Topic 2 -Role of Water Flashcards
Remember to read over assumed knowledge rev. notes!
Do it BEFORE studying this topic
What is ampipathic?
parts of molecule have an affinity for water, others do not.
Water can act as both an …. and a ….
acid and a base
What properties does Hydrogen bonding give to water?
High MP, BP & heat of vaporisation
Any molecule that has a H atom directly attached to a …. or a …. is capable of H bonding
oxygen or a nitrogen
What property of H acceptor atoms allows them to form a bond w/ H?
They have a lone pair electron
H atoms covalently bonded to C atoms do not participate in H bonding. Why?
C is not electronegative enough to cause unequal sharing w/ H
What molecules can dissolve in water?
Charged biomolecules (Na+, Ca-) Uncharged but polar molecules (sugars e.g. hydroxyl groups) Alcohols, aldehydes, ketones and compounds containing N-H covalent bonds
Polar molecules (hydrophilic) are water soluble. T or F?
true
Non-polar molecules (hydrophobic) are water insoluble. T or F?
true. includes lipids & fats
Ampipathic molecules are water soluble & insoluble. T or F?
true
To achieve thermodynamic stability when placed in water, what do ampipathic compounds do?
Minimise amount of hydrophobic area exposed to water (polar solvent) by grouping together. This increases entropy.
Think micelles, lecture pages 8-10
The strength of hydrophobic interactions results from…?
increasing entropy in water molecules by exclusion from hydrophobic regions which provides the greatest thermodynamic stability.
=> Important for membrane formation & protein folding
Name the four types of non-covalent interactions which occur b/w biomolecules in aqueous solution.
Hydrogen bonds
Ionic interactions
Van der Waals interactions
Hydrophobic interactions
What is Keq? State the equation
equilibrium constant -gives the position of a reaction is fixed for any given chemical reaction at a specific temp.
[product] Keq = [reactant]
[C] [D] Keq = [A] [B]
Write the Keq (equilibrium constant) for the reversible ionisation of water.
What is the concentration of pure water at 25˚C?
[H+] [OH-]
Keq = [H2O]
[H2O] at 25˚C= 55.5M
State the equation for the ion product of water (Kw) at 25˚C
[H+] [OH-] = 1 x 10^-14 M^2
As the ion product of water is constant, whenever [H+] is greater than 1 x 10^-7, [OH-] must be…?
less than 1 x 10^-7
A proton donor (acid) and its corresponding proton acceptor (base) make up a …?
conjugate acid base pair
State the pH equation
-log [H+]
State the ionisation (dissociation) constant equation (Ka)
[H+] [A-]
Ka = [HA]
HA = acid A- = base
What is pKa?
The pH at which there is 50% ionisation so [HA]=[A] (acid=base)
The stronger the tendency to dissociate a proton, the stronger the acid and the lower its…?
pKa
State the pKa equation
-log Ka
Why do we use titrations?
to determine the amount of acid in a solution
When [HA]=[A-] the pH at this point is the same as the…?
pKa
What is a buffer and what is a buffer system made of?
A buffer are substances that resist changes in pH
A buffer system is made of a weak acid (proton donor) and its conjugate base (proton acceptor).
State the Henderson-Hasselbach equation and what it tekks us
[A-]
pH = pKa + log [HA]
Describes the relationship b/w the pKa & pH of a weak acid
