Water and pH in Biochemistry: Key Concepts and Buffer Systems

What percentage of body weight is total body water in adults?

Roughly 50 to 60%

How does body fat affect the percentage of body water?

Obese individuals tend to have a lower percentage of body water than thin individuals.

What are the two main compartments of body water?

Intracellular (60%) and extracellular (40%)

What does extracellular water include?

Fluid in plasma and interstitial water

What causes dehydration in the body?

When salt and water intake is less than the combined rates of renal and extrarenal volume loss.

Why is water considered an excellent solvent?

Due to its dipolar structure and ability to form hydrogen bonds.

What role does water play in chemical reactions?

Water is an excellent nucleophile, participating in many chemical reactions.

What is the dielectric constant of water?

78

How does water's high dielectric constant affect ionic bonds?

It decreases the force of attraction between charged particles, enabling water to dissolve salts.

What is a nucleophile?

A species that forms a chemical bond by donating bonding electrons.

How can water act as both an acid and a base?

It can donate protons (acting as an acid) or accept protons (acting as a base).

What are the three types of primary bonds?

Ionic, metallic, and covalent.

What characterizes ionic bonding?

One atom gives an electron to another, creating charged atoms that attract each other.

What is unique about metallic bonding?

Electrons in outer shells are shared among all atoms in a lattice, allowing for good thermal and electrical conductivity.

What defines a hydrogen bond?

The attractive force between one electronegative atom and a hydrogen atom covalently bonded to another electronegative atom.

What is a covalent bond?

A bond involving the sharing of electron pairs between atoms.

What are Van der Waals bonds?

Bonds formed from electrostatic charges in adjacent atoms, often present in polymers.

What is hydrolysis?

The process where nucleophilic attacks by water cleave amide, glycoside, or ester bonds.

How are acids defined in terms of protons?

proton donors.

What distinguishes strong acids from weak acids?

Strong acids completely dissociate in solution, while weak acids only partially dissociate.

What is pKa?

The negative logarithm of the dissociation constant (Ka) of an acid.

What happens to the dissociation constant as pKa decreases?

The tendency to dissociate into ions increases.

What is the nomenclature for undissociated acids?

They usually end in 'ic acid' (e.g., acetoacetic acid).

What is a diprotic acid?

An acid with more than one dissociable hydrogen ion, where dissociation is influenced by pH.

What do diprotic and triprotic acids have?

Multiple pKa values.

What is the dissociation constant of water (Kw) at 25°C?

1 x 10^-14 (mol/L)².

What is the concentration of H3O+ and OH- in pure water at 25°C?

Both are 1 x 10^-7 mol/L.

What is the relationship between pH and pOH?

pH + pOH = 14.

What does the pH scale measure?

The concentration of hydrogen ions (H+) in a solution.

What is the pH of pure water at 25°C?

7.0.

How is pH calculated from hydrogen ion concentration?

-log [H+].

What is the pH of a solution with a hydrogen ion concentration of 0.0001?

pH = 4.

What is the formula for calculating pOH?

pOH = -log [OH-].

What is the pH of a solution with a hydroxide ion concentration of 4.0 x 10^-4?

pH = 10.6.

What is the Henderson-Hasselbalch equation used for?

To relate pH to the dissociation constant of an acid (Ka) and the concentrations of its conjugate base and acid.

What is the equation derived from the Henderson-Hasselbalch equation?

pH = pKa + log [A-]/[HA].

What is buffering in a solution?

The ability of a solution to resist changes in pH when acids or bases are added.

What is the principal extracellular buffer?

Bicarbonate, which comprises carbonic acid and bicarbonate ions.

What physiological systems help maintain blood pH?

The kidneys and lungs.

What is the normal pH range of arterial blood?

7.35 to 7.45.

What happens to Kw at lower temperatures?

Kw decreases.

What happens to Kw at higher temperatures?

Kw increases.

What defines the strength of an acid in relation to pKa?

The stronger the acid, the lower its pKa value.

What is the auto-ionization of water?

2 H2O ⇌ H3O+ + OH-.

What is the significance of the log transformation in acid-base calculations?

It allows for the conversion of concentrations into a manageable scale for pH and pOH.

What is the buffering capacity of a solution?

Maximum buffering capacity occurs ± 1 pH unit on either side of pKa.

What is the role of acetic acid in buffer systems?

It can neutralize added acids or bases by converting to its conjugate base, acetate.