Lecture 3: Water Flashcards
what properties of water make it critical to life?
- covalent, very stable
- “universal” solvent
- thermal properties
- plays direct role in stability and behaviour of other molecules in the cell
- plays direct role in chemical reaction mechanisms
water forms a ___ shape due to ___ of lone pairs, it is __
tetrahedron; distorted tetrahedron
it is the polar nature of water that allows it to
interact with other charged/polar molecules to dissolve them
each water molecule can interact with up to __ other water molecules
4
____ explains why water is a cohesive liquid at room temp
hydrogen bonding
hydrogen bonds found to be less than the sum of ___
their van der waals radii
hydrogen bond strength increases with
increase in electronegativity
hydrogen bond formation in liquid water is a __ process. Each bond has a half life of about ____
dynamic; 10 pinoseconds
most water molecules at liquid phase are bound to __ other water molecules at any given time
1-2
the surface of the water is ___ molecules thick
one
the surface of the water is held in tension by
innumerable hydrogen bonds
why can an insect walk on the surface of the water?
the water molecules are more attracted to each than to the leg of the insect
water can evaporate below the boiling point if:
the air around is not 100% saturated with water
the thermal energy needed to break H bonds is taken from ___, which __
the liquid water, which cools it down
solid water forms a
cross-linked lattice
molecules in solid water are oriented so that ___, this provides__
H bonds form a straight line; maximum strength to each bond
why is solid water less dense than liquid water?
the lattice causes molecules to be pushed farther apart, which lowers the density
the transition from solid to liquid results from the breaking of __% of H bonds in ice
15-20
an odd property of water is that is is __ at room temp
liquid
compared to related molecules, water should have a melting point of ___ and a boiling point of __
-100’C and -91’C
water separates ions by ____ interacting through ___ interactions
electrostatically; charge-dipole
each ion being dissolved by water is surrounded by a __, which __
hydration shell of water; shields them from interacting with each other
the ability of water to shield ion charges is measured by its ___ or __
dielectric constant; relative permittivity
the dielectric constant of a solvent is a measure of its __
polarity
water has a ___ dielectric constant
very high
the lower the dielectric constant, the ___
less able it is to hydrate ions
energy of interaction
the energy required to separate 2 charged particles by countering the attractive electrostatic force bewteen them
water can dissolve other non-ionic molecules as long as they are
polar
hydrophobic molecules cannot dissolve in water because
theyre not ionic or polar
in the presence of hydrophobic molecule, how to water molecules react?
interact with each other, forming a cage around the molecule
a clathrate represents a ___ arrangement
highly ordered
a clathrate is thermodynamically ___ which causes the hydrophobic molecule ___ suddenly, reducing ___
unfavourable; coalesce; surface area contact to water
clathrate coalesce suddenly is a ___ driven process
entropy
the longer the HC chain the ___ soluble
less
the more polar groups per carbon the __ soluble
more
