Water - Unique Properties

#review

Preface

• Water is a molecule that is essential to life, as it exhibits properties not found in other molecules, owing to its strong polarity and its prevalent hydrogen bonds

Unique Properties of Water

Cohesion-Adhesion

• Hydrogen bonds allow the water molecules to stick to each other or other molecles
  • Think: - Why do we get wet?

High Heat Capacity

• Water can absorb a lot of energy (enthalpy) without temperature increases.
  • Think: - How come water is used to extinguish fire?

High Heat of Vaporization

• High Latent Heat of Vaporization. Tons of energy needed for $H_2{O}_{(l)}\to H_2{O}_{(g)}$
  • Think: - Why does water stay so cool during the summer?

Low Density Solid

• Only type of liquid that becomes less dense when it becomes a solid
  • Think: - Why does ice float, and not sink into the water? (Less Mass)

Very Strong Solvent

• Molecules can easily dissolve in water.
  • Think: - Why do we mix salt into our soup?
• Hydrophilic - Organic molecules attracted to water (ie: Salt)
• Hydrophobic - Organic molecules repellent to water (ie: Oil)

Determines pH

• Organisms are very sensitive to pH.
  • Think: - Why are acids so dangerous for us?
• $H_2{O}_{(l)}\rightleftharpoons H_{(aq)}^{+}+O{H}_{(aq)}^{-}$ , $pH=-\log [H^{+}]$

Acid and a Base (Brønsted-Lowry)

• Water can either accept or donate a proton (Amphiprotic)
• Makes it an acid or a base
  • Think: Why is Water so important for pH?