### 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 NaBr (MW = 102.9 g/mol) should be dissolved in 550 mL of a solution so that the strength is 1.6 M? Click on the button below to see the answer and explanations

lb equals 90.552 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 550 mL, or 0.55 L.

 Using formula method:
M=g/(aV) therefore g=MaV
g=1.6 × 102.9 × 0.55 = 90.552 grams. Ans.

 Using conceptual method:
First, count the number of moles (n) of NaBr present in this solution. 1.6 M means, there is 1.6 number of moles of NaBr present in 1000 mL of the solution.Therefore,
(1.6\quad mol)/(1000 \quad mL)=x/(550 \quad mL) therefore x = 0.88 \quad mol
Then, calculate how many grams of NaBr will be contained in 0.88 mol. Mole (n) is the gram weight (g) divided by molecular weight (a), or n=g/a. Therefore, g = n × a = 0.88 \quad mol × (102.9 \quad g/(mol)) = 90.552 g. Ans.