Please help!!! General Chemistry Workshop 4: Buffers A buffer is a solution comp
ID: 487131 • Letter: P
Question
Please help!!! General Chemistry Workshop 4: Buffers A buffer is a solution comprised of a weak acid and its conjugate weak base or a weak base and its conjugate weak acid. The pH of a buffer can be calculated using the Henderson-Hasselbach equation: PH pK.+ log (IBasel/IAcid]. The pH of a buffer is largely dictated by the plk, ofthe the buffer. A buffer that contains more base than acid will have a pH above its pK. value and a buffer that contains more acid than base will have a pH below its pKa value. Buffers are very important because they resist changes in pH upon the addition of acidic or basic solutions. One of the most important buffers for human life is the bicarbonate buffer that maintains our blood pH levels at 74, One of the components of this buffer is the polyprotic carbonic acid (Hacos). 1. Let's take a moment to consider the bicarbonate buffer. a) Write the 2 equilibrium reactions for 2 steps of the aqueous dissociation of Hacos. Hao. b) Use the chem appendix on Sapling to find the K values for Hacon. Now calculate the corresponding pK values and write BOTH next to the appropriate equilibrium reactions in part 1(a). c) If you wanted to go into the lab and emulate the buffer solution that exists in your blood which combination of compounds would you mix together to create your buffer? Haco and KHCOs KHCOh and Kaco's Haco and xacos EXPLAIN your choice: d) Which of the following when mixed together would result in the formation of a buffer n each case. solution? Explain your answers 40 ml of 0.1 M KHC0 150 mL of 0.1 M KOH 20 ml of 0.2 M C0,2 100 mL of 0.1 M 20 mL of 0.1 M HClExplanation / Answer
Buffers
Part 1.
1. For bicarbonate buffer in blood at pH 7.4
a) dissociation of H2CO3
H2CO3 + H2O <==> HCO3- + H3O+ Ka1 = [HCO3-][H3O+]/[H2CO3] pKa1 = -log[Ka1]
HCO3- + H2O <==> CO3^2- + H3O+ Ka2 = [CO3^2-][H3O+]/[HCO3-] pKa2 = -log[Ka2]
b) Ka1 = 4.2 x 10^-7 ; pKa1 = 6.35
Ka2 = 4.8 x 10^-11 ; pKa2 = 10.33
c) For the buffer in blood we would use,
H2CO3 and HCO3-
combination
The best combination would be the one whose pKa value is closest to the desired pH, which is pKa1 in this case.
d) Buffer solutions
40 ml of 0.1 M KHCO3 150 ml of 0.1 M H2CO3
20 ml of 0.1 M CO3^2- Yes No
100 ml of 0.1 M H2CO3 Yes No
20 ml of 0.1 M HCl Yes No
A buffer is a combination of weak acid with its syrong conjugate base or weak base in combination with its strong conjugate acid.
Part 2.
a) pH of the given buffer would be above pH 7 as the ratio of KOCl to HOCl is below 1.
b) pH of the buffer = 7.45 + log(0.08/0.12) = 7.28
c) If 2.5 ml of 10 M KOH was added
the pH of the buffer would,
increase
base would react with HOCl to produce more KOCl
d) pH = 7.45 + log(0.08 x 0.5 + 10 x 0.0025)/(0.12 x 0.5 - 10 x 0.0025)
= 7.72