University:
Felician University
Course:
CHEM-001 | Basic Chemistry
Academic year:

2019
Views:

347

Pages:

2
Author:

5CelestialChronicle

Properties of Water Introduction Polarity refers to an uneven distribution of positive and negative charges within a molecule. One end of a water molecule has a slight positive charge (d+) and the other end has a slight negative charge (d–). This dipolarity causes adjacent water molecules to flip around so that the oxygen end of one water molecule is attracted to the hydrogen end of another. The molecules are connected by a hydrogen bond. The polarity of water explains its many properties: including solvation, cohesion versus adhesion, viscosity, buoyancy and thermal conductivity (water has a particularly high specific heat capacity). Water Transport Water is a solvent of polar substances (will dissolve), but is not a solvent of non-polar substances. This explains the way different chemicals are transported in blood plasma (roughly 90% water). Ions Ions (such as Na+ and Cl–) are charged particles, so they can freely dissolve in plasma. Water molecules surround the charged cations and anions and form hydration shells to separate them (polar associations are weaker than ionic bonds, but sufficiently large quantities of polar molecules can dissociate the ions). Glucose Monosaccharides (like glucose) are polar because they contain many OH groups (oxygen is electronegative). However, polysaccharides tend to be far less soluble as the individual sugars are far more likely to form hydrogen bonds with each other, which reduces the capacity for water to interact with the polymer (plus oxygen is lost during polymerisation). Amino Acids Amino acids vary in their polarity. Some have polar side chains, others have non-polar side chains. However, they are sufficiently soluble to dissolve in water because of the polarity of the amine (NH3+) and carboxyl (COO–) groups that form a backbone. The solubility of large proteins is dependent on the number and location of the non-polar amino acids. Cholesterol and Fats Cholesterol and fats (triglycerides) are non-polar and so will not dissolve in water (they are hydrophobic). They must be transported to the liver via lymph vessels, where they are packaged into a capsule with components that are polar (proteins and phospholipids). These complexes (lipoprotein or chylomicron) are water soluble and can be transported within the blood. Respiratory Gases The respiratory gases (oxygen and carbon dioxide) are both non-polar, however their solubility in water differs. Oxygen has low solubility in water and must be transported within the blood by haemoglobin (found in red blood cells). Carbon dioxide reacts with water to form carbonic acid, which is a polar substance. In the blood, the carbonic acid dissociates into bicarbonate ions (and hydrogen ions) for transport in the plasma.