Water and Acids-Bases Quiz

Water, Acids-Bases, and Buffer Systems

• Learning Objectives: Recognize water structure, relate water structure to solubility, calculate concentrations in solutions, define acids and bases, and describe buffers.

Water

• Water's properties are crucial to biological molecule interactions. A thorough understanding of water's structure is vital.

• Total Body Water: Approximately 60% of an adult's body weight. Water is distributed between intracellular fluid (ICF) and extracellular fluid (ECF). Intracellular fluid (approximately 40% body weight) and Extracellular fluid (approximately 20% body weight).

• Water as a Universal Solvent: Water dissolves and transports compounds in blood, plays a role in molecule movement within cells, separates charged molecules, dissipates heat, and takes part in chemical reactions.

Solubility

• Dipolar Nature: Water's dipolar nature is essential for its solvent function.

• Universal Solvent: Water's ability to dissolve many substances makes it a universal solvent.

• Ionic Substances: Water dissolves ionic substances by attracting cations (positive ions) and anions (negative ions) to opposing charges in water molecules.

• Polar Molecules: Polar molecules can interact with water molecules. Such substances are called hydrophilic (“water-loving”).

• Non-Polar Molecules: Non-polar molecules cannot interact with water and are called hydrophobic (“water-fearing”). These tend to clump together.

Structure of Water

• Water is a dipolar molecule due to oxygen's high electronegativity, which pulls electrons closer to it than the hydrogen atoms.

• Hydrogen Bonds: Hydrogen bonds form between water molecules, a crucial property in water's behavior.

Solutions

• Homogenous mixtures: Mixtures of two or more substances are considered solutions if they are homogenous.

• Solvent: The major component is the solvent; the minor component is the solute.

• Types of Solutions: Different combinations of gas, liquid, and solid substances can form solutions.

Factors Affecting Solubility

• Solute/Solvent: The type of solute and solvent influence solubility.

• Temperature: Temperature change often affects solubility.

• Pressure: Changes in pressure, especially relevant for gases dissolving in liquids, can impact solubility.

• Common Ion Effect: The presence of a common ion can affect solubility.

Factors Affecting Dissolving Speed

• Temperature: Higher temperatures generally increase dissolving speed.

• Particle Size: Smaller particles dissolve faster.

• Mixing: Stirring or mixing enhances dissolving speed.

Amount of Solute in a Solution

• Weight Percent (w/w): Weight of solute per 100 g of solution.

• Volume Percent (v/v): Volume of solute per 100 mL of solution.

• Weight/Volume Percent (w/v): Weight of solute per 100 mL of solution.

• Molarity (M): Moles of solute per liter of solution.

Acid/Base

• Acids: Substances that release hydrogen ions (protons).

• Bases: Substances that accept hydrogen ions.

• Amphoteric Substances: Substances that can act as both an acid and a base.

• Conjugate Acid-Base Pairs: Acids and their corresponding bases.

pH

• pH Definition: The negative logarithm of the hydrogen ion concentration. pH = -log₁₀[H⁺].

• Why use pH? It's a convenient scale for expressing the acidity or alkalinity of a solution.

pH and Biological Functions

• Biological systems maintain specific pH ranges, critical for optimal function. Blood pH is specifically narrow in its range.

Buffer Systems

• Buffer Action: Buffers resist changes in pH when acid or base is added to a solution.

• Weak Acid/Conjugate Base or Base/Conjugate Acid: Buffer systems involve a weak acid and its conjugate base or a weak base and its conjugate acid.

Regulation of Blood pH

• Bicarbonate Buffer System: Critical for maintaining blood pH.

• Phosphate Buffer System: Another important system for blood pH.