a buffer solution is needed to maintain a pH of 3.5 to 3.8 in a urine sample. Wh

Question

a buffer solution is needed to maintain a pH of 3.5 to 3.8 in a urine sample. Which of the following buffers would you use if 0.1 M Solutions of the weak acid and conjugate base are available? Why?
a. Formic acid/formate (Ka=1.8*10^-4)
b. carbonic acid/bicarbonate (Ka=4.3*10^-7)
c. ammonium/ammonia (Ka=5.6*10^-10)

3. A buffer solution to maintain a pH o135tn 38 in a urne sample which ot the following is needed acid and coniugare buffers would you use it o.1 M solutions of the weak base are available? Why? a. Formic acid/farmate lek, a 1.8 x 10 b. Carbonic acid bicarbonate K. 43 10n c, Ammonium/ammonia IK, -56 x 10

Explanation / Answer

To prepare a buffer first choose an acid with a pKa within a ±1 pH unit of the desired value.

In our case, lets see which has ph of this range

formic acid has a ka of 1.8 * 10-4

pKa = -log (ka) = -log (1.8 * 10-4) = 3.74

Carbonic acid has a ka of 4.3 * 10-7

pKa = -log (ka) = -log (4.3 * 10-7) = 3.746.37

Ammonium has a ka of 5.6 * 10-10

pKa = -log (ka) = -log (5.6 * 10-10) = 9.25

Thus Formic acid/ formate buffer can show a pH range of 2.74 to 4.74, thus can be manipulated to provide the desired pH range i.e. 3.5 to 3.8 needed in the experiment. Thus formic acid/ formate will be buffer solution used for this purpose

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