.
The pH scale is logarithmic, meaning pH values change by powers of 10 (e.g., pH 1 is 10 times more acidic than pH 2).
The pH scale ranges from 0 to 14, with neutral pH = 7.
pH = -log[H+]
pOH = -log[OH-]
K_w= [H⁺][OH^-] = 1 x 10^-14

Learning Outcomes

Students should be able to explain acids, bases, pH, and pOH.
Students should be able to define strong and weak acids and their importance in biology.
Students should understand water auto-ionization.
Students should know about conjugate acid/base pairs (Ka, Kb, pKa, pKb)
Students should be able to calculate pH.
Students should explain buffer systems and the factors affecting choice of buffer, using the Henderson-Hasselbalch equation. and perform buffer calculations.

Biochemical Reactions in the Body

Biochemical reactions in the body are highly sensitive to pH.
Buffer solutions are crucial for maintaining this pH, and this includes saliva, sweat, blood, stomach, intestines, and urine.

Acids and Bases

Electrolytes, upon addition to water, dissociate into cations and anions.
Brønsted-Lowry Acid is a proton donor (HA → H⁺ + A^–).
Brønsted-Lowry Base is a proton acceptor (B + H⁺ → BH⁺).
Autoionization is a reaction between identical neutral molecules to form a cation and an anion (e.g., 2H₂O ⇌ H₃O⁺ + OH^-, Kw = [H⁺][OH^-]).

Equilibrium Constants

For any reversible reaction with reactants A & B and products C & D, the equilibrium constant is Keq = [C][D]/[A][B].
The water equilibrium is a reverse reaction (2H₂O ⇌ H₃O⁺ + OH^–), which lies predominantly to the left, implying a small degree of dissociation.
The equilibrium constant for water dissociation, K_w, is [H⁺][OH^-]/[H₂O]. However, the water concentration is assumed to be constant, therefore K_w = [H⁺][OH^-) = 1 x 10^-14 M².

pH

pH scale is a logarithmic scale expressing the concentration of H+ ions in solution.

Calculating pH

pH = -log[H+].

Strong/Weak Acids/Bases

Strong acids completely dissociate in solution, while weak acids only partially dissociate.
Strong bases completely dissociate in solution, while weak bases only partially dissociate.
Note: the strength of an acid or base is not dependent on concentration, but rather the equilibrium constant and pK values.

Conjugate Acids and Bases

A conjugate base is what remains of an acid after it has donated a proton.
- Weak acid dissociates to give H⁺ and its conjugate base.
- E.g. CH₃COOH + H₂O ⇌ H₃O⁺ + CH₃COO^- conjugate base.
A conjugate acid is formed when a base accepts a proton.
- E.g. NH₃ + H₂O ⇌ NH₄⁺ + OH^-.

Acid Equilibrium Constant

K_a = [H₃O⁺][A^-]/[HA]

Base Equilibrium Constant

K_b = [BH⁺][OH^-]/[B]

pKa, pKb

pK_a = -logK_a
pK_b = -logK_b

Polyprotic Acids

Polyprotic acids can donate more than one proton (e.g., H₂SO₄, H₃PO₄).
Each dissociation step has its own equilibrium constant.

Buffers

Buffer solutions resist changes in pH when an acid or base is added.
Often contain substances with acidic and basic forms (Conjugate pairs of weak acids).
The Henderson-Hasselbalch equation gives the relationship between pH, pKa, and the concentrations of the acid and its conjugate base. pH = pKa + log[base]/[acid].
Buffers work best around a pH range of ±1 of their pKa.

Choice of Buffer Solution

The choice of a buffer solution depends on the desired pH range. Biological fluids commonly use a phosphate buffer as it works well at slightly above neutral pH (e.g pH 7).

Acids & Bases in Biological Systems

Many biological processes require specific pH levels.
For example, the small intestine has a pH of around 6, to ensure proper functioning of digestive enzymes and absorption of nutrients.
The pH of the stomach is extremely low (1 to 2) to help break down food.
Certain drugs must be in a non-ionized form to be absorbed through cell membranes.
pKa's and ionisation play key roles in medicine absorption; for example, aspirin is better absorbed in the stomach.

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Description

Test your knowledge on acids, bases, pH, and buffers with this informative quiz. Learn about the importance of maintaining pH levels in biological systems and explore concepts such as water auto-ionization and the characteristics of strong and weak acids. Ideal for high school biology students and chemistry enthusiasts.