CHEM 191 Lecture 7and8 Flashcards
what is a buffer solution
a solution of weak acid and its conjugate base, both at reasonable concentration, which will maintain a reasonably constant pH on addition of significant amounts of H3O+ and OH- ions. the pH of a buffer solution is also unaffected by reasonable dilution of the solution
in a buffer solution is the weak acid/base reacting with water or a strong acid/base
a strong acid/base (H3O+ OR OH-)
can the equation pH = pKa + log([A-]/[HA]) be used in simple acid/base problems
no
what is the relationship between pH and pKa when the concentration of the conjugate acid and base in a buffer are equal
pH = pKa - because it is equally as effective at neutralising added base as it is added acid
do you have to mix together an acid and its conjugate base to make a buffer solution
no - for example, you can add NaOH and CH3COOH together to make a buffer because NaOH completely dissociates
if a weak acid reacts with a strong base will the reaction go to completion
yes
what do we mean when we say the buffer capacity has been exhausted
this is the point where either the weak acid or its conjugate base is completely used up and the pH will change significantly
what is always the essential reaction of an acid base titration
neutralisation
what is the half equivalence point
the point where pH = pKa - the concentrations of the acid/base and its conjugate are equal
what is the equivalence point
the point where the reaction has gone to completion and the stoichiometry is satisfied because we have the same number of moles of acid as we do base
why is the pH not always 7 at the equivalence point
this is due to the reaction of the conjugate base/acid with water to give OH- or H3O+
what is the alkaline region
the region in which pH is solely determined by the amount of excess OH- ions added to the solution after the equivalence point has been reached
for strong acid/base reactions what is the pH at the equivalence point
7
why don’t strong acid base reasons have a buffer zone
because the pH is affected by reasonable dilution
do diuretic acids donate their protons at the same time
no they donate their protons one at a time
are amino acids chiral molecules
yes - except one that has just a H as its R group - they are also all in their left handed form
what is a zwitterion
a molecule that has both a positive and negative charge, but the overall the molecule is neutral - they are sometimes called internal salts
what is the cationic form of an amino acid
under very acidic conditions both the COOH and NH3+ groups will be protonated
what is the anionic form of an amino acid
under very basic conditions, both the COO- and the NH2 groups will be deprotonated. the carboxylic acid always loses its proton first
why are diprotic acids more acidic than normal weak acids
because it is easier to lose a proton from a positively charged ion than from a neutral molecule
what is pI
the isoelectric point is the point where most of the molecules have no charge - it occurs when one mole equivalent of OH- has been added
what is the pKa (and therefore the pH) when 0.5 equivalents OH- has been added to an acid base titration
2.35
what is the pKa (and therefore pH) when 1.5 equivalents oh OH- have been added to an acid base titration
9.78
when is the titration complete
when 2 equivalents of OH- have been added
