Water Flashcards
What shape is water? What charges are on the molecules?
-Linear molecule w a bent shape - asymmetric distribution of electron density
-Highly electronegative oxygen pulls the electrons closer and gains partial neg charge so hydrogen has partial pos charge
-Unequal charge so considered polar
What are hydrogen bonds?
Strong dipole-dipole or charge-dipole interactions between a covalently cound hydrogen and lone pair of electrons
-Involve 2 electronegative atoms - nitrogen and oxygen
What does the possible 4 H-bonds per water molecule give water?
-Unusually high boiling point
-Uncharacteristically high melting point
-Unusually large surface tension
What is water a good or bad solvent for?
Good solvent for charged and polar sunbstances e.g amino acids and peptides, small alcohols, carbs
Poor solvent for nonpolar substances e.g nonpolar gases, aromatic moieties, aliphatic chains
Whta does the hydrophobic effect refer to and what is this a main factor behind?
Refers to the interaction of nonpolar molecules or components of molecules in aqueous solution
Main factors behind
-protein folding
-protein-protein association
-formation of lipid micelles
-binding of steroid hormones to their receptors
Does water surrounding nonpolar solutes have lower or higher entropy?
Low entropy
-This is thermodynamically unfavourable thus hydrophobic solutes have low solubility
What can occur with high enough concentrations of amphipathic molecules?
Complete aggregation into micelles - polar group on outside which can interact w water and non polar on the inside
Colligative vs non colligative properties
Colligative - boiling point, melting point, osmolarity - do not depend on nature of solute just concentration
Non colligative properties - viscosity, surface tension,taste, colour - depend on chemical nature of solute
What happens if a cell is in a hypertonic solution?
-Water moves out and cell shrinks
What happens if cell is in a hypotonic solution?
Water moves in, creating outward pressure, cell swells and may burst
What is the auto-ionization of water?
When hydrogen ions are spontaneously generated in pure water by dissociation (ionisation) of a small percentage of water molecules.
-dissociation of water is a rapid reversible process
What way can O-H bonds dissociate?
O-H bonds are polar amd can dissociate hetero-lytically
-Products are a proton and a hydroxide ion
What does the extent of water dissociation depend on?
Temperature
What happens proton ions in solution?
-Do not exist free in solution so rapily hydrated to form hydronium ions
What is a hydronium ion?
A water molecule w a proton associated w on eof the non-bonding electron pairs
Equilibrium constant
Keq = [H+][OH-] / [H2O]
What is Kw
Kw = [H+][OH-]
= 1x 10-14 M
In pure water……..
[H+]=[OH-] = 10-7 M
What is pH?
pH = -log[H+]
What are physiological buffers and what do they consist of?
-Solutions that resist changes in pH and maintain stable [H+] in biological systems
-When there are too many h+ ions, a buffer will absorb some of them, bringing pH back up and will donate H+ to reduce pH
-Consist of conjugate acid-base pair - acid base pair that differ by 1 proton
What is Ka?
A measure of the strength of an acid in solution or the extent to which it binds hydrogen ions (ionizes)
Ka = [A-][H+] / [HA]
What Ka does i) a strong acid and ii) a weak acid have?
Strong acid - Ka greater that 1
Weak acid less than 1
What is pKa
pKa = -logKa
-The lower the value of Ka, the higher the value of pKa
-The higher the value of pKa - the weaker the acid
-The larger the Ka, the stronger the acid
Henderson - Hasselbalch Equation for pH?
pH = pKa + log [A-] / [HA]
What pH do buffers function best in?
-pH corresponding to the pKa of the acid
Examples of important buffer systems in the body?
- Carbonic acid - bicarbonate buffer system
-maintain blood pH
-Acidosis - (HCO3) blood pH falls below 7.38
-Alkalosis - (CO2) blood pH rises above 7.42
2.Phosphoric acid - phosphate buffer system
-The second pka value of phosphoric acid is 7.21 which is around the physiological pH of 7.4
- The protein buffer system
