Unit 1 - Biochemistry

Water

Chemistry of Water

• H2O molecules form H-bonds with each other

• +H attracted to -O to create sticky molecule

(drawing of H2O molecule)

Special properties of Water

• cohesion and adhesion (difference between the two)

  • surface tension

• good solvent

  • molecules can dissolve in H2O

  • hydrophilic vs. hydrophobic

• lower density as a solid (ice floats)

• high specific heat (water stores heat)

• high heat of vaporization (heat & cools slowly)

Cohesion

• H2O molecules bond to other water molecules

  • water is “sticky” → surface tension

Adhesion

• water bonds to other things

  • capillary action

  • meniscus

  • water climbs up paper towel/absorbed by bath towels

Water is the solvent of life

• polarity makes H2O good solvent

  • polar H2O surround + and - ions

  • solvents dissolve solutes → solutions

• what dissolves in water?

  • hydrophilic (polar)

  • have attraction to H2O

• what doest’t dissolve in water?

  • hydrophobic (non-polar)

  • don’t have an attraction to H2O

Special case of Ice

• not more dense than when water is solid

• it floats (H bonds form crystal)

Why is ice floats important?

→ surface ice insulates water below (lakes don’t freeze solid), seasonal turnover of lakes (picture)

Specific Heat

• H2O resists changes in temperature

  • takes a lot to heat up

  • takes

Heat of Vaporization

• organisms rely on heat of vaporization to remove body heat

• Ionization of water and PH

  • H+ splits off form H2O leave OH-

  • if H+ = OH-, water is neutral, > water is acidic, < water is basic

  • pH scale (how acid or basic solution is) (water=7)

• pH of cells must be kept ~ 7

  • affects cellular function

• control pH by buffers

Chemistry