Caffeine (C₈H₁₀N₄O₂) is a stimulant found in coffee and tea. What is the mass percent of caffeine, %(m/m) , for a solution of caffeine dissolved in chloroform (CHCl₃) that has a concentration of 0.0890 m ?
Molar Mass(C₈H₁₀N₄O₂) = 194.19 g/mol

Question

Quizplus · Accepted Answer

To find the mass percent of caffeine in the solution, we need to first find the mass of caffeine present in the solution. We can use the given concentration and molar mass of caffeine to find this:

molarity = moles of solute / volume of solution
moles of solute = molarity x volume of solution

moles of caffeine = 0.0890 mol/L x 1.00 L = 0.0890 mol

mass of caffeine = moles of caffeine x molar mass of caffeine
mass of caffeine = 0.0890 mol x 194.19 g/mol = 17.8 g

Now, we can use the mass of caffeine and the total mass of the solution to calculate the mass percent:

mass percent = (mass of solute / mass of solution) x 100%
mass percent = (17.8 g / 105 g) x 100%
mass percent = 16.95%

Rounding to two significant figures gives us a mass percent of 1.7%, which corresponds to choice (B).

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