### Determine volume of the solution from molarity and weight of drug

4. Moles and Molarity 4.2) Molarity 4.2.1) Molarity - general

4.2.1.1) Molarity - general Normal 1

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A pharmacists needs to prepare 1.55 M of penicillin V potassium solution. If the quantity of penicillin V potassium is 270.63 g, then determine the volume of the solution, in milliliter unit. The molecular weight of penicillin V potassium is 388 g/mol. Click on the button below to see the answer and explanations

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lb equals 450 mL kg

Molarity is the number of moles (n) dissolved per liter of solution (V). Again, mole is the weight in gram (g) divided by the molecular weight (a).
In this example, the volume of the solution is to be found out.

 Using formula method:
M=g/(aV) therefore V=g/(Ma)=(270.63 \quad g)/((1.55 (mol)/L) × (388 g/(mol)))
therefore V=0.45 \quad L which is 450 mL. Ans.

 Using conceptual method:
First, count the number of moles (n) of penicillin V potassium present in this solution. Mole is the gram amount of the solute divided by molecular weight. Therefore, n= (270.63 \quad g)/(388 \quad g/(mol)) = 0.6975 \quad mol.
Then, determination of the volume in which 0.6975 mol of penicillin V potassium will be present to give a molarity of 1.55. From the definition of molarity, 1.55 M means, 1.55 mole of solute will be dissolved in 1L of solution. Therefore, we can write,
(1.55 \quad mol)/(1 \quad L)=(0.6975 \quad mol)/x therefore x = 0.45\quad L = 450\quad mL Ans.

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