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 M of penicillin V potassium solution. If the quantity of penicillin V potassium is 271.6 g, then determine the volume of the solution, in milliliter unit. The molecular weight of penicillin V potassium is 388 g/mol.
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lb equals 700 mL kg
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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.
[1] Using formula method:
`M=g/(aV) therefore V=g/(Ma)=(271.6 \quad g)/((1 (mol)/L) × (388 g/(mol)))`
`therefore V=0.7 \quad L` which is 700 mL. Ans.
[2] 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= (271.6 \quad g)/(388 \quad g/(mol)) = 0.7 \quad mol`.
Then, determination of the volume in which 0.7 mol of penicillin V potassium will be present to give a molarity of 1. From the definition of molarity, 1 M means, 1 mole of solute will be dissolved in 1L of solution. Therefore, we can write,
`(1 \quad mol)/(1 \quad L)=(0.7 \quad mol)/x therefore x = 0.7\quad L = 700\quad mL` Ans.