Soal IChO Ke-26

THEORETICAL PROBLEM No 1

(9 blue points, 8 red points)

Lactic acid is formed in the muscles during intense activity (anaerobic metabolism). In the blood, lactic acid is neutralized by reaction with hydrogen carbonate. This will be illustrated by the following calculations:

Lactic acid written HL is monoprotic, and the acid dissociation constant is K(HL) = 1.4^.10^-4.

The acid dissociation constants for carbonic acid are: K(a1) = 4.5^.10^-7 and K(a2) = 4.7^.10^-11.

All carbon dioxide remains dissolved during the reactions.

a) Calculate pH in a 3.00^.10^-3 M solution of HL.

b) Calculate the value of the equilibrium constant for the reaction between lactic acid and hydrogen carbonate.

c) 3.00^.10^-3 mol lactic acid (HL) is added to 1.00 L of 0.024 M solution of NaHCO₃(no change in volume, HL completely neutralized).

i) Calculate the value of pH in the solution of NaHCO₃ before HL is added.

ii) Calculate the value of pH in the solution after the addition of HL.

d) pH in the blood of a person changed from 7.40 to 7.00 due to lactic acid formed during physical activity. Let an aqueous solution having pH = 7.40 and [HCO₃^-] = 0.022 M represent blood in the following calculation. How many moles of lactic acid have been added to 1.00 L of this solution when its pH has become 7.00?

e) In a saturated aqueous solution of CaCO₃(s) pH is measured to 9.95. Calculate the solubility of calcium carbonate in water and show that the calculated value for the solubility product constant K_sp is 5^.10^-9.

f) Blood contains calcium. Determine the maximum concentration of “free” calcium ions in the solution (pH = 7.40, [HCO₃^-] = 0.022 M) given in d).

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