Ritalin is the trade name of a drug, methylphenidate, used to treat attention- deficit/hyperactivity disorder in young adults. The chemical structure of methylphenidate is (a) Is Ritalin an acid or a base? An electrolyte or a nonelectrolyte? (b) A tablet contains a \(10.0-\mathrm{mg}\) dose of Ritalin. Assuming all the drug ends up in the bloodstream, and the average man has a total blood volume of \(5.0 \mathrm{~L}\), calculate the initial molarity of Ritalin in a man's bloodstream. (c) Ritalin has a half-life of 3 hours in the blood, which means that after 3 hours the concentration in the blood has decreased by half of its initial value. For the man in part (b), what is the concentration of Ritalin in his blood after 6 hours?

Step by step solution

01

(a) Acid or base? Electrolyte or nonelectrolyte?

The structure of methylphenidate (Ritalin) is not given in the exercise, but it contains an amine group in its molecular structure. Amines can act as weak bases, so Ritalin is likely a weak base. It can form ions in solution by accepting a proton from water molecules, which means it is an electrolyte.

02

(b) Calculate the initial molarity of Ritalin in the bloodstream

To compute the initial molarity, we first need to convert the mass of Ritalin in a tablet (10.0 mg) to moles. Then, we'll divide the number of moles by the blood volume (5.0 L) to obtain the molarity. The molecular weight of Ritalin (methylphenidate) is approximately 233 g/mol. Converting the mass of Ritalin in a tablet to moles: \[10.0\ \text{mg} \times \frac{1\ \text{g}}{1000\ \text{mg}} \times \frac{1\ \text{mol}}{233\ \text{g}}\] Now we divide the moles of Ritalin by the blood volume to obtain the initial molarity: \[Initial\ Molarity = \frac{10.0 \times(1/1000) \times (1/233)}{5.0}\]

03

(c) Concentration of Ritalin in the blood after 6 hours

To find the concentration of Ritalin after six hours, we'll consider its half-life of three hours. This means that after three hours, the concentration is halved, and after another three hours, it's halved once again. So, after six hours, the concentration will be one-fourth (1/4) of its initial value. From part (b), we have the initial molarity: \[Initial\ Molarity = \frac{10.0 \times(1/1000) \times (1/233)}{5.0}\] After 6 hours, the concentration will be one-fourth of its initial value: \[Concentration\ after\ 6\ hours = \frac{1}{4} \times \frac{10.0 \times(1/1000) \times (1/233)}{5.0}\] Now we just need to perform the calculation to find the concentration of Ritalin in the blood after six hours.

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