### 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 magnesium acetate tetrahydrate (MW = 142.4 g/mol) should be dissolved in 1000 mL of a solution so that the strength is 0.65 M?

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lb equals 92.56 g 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 1000 mL, or 1 L.

[1] Using formula method:
M=g/(aV) therefore g=MaV
g=0.65 × 142.4 × 1 = 92.56 grams. Ans.

[2] Using conceptual method:
First, count the number of moles (n) of magnesium acetate tetrahydrate present in this solution. 0.65 M means, there is 0.65 number of moles of magnesium acetate tetrahydrate present in 1000 mL of the solution.Therefore,
(0.65\quad mol)/(1000 \quad mL)=x/(1000 \quad mL) therefore x = 0.65 \quad mol
Then, calculate how many grams of magnesium acetate tetrahydrate will be contained in 0.65 mol. Mole (n) is the gram weight (g) divided by molecular weight (a), or n=g/a. Therefore, g = n × a = 0.65 \quad mol × (142.4 \quad g/(mol)) = 92.56 g. Ans.

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