Lecture 4: Water Polarity

True/False: Similar to most other substances, solid water is more dense than liquid water

False

Substances that reduce drastic changes to a solutions concentration of H+ and OH- are called _____.

Buffers

The reason that certain insects can walk on the surface of water is due to this property of water.

High Surface Tension

Why is water able to form densely-packed hydrogen bonds?

• Solid water is less dense than liquid water

• Water has two dipoles

• Water has a strong surface tension

• Water has a high boiling point

What is a Hydrophobic interaction?

Nonpolar molecules sequester away from water.

What is a Amphipathic interaction?

Molecules with both hydrophobic and hydrophillic groups arrange their hydrophobic groups together (away from water) and their hydrophillic groups together (towards water)

What is a Hydrophillic interaction?

Ionic and polar molecules dissolve and interact with water (saturation can occur).

Which chemical interactions fall in the nonpolar category?

• Induced Dipole-Induced Dipole

• Hydrophobic

Which chemical interactions fall in the polar category?

• Dipole-Dipole

• Ion-Dipole

• Hydrogen Bonding

• Hydrophillic

• Ionic Bond

• Salt Bridge

Which chemical interactions fall in the both nonpolar and polar category?

• Dipole-Induced Dipole

• Amphipathic

Define Cohesion.

Chemical interactions that hold many of a sole type of molecule together.

Define Adhesion.

Chemical interactions between different types of molecules help keep them in place.

Define Hydrogen Bonding.

When hydrogen is covalently bonded to a highly electronegative atom, it can interact with a hydrogen acceptor.

Define Surface Tension.

Interactions between molecules at the border of the substance provide resistance to stretching.

True/False: Since air has a higher specific heat than water, relatively warmer water is very effective at increasing the temperature of the air around it.

False

True/False: Solid water has a more organized structure (more crystalline) than liquid water because the lower energy status of the molecules allows for more stable hydrogen bonding.

True

Define a Solution.

Homogeneous liquid mixture.

Define a Solute.

Substance dissolved in liquid.

Define a Solvent.

Liquid dissolving agent.

What is a Buffer?

Combination of weak acid and conjugate base that resists changes in pH upon addition of strong acids and strong bases

What is pH?

The concentration of H+ ions in a solution.

How does pH effect Enzyme activity?

• Enzyme active sites often contain AA side-chains that fluctuate by pH

  • pH>pKa = Deprotonated

  • pH>pKa = Protonated

What properties of water that create a unique environment for biological interactions?

• Unique polarity

  • 2 dipoles 

  • Unexpected bond angle 

• High melting and boiling points (specfic heat) 

  • Ability to form many hydrogen bonds (surface tension) 

  • Allows life to exist across a range of temperatures 

  • Solid water > density vs liquid water 

• Creates unique environment for biological molecules 

  • Proteins, Lipids, Nucleic Acids