Chapter 2 - Aqueous Chemistry Flashcards
what type of bonds are in a water molecule?
two covalent bonds between a central carbon and two hydrogen atoms
how many unshared electron pairs are in a water molecule?
two
electronic geometry of water? molecular geometry?
tetrahedral; bent
water polar or nonpolar? why>
polar, oxygen atom bears a partial negative charge and each hydrogen atom bears a partial positive charge; uneven distribution of charge
how do water molecules orient themselves?
partial positive hydrogen is aligned with partial negative oxygen, a hydrogen bond
how many hydrogen bonds can water participate in?
four, two hydrogen atoms to “donate” to a hydrogen bond and two pairs of unshared electrons that can “accept” a hydrogen bond
how many strong hydrogen bonds can water participate in?
two, one as acceptor and one as donor
why is water highly cohesive?
ability to form hydrogen bonds
what other properties does water have because of its cohesion?
high surface tension, why water remains a liquid at room temp, water less dense than other liquids, why ice floats
what are ionic interactions and how strong are they?
they are interactions between charged groups, intermediate in strength to covalent bonds and hydrogen bonds
how long are hydrogen bonds?
about 1.8 A
how long are covalent bonds?
1 A
what atoms are involved in hydrogen bonds?
N, O, or S attached to a H
what is a dipole-dipole interaction? how strong is it?
interaction between two strongly polar groups, weaker than hydrogen bonds
what are London dispersion forces? how strong are they?
occur between nonpolar molecules as a result of small fluctuations in their distribution of electrons that create a temporary separation of charge, molecules must be very close together; weakest interaction
what is a dielectric constant? is water’s high or low?
measure of a solvents ability to diminish the electrostatic attractions between dissolved ions; the higher the dielectric constant of the solvent, the less able the ions are to associate with each other; water has relatively high dielectric constant
what molecules are readily solubilized?
biological molecules that bear polar or ionic functional groups
what is a hydrophilic molecule
readily hydrated substances, “water-loving”
what is a hydrophobic molecule?
insoluble in water, “water-fearing”, lack polar groups
what happens when a hydrophobic substance is added to water?
does not dissolve, forms a separate phase
why is it thermodynamically unfavorable to dissolve a hydrophobic substance in water?
when a hydrophobic molecule is hydrated, it becomes surrounded by a layer of water molecules that cannot participate in normal hydrogen bonding with each other but instead must align themselves so that their polar ends are not oriented toward the nonpolar solute; constraint on structure of water represents a loss of entropy in the system
what happens when a large number of nonpolar molecules are introduced into a sample of water?
they do not disperse and become individually hydrated, but the nonpolar molecules clump together, removing themselves from contact with water, minimizes the amount of water molecules that cannot participate in hydrogen bonds because of the decreased surface area of exposed nonpolar molecules (minimizes loss of entropy)
what is the hydrophobic effect?
the exclusion of nonpolar substances from an aqueous solution
what are amphiphilic or amphipathic molecules?
have both hydrophobic and hydrophilic portions
what happens when amphipathic molecules are added to water?
polar groups of amphiphiles orient themselves toward the solvent molecules and are hydrated, while the nonpolar groups tend to aggregate due to the hydrophobic effect
what is a micelle?
a particle with a solvated surface and a hydrophobic core
what is a bilayer?
two-layered sheets, hydrophobic layer sandwhiched between hydrated polar surfaces, biological basis of membranes
what is a vesicle?
a structure formed when a lipid bilayer closes up to eliminate its solvent-exposed edges; many organelles have similar structure
what can pass through a lipid bilayer freely?
small nonpolar molecules such as O2
what cannot pass through a lipid bilayer freely?
polar and ionic solutes, large solutes
why can cells maintain their specific concentrations of ions, small molecules, and bipolymers even when the external concentration of these substances are quite different?
a barrier such as a bilayer can prevent the spontaneous diffusion of molecules down a concentration gradient
what are the products of water’s dissociation
a hydrogen ion or proton (H+) and a hydroxide ion (OH-); aqueous solutions do not actually contain lone protons, H+ can be visualized as combining with a water molecule to produce a hydronium ion (H3O+)
what is proton jumping?
a proton does not remain associated with a single water molecule, it appears to be relayed through a hydrogen-bonded network of water molecules; mobility of H+ in water is much greater than the mobility of other ions that must physically diffuse among water molecules (causes acid base reactions to be among the fastest)
what is the ionization constant of water?
Kw=10^(-14)=[H+ ][OH- ]
what is a neutral solution?
solution in which [H+]=[OH-]=10^-7, pH=7
what is an acidic solution?
solution in which [H+]>10^-7, pH<7
what is a basic solution?
solution in which [H+]<10^-7, pH>7
what is the equation for pH?
pH= -log[H+]
what does a difference of one pH unit mean?
a 10-fold difference in [H+]
what is an acid?
a substance that can donate a proton
what is a base?
a substance that can accept a proton
what does adding an acid to a solution do?
increases the concentration of [H+] and decreases the pH
what does adding a base to a solution do?
decreases the concentration of [H+] and increases the pH
what is the acid dissociation constant?
Ka= [H+][A-]/[HA]
what does a large Ka signify?
more likely the acid to ionize, more likely to donate a proton
pKa equation?
pKa = -log[Ka]
what does a small pKa indicate?
greater “strength” as an acid, more likely to ionize and donate a proton
what is a polyprotic acid?
a compound with more than one acidic hydrogen, has a pKa value for each dissociation, first proton dissociates with the lowest pKa value, subsequent protons less likely to dissociate and therefore have higher pKa values
Henderson-Hasselbalch equation?
pH = pKa + log [A-]/[HA]
what does it mean when pH=pKa?
the acid is half dissociated; exactly half of the molecules are in the protonated HA form and half are in the unprotonated A- form
what does it mean when pH is far below the pKa?
acid exists mostly in HA form
what does it mean when pH is far above the pKa?
acid exists mostly in the A- form
what constitutes a buffer system?
weak acid or base with it’s conjugate
why does the addition of a strong acid or base not cause a large change in pH of a buffer system?
when acid is added, some of the added protons combine with the conjugate base to reform the acid and therefore do not contribute to an increase in [H+]; when a strong base is added, some of the hydroxide ions accept protons from the acid to form water and do not contribute to a decrease in [H+]
what does the midpoint of a titration indicate?
exactly half of the protons have disocciated [HA]=[A-] and pH = pKa
what is the effective buffering capacity of an acid?
within on pH unit of its pKa
what is Le Chatelier’s principle?
a change in concentration of one reactant will shift te concentrations of other reactanct in order to restore equilibrium
how does the body regulate excess H+ ions?
H+ combines with HCO3- to reform H2CO3, which rapidly equilibrates with CO2 and H2O, some of CO2 given off as gas in the lungs
what is the body’s response to too few H+ ions?
breathing is adjusted so that less CO2 is lost during exhalation
how are long term pH adjustments made in the body?
the kidneys use a variety of mechanisms to excrete or retain H+, bicarbonate, and other ions; reabsorbs filtered HCO3- that is necessary to buffer the acids produced in metabolic processes before it is lost in urine, generate additional HCO3- to offset losses due to buffering of metabolic acids and exhalation of CO2; kidney cells produce CO2 which is converted to H+ and HCO3-, actively secrete H+, ammonium ion picks up a proton before being excreted, leaving an excess of HCO3-
what is acidosis?
blood pH less than 7.35
what is alkalosis
blood pH greater than 7.45
what causes metabolic acidosis?
accumulation of the acidic products of metabolism and can develop during shock, starvation, severe diarrhea (bicarbonate rich digestive fluid is lost), certain genetic diseases, and renal failure (damaged kidneys eliminate too little acid); common side effect is rapid deep breathing to “blow off” more acid in the form of CO2
what causes metabolic alkalosis?
results from prolonged vomiting, which represents a loss of HCl in gastric fluid, can be treated by infusing NaCl; also caused by overproduction of mineralalocorticoids which leads to abnormally high levels of H+ excretion and Na retention (does not respond to saline infusion); may experience apnea (cessation of breathing) or cyanosis (blue coloration) due to inadequate oxygen uptake, reflects body’s attempt to compensate for high blood pH by minimizing loss of CO2
respiratory acidosis
can result from impaired pulmonary function caused by blocked airway function, asthma, and emphysema; kidneys respond by adjusting their activity, increasing synthesis of enzymes that produce NH3, excretion of NH4+ helps correct the acidosis
respiratory alkalosis
caused by hyperventilation from fear/anxiety, exhaling too much CO2
