14B.2 Flashcards
what is a buffer solution
a solution that minimizes the change in pH when small amounts of either acid or base
what are the two ways to make buffer solutions
- add a weak base and its conjugate acid
- add a weak acid and its conjugate base
what is an example of weak acid and its conjugate base
ethanoic acid and sodium ethanoate
the salt of a weak acid has to be
soluble in water
weak acid and its conjugate base forms a pH of
less than 7
in buffer solution pH calculations saying that the extend of acid dissociation is negligible tells us that
- the acid concentration at eq will be half the starting concentration
- the bass of the acid will be considered to be made up from the acid salt so at eq it will have half the starting concentration (same as the acid)
why do we use half the concentration of the acid and the salt in Buffer solution pH calculations
because equal volumes of each solutions were mixed, so the total volume of the mixture is twice the volume of each
when adding a little base to a buffer solution what will happen
the Oh ions would react with the acid to form a base and H2O
when adding a little acid to a buffer solution what will happen
H ions would react with the base to form a weak acid
why is there a minimal effect on pH when adding small amounts of acid and base in buffer solutions
because the extent of acid dissociation is ignored we will have a large amounts of acid, and because the full dissociation of the salt we would have large amount of the conjugate base, therefore any addition of small amounts of acid and base will barely effect the acid and its base since they have large values of concentration so the effects are negligible. so the equation of [H] ions is given by Ka x acid/base so the Ka remains constant at a set temp, and the ratio of acid/base also remains fairly constant since they come at large values making the acid/base ratio fairly constant so the value of the [H] remains constant
when adding a 0.01 mol of H+ ions what will happen to the concentration of acid and its conjugate base
since the H ions would react with the base to form the acid and its a 1:1 ratio the new con of the acid would be 0.01 increase, and the con of the base would be 0.01 decrease
the concentration of a base would be the same as its salt if
sodium or potassium salt is used
what is the Henderson-Hasselbalch equation
pH = pKa + salt or base/acid (derivation page 97)
what is an example of weak base and its conjugate acid buffer solution
ammonia and ammonium ion which is usually supplied in the form of ammonium chloride
what is the pH of a buffer solution made from weak base and its conjugate acid
greater then 7
what is the buffer action for weak base and its conjugate acid
the dissociation of the acid provides large amounts of the acid and the base so with relatively large amounts of base acid and the base there change when adding a [H] OR [OH] ions would negligible so pH = pKa + base/acid with pKa being constant at a set temp and the base/acid ratio being fairly constant the pH would remain constant
how to make buffer solutions
page 98
what is the Ka of ethanoic acid dissociation
1.74 x 10^-5
what is the Ka of ammonium dissociation
5.62 x 10^-10
why are buffer solutions important in our bodies
because enzymes work best in certain conditions and having buffer solutions provide small changes of pH keeping thoose conditions
what is the most important buffer solution in the body
carbonic acid and its conjugate base which is hydrogen carbonate
why is the carbonic acid and hydrogen carbonate the most important buffer in the body
it is coupled with the respiratory system of the body
how does the body maintain its pH in the carbonic acid and hydrogen carbonate buffer solution
for loss of H - sometimes when people diuretics the body excretes large amounts of urine that can contain acid, so when acid is lost the eq shifts to the right making more carbonic acid ionize to form H+ returning the pH to normal
for gain of H - when the body gains acid maybe through lactic acid the eq would shift to the left forming more carbonic acid which would then breakdown into CO2 which will be removed more the body through breathing restoring the the pH back to its original value
what is the problem with carbonic acid
it unstable and can break down to from CO2(aq) and H2O(aq)
