pH and Buffers

Questions and Answers

What property of water makes it effective as a solvent for ionic and polar substances?

Its high pH level

Its ability to form hydrogen bonds (correct)

Its temperature-regulating ability

Its strong dipole nature (correct)

What is the significance of the auto-ionization of water?

It maintains the pH balance in biological systems (correct)

It leads to the formation of strong acids only

It is irrelevant in physiological processes

It generates only hydroxide ions

Which of the following correctly describes the role of a buffer?

Buffers concentrate acids only

Buffers are always weak bases

Buffers perform neutralization between two strong acids

Buffers resist changes in pH (correct)

What is the ion product constant of water (Kw) at 25ºC?

1.0 x 10-14 M2 Signup and view all the answers

Which statement correctly defines a strong acid?

An acid that completely ionizes in solution Signup and view all the answers

How do hydrogen ions contribute to the pH of a solution?

By lowering the pH when their concentration increases Signup and view all the answers

What happens during the neutralization reaction between an acid and a base?

Water and salt are formed Signup and view all the answers

Which characteristic of water contributes to its high boiling point compared to other substances?

Extensive hydrogen bonding between water molecules Signup and view all the answers

What is the pH of a neutral solution at 25ºC?

7.00 Signup and view all the answers

Which ion concentration increases with a decrease in the concentration of the other ion according to the equilibrium principle?

[H+] increases and [OH-] decreases Signup and view all the answers

What is the physiological pH range for most body fluids?

6.5 - 8.0 Signup and view all the answers

Which of the following statements about strong acids is correct?

They completely dissociate in solution Signup and view all the answers

What is the pH of gastric acid?

0.70 Signup and view all the answers

How does the pH scale correspond to acidity and basicity?

pH < 7.00 is acidic, pH > 7.00 is basic Signup and view all the answers

What characteristic distinguishes weak acids from strong acids?

Weak acids only partially ionize in solution Signup and view all the answers

What substance serves as the most important buffer in the human body?

Bicarbonate Signup and view all the answers

Which of the following statements about pKa is true?

The smaller the pKa, the stronger the acid Signup and view all the answers

Study Notes

Buffers resist changes in pH by maintaining a stable concentration of hydrogen ions (H+) in solution.
Acid: H+ donor; Base: H+ acceptor; water (H2O) can act as both.
Ionization of water:
- H2O ⇄ H3O+ + OH−
- Ion product constant (Kw) at 25ºC: Kw = [H+] × [OH−] = 1.0 × 10^-14 M².
In pure water, [H+] = [OH−] = 10^-7 M, leading to a neutral pH of 7.0.

Properties of Water

Water is essential for life, providing a medium for biochemical reactions.
Strongly electronegative oxygen creates a strong dipole, making water a polar solvent.
Unique properties include high surface tension and elevated boiling point.

pH Scale and Measurement

pH is a logarithmic scale measuring [H3O+] concentration:
- pH = -log[H3O+].
Neutral solutions have a pH of 7.0; acidic solutions are < 7.0, and basic solutions are > 7.0.
Physiological pH range for most body fluids is 6.5 - 8.0; gastric juice has a pH of 1 – 3.

pH in Living Systems

Gastric acid: 0.70
Lysosomes: 4.50
Granules of chromaffin cells: 5.50
Urine: 6.00
Neutral H2O (at 37°C): 6.81
Cytosol: 7.20
Cerebrospinal fluid (CSF): 7.30
Blood: 7.34 – 7.45
Mitochondrial matrix: 7.50
Pancreas secretions: 8.10

Ionization of Acids and Bases

Strong acids completely ionize, while weak acids partially ionize in solutions.
Weak acids and bases establish equilibrium with their conjugate forms.
Dissociation constant (Ka) for acids:
- Ka = [H+] × [A−] / [HA]; pKa = -log(Ka).
A smaller pKa indicates a stronger acid.

Buffers

Buffers consist of a weak acid or a weak base and its salt.
They minimize pH changes upon the addition of small amounts of acids or bases.
Bicarbonate is a crucial buffer in the human body, maintaining physiological pH.

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Description

This quiz focuses on the concepts of pH and buffers as part of Year 2, Unit I. It explores the mechanisms by which buffers resist changes in pH, covering fundamental topics like acids, bases, and neutralization reactions. Ideal for students in medical biochemistry.