Weak Acids and Bases Flashcards
Conjugate acids and bases
Weak acids and bases partially dissociate in aqueous solution and there is an equilibrium between protonated and deprotonated forms. Protonated, can donate an H+ to solution (conjugate acid). The deprotonated form (can bind to H+ and lower the h+ in solution) is conjugate base.
a in Ka
acid dissociation
equilibrium constant
ratio of products divided by reactnats
large Ka
strong net dissociation producing lots of H+ and a large numerator
strong acids
small Ka
weak net dissociation
Which way will a reaction lie?
lies further to the right (more dissociation)
Anion exchange chromatography
Laboratory procedure for separating molecules having different net negative charges.
Column contains functional groups which are positive and binds negative anions. A mixture of biological anions are loaded on top of column where they are bound by positively charged resin. The column rinsed with NaCl solution. The Cl- starts binding to column competing with the biological anions for the positive sites on resin. The Cl- anion and biological anion EXCHANGE positions. Cl- sticks to the column and biological molecules re enters the solution. The most weakly bound biological anion, having the smallest net negative charge will be completed with dilute Cl- and will exit first from column. The most strongly bound biological anion having the largest negative charge will require high competing Cl- to loosen up from column. THE MOST NEGATIVE CHARGED BIOLOGICAL ANION ELUTES LAST.
Three ionized atoms
N+, O- and S-
Positive N has four electrons
Neutral O or S has 6 electrons but with a negative has seven electrons
Henderson Hasselbach relationship
pKa=log(protonated/deportonated) + pH
when pKa=pH, 0=log(protonated/deprotonated) which means protonated/deprotonated equals to one. The midpoint of this curve where 50% of each form will be is pH=pKa.
Use of Henderson Hasselbach
when solution at low pH (lower than pKa) then pKa-pH is a positive quantity and numerator>denominator.
What is an equivalent
One equivalent of NaOH is the amount of NaOH that is needed to completely titrate one functional group on the organic molecule (to cause one H+ ion to dissociate).
Buffers
a solution containing a mixture of protonated and deprotonated forms of a weak acid or base
good buffering means a large change in amount of strong base/acid added (delta X) accompanied by small change in pH (delta y)
small slope (delta y/deltax) good buffer: having almsot horizontal line and maintain reactions at a relatively constant pH
half the buffer in the protonated (CH3-COOH) form is capable of neutralizing incoming OH- and half is in the deprotonated (CH3-COO-) form capable of neutralizing incoming H+
Titration curve of glycine
low pH form at the extreme left side is fully protonated form. The fully protonated forms of amino and carboxyl groups are NH3+ and COOH so net charge is +1 at low pH.
Deprotonated form includes neutral NH2 and deprotonated COO- net charge -1 at high pH.
Isoelectric point pI of glycine
pH where net charge on molecule is zero (positive charges equal negative charges)
structure in the middle is COO- NH3+
CO2 effect on pH of blood
When CO2 dissolves in water, it combines with H2O to form carbonic acid (h2co3) which dissociates into bicarbonate (hco3-) and H+. Any process that adds/removes CO2 to system causes a shift in equilibrium.
Effect of CO2 in lungs
CO2 is exhaled into atmosphere. Depletion of CO2 causes the reaction to shift towards repelenishing loss of CO2 and lowers the amount of acid, increasing the pH slightly. (7.4)
Effect of CO2 in muscles
in muscles, metabolism converts glucose (c6h12o6) into co2 and h20. Excess co2 is added to the blood in muscles. Adding co2 to the right of the diagram causes a shift in the series of reaction towards the other end. Increasing CO2 will be to increase H+ lowering pH of blood in muscles.
Hemoglobin CO2
Changes in pH influence the hcarge on a titratable NH+ group in hemoglobin. That group has pKa of 7 and turning the psotiive charge of this group on and off affects its attraction to a negative COO- nearby in the protein and causes structural changes which affect the ability of hemoglobin to bind oxygen.
Structures of AMP, ADP, ATP
AMP: adenosine mono phosphate
ADP: adenosine di phosphate
ATP: adenosine tri phosphate
Different phosphorylates forms of adenosine
Ion exchange purification of adenosine derivatives
Neutral adenosine eluts first after a low salt buffer has been used to rinse the column. Highly negative ATP ELUTES last when nigh salt buffer is passed through.
Order of elution of adenosine AMP ADP ATP is in the order of their net negative charge because the more negative molecules bind more tightly to the positive column and require higher concentrations of negative Cl- to compete with them for the positive sites on column
