2.When the patient was brought to the emergency room, you had suspected that some aspirin remained...

2.When the patient was brought to the emergency room, you had suspected that some aspirin remained undissolved and this was confirmed when she was experiencing severe alkylosis 8-10 hours later. You used a gastric lavage at pH=8.5 to effectively remove any undissolved aspirin. This treatment solubilizes the aspirin so that it can easily be removed from the stomach.

a. Calculate the percentage of protonated and unprotonated forms of salicylic acid at the pH of the stomach, which is usually around 2.0

b. Calculate the percentage of protonated and unprotonated forms of salicylic acid at the pH of the gastric lavage (pH=8.5). Why does the gastric lavage result in increased solubility of the drug? (Note: Assume that the pKa values of the carboxylate group in salicylic acid and acetylsalicylic acid are the same; pKa=3.0)

3. a. Use the Henderson-Hasselbach equation to determine the ratio of HCO3- to H2CO3 in the patient’s blood 10 hours after aspirin ingestion.

b. How does this compare to the ratio of HCO3- to H2CO3 in normal blood (indicate value used from the range given in the table). (pKa1=6.35).

c. Can the H2CO3/HCO3- system serve as an effective buffer in this patient? Explain

Solutions

Expert Solution

2.a) The pKa of salicylic acid is 3.0

Using the Henderson Hasselbach equation

pH = pKa + log(unprotonated s/protonated ) we can calculate the percentage of protonated and unprotonated forms of salicylic acid at the pH = 2

pKa - pH = - log [unprotonated]/[protonated]

3.0 – 2.0 = - log [unprotonated]/[protonated] = 1

[Unprotonated]/[protonated] = 10^(-1) = 0.1

[Unprotonated] +[protonated] = 0.1 + 1.0 = 1.1

Percentage of unprotonated forms of salicylic acid at pH2 = (0.1 / 1.1) x 100 = 9.10%

Percentage of protonated forms of salicylic acid at pH2 = (1.0 / 1.1) x 100 = 90.90%

pKa - pH = - log [unprotonated]/[protonated]

3.0 – 8.5 = - log [unprotonated]/[protonated] = -5.5

[Unprotonated]/[protonated] = 10^(5.5) = 316227.766

[Unprotonated] +[protonated] = 316227.766 + 1.0 = 316228.766

Percentage of unprotonated forms of salicylic acid at pH 8.5 = (316227.766/316228.766) x 100

= 99.9996%

Percentage of protonated forms of salicylic acid at pH 8.5 = (1/316228.766) x 100

= 0.0004%

The gastric lavage results in increased solubility of the drug. All the salicylic acid is converted to soluble salicylate (99.9996) only trace amounts of salicylic acid (0.0004%) remain in the stomach

queen_honey_blossom answered 1 year ago

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