1. Water Flashcards
What characteristic of water made life evolve in it?
protection from UV light
high heat of vaporization
What type of environment do chemical reactions occur in?
aqueous
What is a critical determinant of the structure and function of proteins, nucleic acids, and membranes?
water
What is the octet rule?
four electron pairs around an oxygen atom in water
What is the structure of a water molecule?
two electron pairs covalently link two hydrogen atoms to a central oxygen atom and two pairs remain nonbonding
What molecular shape is water?
distorted tetrahedron
What is the electronegativity of the two hydrogen atoms in a water molecule?
positive dipole moment
What is the electronegativity of the two nonbonding pairs in a water molecule?
negative dipole moment
Define a hydrogen bond
electrostatic attraction between the oxygen atom of one water molecule and the hydrogen of another
When is the hydrogen bond the strongest?
when the bonded molecules allow for linear bonding patterns
Can water serve as a H donor or acceptor?
yes, both
How do water molecules interact with each other?
through hydrogen bonding
What properties does hydrogen bonding give water?
high boiling and melting point, large surface tension
What are the properties of hexagonal ice?
organized lattice and low entropy
Why is ice less dense than water?
hexagonal ice has maximal hydrogen bonds which forces the water molecules into equidistant arrangement
What is the max amount of hydrogen bonds able to be formed per molecule?
four
What are the four reasons H bonds are important?
- source of unique properties of water
- structure and function of proteins, DNA, and polysaccharides
- binding of substrates to enzymes and hormones to receptors
- matching of mRNA and tRNA
Water is a good solvent for what type of substances?
charged and polar
Water is a poor solvent for what type of substances?
nonpolar
What type of situation do hydrogen bonds readily form between?
electronegative atom and a hydrogen atom covalently bonded to another electronegative atom
What is a polar molecule?
negative on one side and positive on the other
What is a nonpolar molecule?
contains no polar charges
Will nonpolar gases be soluble in water?
no
Define noncovalent interactions
don’t involve sharing a pair of electrons
What are the four types of noncovalent interactions?
ionic
dipole
van der waals
hydrophobic effect
Define ionic interactions
electrostatic attraction between oppositely charged ions
Define dipole interactions
electrostatic interactions between uncharged but polar molecules
Define Van der Waals interactions
weak interactions between all atoms
Define hydrophobic effect
ordering of water molecules around nonpolar substances
What is the strongest noncovalent interaction?
ionic
What does it mean when ions are hydrated?
water molecules cluster about the ions
What effect do nonpolar compounds have on hydrogen bonding among water molecules?
increase enthalpy and decrease entropy
Is the free energy change for dissolving a nonpolar solute in water favorable or unfavorable?
unfavorable
How are the factors in the free energy change affected by dissolving a nonpolar solute in water?
Delta H will be positive
Delta S will be negative
Delta G will be positive
What shape does water form when interacting with nonpolar solute molecules?
cage like shell around each nonpolar solute molecule
What has to happen in order to dissolve salts?
break the ionic interactions
What happens to the ions when salt is dissolved?
they are hydrated
Are polar molecules hydrophilic or hydrophobic?
hydrophilic
Are nonpolar molecules hydrophilic or hydrophobic?
hydrophobic
What is an amphipathic molecule?
has polar and nonpolar areas
How does the hydrophobic effect work?
nonpolar portions of amphipathic molecules gather inward and polar portions are exposed
Why do amphipathic molecules follow the hydrophobic effect?
to form an energetically favorable statae
What effect do enzymes and receptors follow?
hydrophobic effect
What happens to the water when enzymes and receptors bind following the hydrophobic effect?
they displace the water
What are the two portions of Van der Waals interactions?
attractive and repulsive forces
How do attractive Van der Waals forces work?
at longer distances, depend on size of polarizability
How do repulsive Van der Waals forces work?
at very short distances, depends on size of atoms
What are the two reasons for using Van der Waals interactions?
they occur between any two atoms near each other and together they are strong
What do noncovalent interactions dictate?
macromolecular structure that affects function
What are colligative properties of water?
properties that depend on the concentration of the solute
What are three examples of colligative properties?
boiling point, melting point, and osmolarity
What are noncolligative properties?
properties that depend on the chemical nature of the solute
What are four examples of noncolligative properties?
viscosity, surface tension, taste, color
Colligative and noncolligative properties depend on what?
solutes
What produces osmotic pressure?
movement of water from higher to lower concentration
What is osmotic pressure?
force necessary to resist water movement
What is the van’t Hoff equation?
icRT
What is the van’t hoff factor?
measure of the extent to which the solution dissociates into 2+ ionic species
What is the van’t hoff factor for non-ionizing solutes?
1
What is the van’t hoff factor for solutes that dissocite into two ions?
2
What three things does osmotic pressure depend on?
van’t hoff factor, solute’s molar concentration, R and T
Define osmosis
water movement across a semipermeable membrane driven by differences in osmotic pressure
Define isotonic
equal amount of solutes inside and outside of cell
What direction is the water moving in an isotonic solution?
no water movement
Define hypertonic
higher concentration outside of cell
What is the water movement of a hypertonic solution?
water moves out of cell
Define hypotonic
higher concentration of solute inside the cell
What is the water movement in a hypotonic solution?
water moves into cell
