2) Introduction to Water Flashcards
Why is water molecule polar?
- O is more electronegative than H
- Unequal sharing/distribution of electrons
- Partial charges = polar molecule
What is the molecular shape of water molecule?
Bent
What is the typical bond angle of water?
109.5 degrees
List 5 physical properties of water
- Highly cohesive
- High heat capacity
- High boiling point
- Density of solid state less than liquid state
- High latent heat (heat of vapourisation)
What is cohesion? Give an example.
- Physical property of water molecules to remain closer together due to hydrogen bonds.
- e.g. Capillary action
Why does water have a high specific heat?
Much of the added energy is required to break hydrogen bonds.
Why is water’s high specific heat important?
- It allows for large amounts of heat to be absorbed with little change to its own temperature
- Therefore can act as energy sinks (like ocean)
Why does water have a high heat of vapourisation?
Due to hydrogen bonding - these bonds must be broken in order for water molecules to enter a gas phase.
What does amphipathic mean? Give an example
- Molecules with both hydrophilic & hydrophobic region
- e.g. carboxylate ion
What is evaporative cooling? Why does it happen?
Give an example.
- As water molecules evaporate, the surface gets cooler.
- This is due to molecules with the highest kinetic energy being lost due to evaporation.
- e.g. evaporation of sweat to maintain a steady temperature
Why is ice less dense than liquid water?
What is the significance of this?
- H bonds in ice form crystalline structure (hence more stable)
- Crystal = more spacious, molecules are forced further apart
- Hence less no. of molecules per unit volume = less dense
This is significant because ice forms on the surface of ponds and lakes = insulator
What is the significance of pKa relating to pH?
pKa value is the pH at which each ionisation form of a molecule is present at 50%
What is the isoelectric point? (pI)
The pH at which the molecule has NO net charge
What is the effect of changing pH on the activity of enzymes?
- Ionisation of acidic/basic amino acids
- This alters the bonds that determine the 3D shape of the protein
- Tertiary structure = protein function. Enzyme inactive or denatured
- The substrate cannot bind to the active site = cannot undergo catalysis
What is the concentration of H+ in pure water at room temp?
H+ = 1 x 10^-7 mol/L
