Briefly describe the molecular structure of water
- it is polar - O-H = polar because O is much more electronegative than H. The O has a partial negative charge and the H has a partial positive.
H2O us a polar molecule but why??
- because it has a dipole L> dipole - dipole interaction = electrostatic interaction...+ and -...aka hydrogen bond...very strong and its non covalent (doesnt share electrons ) - geometry : its bent at 104.5....one side = negative (O) and the other = positive (H) L> linear structures are non polar...because the polarity cancels out...ex: CO2 (OdoublebondCdoublebondO)
Electrostatic interactions occur between?
- opposite charges(including partial charges on atoms in a polar bond)
Since H2O is polar....what will dissolve in it?
- all polar molecules
What are the three types of non covalent bonding?
Ionic interactions Hydrogen bonds Van der waals forces L> Dipole-dipole, Dipole-induced dipole and induced dipole-dipole interactins.
Explain ionic interactions
- opposites attract - likes repel - forms salt bridges
Explain hydrogen bonding!
- occurs between a hydrogen that is attached to an oxygen or nitrogen and a lone pair of electrons on O, N or S - each H2O molecule can form H bonds with four other H2O molecules - these aggregations of bonds explain waters high boiling point.....it requires a lot of energy to break these bonds
Broadly what are van der waals forces?
- relatively weak electrostatic interactions - occur between neutral or permeant/induced dipoles/ L> magnitude depends on how easily an atom is polarized L> electroneg atoms with unshared pair of e- = easiest to polarize - the larger the electro diff between atoms = larger polarity of bonds..
Types of Van der waals forces: 1. Dipole-dipole interaction? 2. Dipole-induced dipole interaction? 3. Induced dipole-dipole
1. between two molecules containing electroneg atoms....positive end is directed towards the negative end of another...these hydrogen bonds are very strong. 2. permanent dipole induces a transient dipole in another molecule via distorting its electron distribution. these are weaker than above. 3. motion of nearby electrons of non polar molecules results in transient charge imbalance in adjacent molecules. L> transient dipole in a molecule polarises the electrons of its neighbour..= london dispersion forces ...these are the weakest (DNA molecule stacking ex)
Thermal properties of water?
- high melting and boiling points via hydrogen bonding - high heat of vaporization...it doesn't boil easily - high heat capacity: water can absorb and store heat and release it slowly - organisms use hess to reg temp: high water content = easier time retaining heat via its high heat capacity and evaporation is used as a cooling system.
Polar molecules and ionic substances are hydrophilic/hydrophobic?
- hydrophilic (soluble in h2o)
shells of h2o formed by water around a elute L> depends on charge density...the smaller and more highly charged the ion, the larger the salvation sphere L> an ion with a larger salvation sphere moves more slowly. - they negate the charges - this occurs when a salt is added to water
Hydrophobic molecules are polar/nonpolar?
Why do hydrophobic molecules group together in water?
- water molecules max the formation of H bonds with other water molecules and min any association with the non polar molecules....via forming small cages around a group of non polar molecules
-contain both hydrophobic and hydrophilic ends - hydrophobic head and a long hydrophilic tail form micelles or bilayers
What is the formula for osmotic pressure?
L> describe what each variable is
-π= osmotic pressure
- i= degree of ioniztion (van't Hoff factor)
-R= 0.082 Latm/kmol
- T= temperature in Kelvin.... C+2173)
What is the formula for osmolarity?
- Osmolarity= iM
Ex problem for Osmolarity:
1. What is the osmolarity of a 0.5M solution of Na3PO4 assuming an 85% ionization for the solution?
Na3PO4----------> 3Na(+) + 1PO4 (-3)
Initial: 0.5M 0 0
85% ionization: 0.075M 1.275M 0.425M
above was done via: 0.5(.85) = 0.425M ........0.425(3)= 1.275M
Σ= 1.775oM= 1.8oM
having the same (or equal) osmotic pressure and same water potential since the two solutions have an equal concentration of water molecules.
Having a higher osmotic pressure in a fluid relative to another fluid.
Of or pertaining to a solution (e.g. extracelllular fluid) with higher solute concentration compared with another. (see: hypotonic, isotonic). For example, if the extracellular fluid has greater amounts of solutes than the cytoplasm, the extracellular fluid is said to be hypertonic.
having a lesser osmotic pressure in a fluid compared to another fluid, as in a ‘hypotonic solution’ – compare hypertonic, isotonic refers to a solution with a comparatively lower concentration of solutes compared to another
Cell membrane potential?
- cytoplasmic side of the cell mem is negatively charged due to charged amino acid R groups on proteins.....cells regulate thier osmolaeit usually by pumping ions across the membrane
What is the formula for pH
ph= -log [H]
1.0x10^-14 = neutral
- ph = 7 neutral
- ph> 7 ....= basic
What is a strong acid and Base?
- they do not completely dissociate in water
weak acid: HA H(+) + A(-)
H+ = conj base
What is the formula for the dissociation constant of acids and bases?
L> lower the ka the stronger the acid .....the higher = the weaker acid
L> this is for the loss of an H
- the stronger the acid the more dissociation.....aka more H in solution....
pka- -logKa....therefore the lower the pka the stronger the acid!
What is a buffer?
solution of a weak acid (HA) and its conjugate base (A-)
L> buffers resist pH changes when H or OH is added (Le Chatelier's principle)
- human blood falls below 7.35....
- ph in blood goes above 7.45
Buffering capacity depends on what?
- the total buffer concentration and ration of A-/HA
- total buffer concentration = HA+A-
ph= pKa+ log[A-]/[HA]
When are buffers most effective?
when A-=HA ....or in the pH range of +/- 1 pKa
- titration curves show relatively flat areas when the ph= pKa...these areas indicate good buffer ranges because a relatively large amaount of OH may be added with very little change in pH
Ex problem with buffers:
Calc the pH of a solution containing ten millimole of benzoic acid and one hundred millimoles of sodium benzoate. pKa of benzoic aci= 4.2
- 10mmol BA
- 100mmol SB
pka BA= 4.2
- pH= pKa+ log[A-]/[HA]
- ph = 4.2+ log[100mmol]/[10mmol]
pH of 300mL of 0.24M Sodium hydrogen ascorbate and 150mL of 0.2M HCl (pKa1 of ascorbic acid= 4.04) ?
first find moles:
Sodium Ascorbate: 0.24Mx0.300L = 0.075mols (conj base)
HCl= 0.2Mx0.150L= 0.030mols of strong acid
- Strong acid reacts with conj base.
HCl + NaHAsc H2Asc + NaCl
Initial: 0.030 0.075 0 0
equilibrium: 0 0.045 0.030 0.030
conj.base(NaHAsc)+ H2Asc (weak acid) = buffer
pH= 4.04 + log [0.045moles/0.45L]/[0.030moles/0.45L] = 4.22
Three types of physiological buffers?
1. Bicarbonate buffer
2. Phosphate buffer
3. Protein buffer
- CO2+ H2O H2CO3 H(+) + HCO3(-)
L> simplified: CO2 +H2O H(=) + HCO3(-) pKa= 6.37
What enzyme facilitates bicarbonate buffer?
- carbonic anhydrase
How can bicarbonate serve as a buffer in blood?
- both CO2 and HCO3- can be regulated by the lungs and kidneys...CO2 can be exhaled...and the kidneys remove H+ from the blood......both of these are needed to keep the ratio HCO3-/CO2 high
Why is the HCO3-/CO2 ration needed to be kept high at a pH of 7.4?
- because the buffer pH is more basic than its pKa ....the buffer needs more conj base than acid...alt we could us H-H equation ..giving us a 11:1 ratio.
- H2PO4(-) H(+) + HPO4(2-)
- pKa= 7.2
-the pKa is very close the pH of blood...why isn't H2PO4(-)/HPO4(2-) an importan buffer in the blood.
- the conc are too low.....phosphate buffers are importan in intracellular fluids where these concentrations are higher.
- some amino acid side groups are weak acids or bases so many protens can act as buffers to help regulate pH of the blood
How would you prepare 1 L of 0.20M lactate buffer with a pH of 4.2. What ratio of lactate salt to lactic acid wuld you use. pKa = 3.86
ph= pKa+ log[A]/[HA] A= salt...HA= acid
A + HA = 0.2M (we know this)
2.19(HA) + HA= 0.20
A= 2.19(0.063)= 0.14M
- to prep this buffer you need 0.14moles of lactate and 0.063 moles of lactic acid in 1L of water