2.3

Water

• polar molecule

• Liquid - bonds form and break quickly, letting molecules move freely

• Solid - each molecule forms 4 hydrogen bonds, creating a rigid, open structure that makes ice less dense than water

Polar substance

hydrophilic (water loving) dissolve in water

Non-polar substances

hydrophobic (“water fearing”); do NOT dissolve in water

pH

• Water tends to split into H+ ions and OH− ions

• Pure water has equal concentrations of each

• Acids increase H+ concentration, bases decrease it

• Each pH unit represents ten-fold change in H+ concentration

pH importance

• affects enzyme function

• each microbe has an optimal pH range

• changes in pH can alter microbial communities