Determine weight of drug from molarity and volume of the solution
4. Moles and Molarity 4.2) Molarity 4.2.1) Molarity - general
4.2.1.1) Molarity - general Normal 1
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How many grams of calcium chloride dihydrate (MW = 147 g/mol) should be dissolved in 300 mL of a solution so that the strength is 1 M?
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lb equals 44.1 g 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 300 mL, or 0.3 L.
[1] Using formula method:
`M=g/(aV) therefore g=MaV`
`g=1 × 147 × 0.3 = 44.1` grams. Ans.
[2] Using conceptual method:
First, count the number of moles (`n`) of calcium chloride dihydrate present in this solution. 1 M means, there is 1 number of moles of calcium chloride dihydrate present in 1000 mL of the solution.Therefore,
`(1\quad mol)/(1000 \quad mL)=x/(300 \quad mL) therefore x = 0.3 \quad mol`
Then, calculate how many grams of calcium chloride dihydrate will be contained in 0.3 mol. Mole (`n`) is the gram weight (`g`) divided by molecular weight (`a`), or `n=g/a`. Therefore, `g = n × a = 0.3 \quad mol × (147 \quad g/(mol)) = 44.1` g. Ans.