Water Science Quiz

Water

• Water is a vital substance for life, making up a significant portion of most organisms.
• The human body consists of approximately 60% water predominantly found in extracellular fluids (surrounding cells) and within cells.
• Water's unique properties result from its polar nature, with the oxygen atom carrying a partial negative charge (δ-) and the hydrogen atoms bearing a partial positive charge (δ+).
• This polarity enables water molecules to form hydrogen bonds with each other and other molecules containing N-, O-, or S-containing functional groups.
• Hydrogen bonds are primarily electrostatic attractions, but also exhibit some covalent characteristics, creating a preferred orientation and directionality.
• Each water molecule can potentially participate in four hydrogen bonds, contributing to its unusual properties.

Properties of Water

• Water remains liquid at biologically relevant temperatures, allowing organisms to interact with it, live in and on it, and utilize it as a solvent.
• Water exhibits its highest density at 4°C, causing ice to float.
• Water has a high latent heat, meaning a large amount of heat energy is required to change its state from liquid to gas.
• Water serves as an excellent thermal buffer due to its high specific heat capacity, enabling it to absorb and release heat without drastic temperature changes.
• Water molecules exhibit cohesion, sticking to each other, and adhesion, adhering to other surfaces.
• This cohesion and adhesion contribute to water's high surface tension.
• Water is an excellent solvent, readily dissolving many substances, and can also act as a reactant in various chemical reactions.

Acids, Bases, and pH

• Pure water exhibits a slight tendency to ionize, resulting in small concentrations of H+ and OH- ions.
• The ionization of water is described by the dissociation constant, Kw, which indicates the relative concentrations of hydrogen and hydroxide ions.
• At neutral pH, the concentration of H+ ions equals that of OH- ions, having a value close to 10−7 mol L−1 at 25 °C.
• Acidic solutions contain a higher concentration of H+ ions (pH < 7), while basic solutions have a lower concentration of H+ ions (pH > 7).
• pH is a logarithmic scale, meaning a one-unit change in pH corresponds to a ten-fold change in H+ ion concentration.
• The physiological pH of human blood is near-neutral, ranging from 7.1 to 7.4.

Classification of Substances Based on pH

• Acids release H+ ions in solution, acting as proton donors.
  • Strong acids ionize almost entirely in water, releasing their hydrogen ions completely.
  • Weak acids ionize partially in water, not releasing all their hydrogen ions.
• Bases release OH- ions in solution or accept protons.
  • Strong bases ionize almost entirely in water, releasing their hydroxide ions completely.
  • Weak bases ionize partially in water, not releasing all their hydroxyl groups.
• Amphoteric substances can act as both acids and bases, such as water and amino acids.

Importance of pH in Body Fluids

• Blood pH: 7.1 - 7.4 (any change can be fatal).
• Urine pH: 6.8 (slightly acidic), with changes influencing the solubility of salts and potentially leading to urinary stones.
• Gastric juice pH: 1.5 - 2 (highly acidic), with increased acidity potentially causing peptic ulcers and decreased acidity resulting in hypoacidity.

Acidosis and Alkalosis

• Acidosis: Characterized by a low serum bicarbonate level (less than 22 mEq/liter).
  • Primary metabolic acidosis: Caused by diarrhea, carbonic anhydrase inhibitors, lactic acidosis, ketoacidosis in diabetes or alcoholism, and aspirin poisoning.
• Alkalosis: Characterized by an elevated serum bicarbonate level (greater than 29 mEq/liter).
  • Primary respiratory alkalosis: Occurs with hypocapnia (pCO2 < 35 mmHg) due to hyperventilation from anxiety, fever, or high altitudes.
  • Primary metabolic alkalosis: Caused by loss of gastric HCl without loss of pancreatic HCO3, such as vomiting, or administration of some diuretics.

Compensation Mechanisms for Acidosis and Alkalosis

• Respiratory acidosis or alkalosis: Compensated by the lungs, retaining or eliminating CO2.
• Metabolic acidosis or alkalosis: Compensated by the kidneys, retaining or eliminating HCO3-.