Chapter 3- Water: The Matrix of life Flashcards Preview

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Flashcards in Chapter 3- Water: The Matrix of life Deck (41):

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 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 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 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)


Solvation spheres?

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


Amphipathic 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= iMRT 

-π= osmotic pressure

- i= degree of ioniztion (van't Hoff factor) 

-M= molarity 

-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.


Hypertonic ?

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 

ph<7= acidic


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? 

ka= [H+][A-]/[HA]

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) 


Acidosis? Alkalosis?

- 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- 


Henderson-Hasselbalch equation?

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= 5.2


Ex buffers: 

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


Bicarbonate 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 us a 11:1 ratio.


Phosphate Buffer??

-   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. 


Protein Buffer??

- 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

 4.2= 3.86+log[A]/[HA] 


2.19= A/HA 


A + HA = 0.2M (we know this) 

2.19(HA) + HA= 0.20 


Ha= 0.063M

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