Chapter 2: water Flashcards
Water has what type of geometry?
Bent
How does the electrostatic attractions of water orientate themselves?
the O-H bond on one water molecule points towards a lone pair electron cloud on the oxygen of the other water molecule.
Electrostatic attractions cause what?
Hydrogen bonding
In genral how is a hydrogen bond repesented?
D-H….A where D-H is a weakly acidic donor such as N-H or O-H and A is a lone pair bearing and thus a weakly basic acceptor such as N or O
Hydrogen bonds are structurally characterized by an H…A distance of what?
atleast 0.5 A shorter than the calculated van der waals distance
What is Van der waals distance?
distance of closest approach between two non bonded atoms.
How does the energy of a hydrogen bond compare to the energy of a covalent bond energy?
Hydrogen bond energy is small
The central H2O molecule is what? and the others are what?
The central is the donor and the others are the acceptor.
Water does what upon freezing?
expands
Is frozen water more dense of less dense than liquid water?
Frozen water is less dense
Liquid water is only ____% hydrogen bonded than ice at 0 degrees C
15%
What does solubility depend on what?
ability of a solvent to interact with a solute more strongly than solute particles interact with eachother
water is an excellent solvent for what type of molecules?
Polar
Ions such as salts interact how?
According to columb’s law.
How do the dielectrical constants of water differ from that of nonpolar substances:
The dielectrical constant of water is among the highest while the dielectrical constant of nonpolar substances are relatively small.
How is the forces of ions in water different than the forces of ions with same conditions just in a nonpolar substance?
Since the D constant in water is higher than in nonpolar substances the force is water will be lower than the force in nonpolar substances.
In nonpolar solvents (low D constant) what happens to ions?
ions of opposite charge attract each other so strongly they coalesce to form salt
In water (high D) what happens to ions?
There is weaker force between the ions in water solution which permits significant quantities of the ions to remain separated.
When is an ion said to be solvated?
When an ion in a polar solvent attracts the oppositely charged end of the solvent dipoles. The ion is thereby surrounded by several concentric shells of orientated solvent molecules. which are then said to be solvated
The electric field produced by solvent dipoles do what?
oppose that of the ion so in effect the ionic charge is spread over the volume of the solvated complex.
Why do polar solvents have high dielectrical constants?
The electrical field produced; electrical field opposes that of the ion so in effect the ionic charge is spread over the volume of the solvated co
The orienting effect of ionic charges on dipolar molecules is opposed by what?
thermal motions with continually tend to randomly orientate all molecules thus dipoles in solvated complex are only partially orientated
Why is the D constant higher for water than for other polar substances with comparable dipole moment’s?
liquid’s water hydrogen bond structure permits it to form orientated structures that resist thermal randomization, thereby more effective distributing ionic charges.
Solubilities of polar and ionic substances are in enhanced if what?
Carry functional groups that can form hydrogen bonds with water such as
- Hydroxyl (-OH)
- Keto (-C=O)
- Carboxyl (-CO2H or COOH)
- or amino (-NH2)
