water acids bases and buffer solutions

What is the bond angle between hydrogen atoms in a water molecule?

104.5 degrees (compared to 109.5 degrees in a perfect tetrahedron due to greater repulsion between lone electron pairs)

What is the length of the O-H bond in a water molecule?

Approximately 0.096 nm

How many hydrogen bonds can a single water molecule form in the liquid or solid state?

Up to 4 hydrogen bonds

How does the strength of hydrogen bonds compare to Van der Waals forces?

Hydrogen bonds are approximately 10 times stronger than Van der Waals forces

What is the molarity of pure water (density = 1 g/mL)?

55.5 M

What is the concentration of hydrogen ions in pure water at neutral pH?

1 x 10^-7 moles of H+ ions per liter (pH = 7.0)

What is the primary physiological buffer system that maintains human blood pH?

The carbonic acid - bicarbonate buffer system (H2CO3 / HCO3-)

What components make up a functional buffer solution?

A mixture of a weak acid and its conjugate base (or a weak base and its conjugate acid)

What is the pKa of acetic acid and what range defines its buffering region?

pKa = 4.76; buffering region extends from pH 3.76 to 5.76 (1 pH unit on either side of pKa)

At what point on a titration curve is the buffering capacity of a system maximal?

At the midpoint of the buffering region, where [weak acid] = [conjugate base] and pH = pKa

Which amino acid side chain has a pKa of 6.0, allowing proteins to act as effective buffers near neutral pH?

Histidine

Why is water generally not used as a reaction solvent in organic chemistry?

Because it does not dissolve organic reactants well and is both amphoteric and nucleophilic

What is the chemical definition of a solvent?

A substance that dissolves a solute to form a solution

What giving factor gives water its electrical dipole moment and makes it a polar molecule?

The electronegativity of oxygen (giving it a partial negative charge) combined with its bent tetrahedral structure

What types of biomacromolecules rely on hydrophobic interactions with water for proper folding and structure?

Proteins, DNA, and polysaccharides

What chemical equation represents the self-ionization (auto-ionization) of water?

2 H2O

What process splits liquid water into hydrogen and oxygen using electric current, and what is its energy requirement?

Electrolysis; requires 285.8 kJ/mol (15.9 MJ/kg)

What is the normal physiological pH range of human intracellular fluid (cytosol) versus blood, and what is stomach pH?

Cytosolic pH is ~6.8, blood pH is ~7.4, and stomach acid pH is 1 to 2

How do antacids work to relieve heartburn from excess stomach acid?

They contain buffering ions (usually carbonate) that absorb excess free hydrogen ions (H+) to moderate pH

What is the formula for calculating pH from hydrogen ion concentration?

pH = -log10[H+]

What equation mathematically relates pH, pKa, and the concentrations of a weak acid and its conjugate base?

The Henderson-Hasselbalch equation: pH = pKa + log([conjugate base] / [weak acid])

What happens when a strong base like NaOH is added to an acetic acid / acetate buffer system?

Hydroxide ions (OH-) react with hydronium ions, causing more acetic acid to dissociate into acetate and water to restore hydronium concentration