Lecture 2 Flashcards
In a weak acid equilibrium, describe what the “weak acid” and “conjugate base” serve as. Also describe what the dissociation constant tells you about a particular weak acid equilibrium.
The weak acid (HA) serves as the proton donor
The conjugate base (A-) serves as the proton acceptor
The dissociation constant (Ka) describes how easily the weak acid will dissociate into the conjugate base and H+ ions
In a weak base equilibrium, describe what the “weak base” and “conjugate acid” serve as. Also describe what the dissociation constant tells you about a particular weak base equilibrium.
The weak base (B) serves as the proton acceptor
The conjugate acid (BH+) serves as the proton donor
The dissociation constant (Ka) describes how easily the weak base will accept protons from water
(still called the dissociation constant for bases even though acids are what actually dissociates, and bases do not)
Compare the Ka, pKa, and energy of interaction between strong and weak acids
Ka: Larger in strong acids
pKa: smaller in strong acids (opposite of Ka value)
Energy of Interaction: smaller in Strong acids (it takes less energy input to make strong acids dissociate compared to weak acids)
Compare the Ka, pKa, and energy of interaction between strong and weak bases
Ka: Larger in strong bases
pKa: smaller in strong bases (opposite of Ka value)
Energy of Interaction: larger in Strong bases (larger means more negative, and the more negative the energy of interaction is for a base, the more likely water is to give the base a proton)
Describe why the pH scale is 0 to 14
This is bc the equilibrium constant of water is 10^-14 M
What is the physiological pH of the human body?
7.4
Define the term Buffer (give both examples of a buffer)
Buffers are weak acids or bases that can stabilize pH
Describe what it means in terms of the protonation/deprotonation of the molecules of a solution when the following conditions occur
pH < pKa
pH > pKa
pH = pKa
pH < pKa: most of the molecules are protonated (since the [HA] > [A-])
pH > pKa: most of the molecules are deprotonated (since the [HA] < [A-])
pH = pKa: the molecules are just as likely to be protonated as they are to be deprotonated
Define Isoelectric point
the pH where all of the molecules of a given species in solution have an OVERALL charge of 0
Describe what it means in terms of the charge of a molecule when the following conditions occur
pH < pI
pH > pI
pH = pI
pH < pI: the molecule has a positive charge
pH > pI: the molecule has a negative charge
pH = pI: the molecule has no net charge
What do you need to use in order to find the isoelectric point of a molecule?
the +1 and -1 pKa’s
(any pKa values beyond these is meaningless to the calculation of the isoelectric point bc we want to find when the species has a net charge of zero)
explain what isoelectric focusing is and how it works
isoelectric focusing is a form of electrophoresis where you establish a pH gradient into the gel, and then add proteins and supply charge
the proteins will migrate the to pH that represents their pI (isoelectric point) bc they will have no charge there and therefor will not migrate due to the current running through the gel
beginning with pH > pI of a protein, then moving to pH = pI, and finally pH < pI, explain the levels of protein solubility will occur throughout this range and why
at pH > pI: at high pH, proteins are deprotonated and VERY soluble because of their negative charges repelling one another
at pH = pI: at it’s isoelectric point pH, protein aggregates because it has no net charge, which allows the + and - regions of the molecule to interact with one another
at pH < pI: at low pH proteins are protonated and soluble because of repulsions due to their positive charge
State the first law of thermodynamics
Energy is neither created or destroyed in a closed system
everything will always have some kinetic (motion, performing work) and potential energy (chemical energy is potential energy in chemical bonds)
True or False:
a cell can gain or lose energy and it will not violate the first law of thermodynamics. explain.
True
a cell is not a closed system, so its all good
