Problem: Caffeine (C8H10N4O2) is a stimulant found in coffee and tea. A solution of caffeine in the solvent chloroform (CHCl3) has a concentration of 0.0510 m.Calculate the percentage of caffeine by mass in the solution.

FREE Expert Solution

Molality of a solution is defined as the number of moles of solute per kilogram of solvent. It is represented as:


<math xmlns="http://www.w3.org/1998/Math/MathML"><menclose mathcolor="#0000FF" notation="box"><mi>m</mi><mo>&#xA0;</mo><mo>=</mo><mfrac><mrow><mo>&#xA0;</mo><mi>m</mi><mi>o</mi><mi>l</mi><mo>&#xA0;</mo><mi>s</mi><mi>o</mi><mi>l</mi><mi>u</mi><mi>t</mi><mi>e</mi></mrow><mrow><mi>k</mi><mi>g</mi><mo>&#xA0;</mo><mi>s</mi><mi>o</mi><mi>l</mi><mi>v</mi><mi>e</mi><mi>n</mi><mi>t</mi></mrow></mfrac></menclose></math>


We will solve this problem through these steps:

  • Find the molar mass of caffeine
  • Find the number of moles of caffeine and mass of chloroform using the molality of solution
  • Find the mass of caffeine
  • Find the mass percent of caffeine is solution


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Problem Details
Caffeine (C8H10N4O2) is a stimulant found in coffee and tea. A solution of caffeine in the solvent chloroform (CHCl3) has a concentration of 0.0510 m.

Caffeine consists of two fused rings with a six-membered ring with the points arranged vertically whose right side is shared by the lower left side of a five-membered ring. The six-membered ring has O as its upper left vertex and bottom point; all other vertices are C. The shared side is a double bond; the other sides are single bonds. The bottom point is single bonded to CH3; the lower left vertex is double bonded to O; the upper left vertex is single bonded to CH3; and the top point is double bonded to O. In addition to the shared side, the lower right side of the five membered ring is also a double bond; the other sides are single bonds. The point of the five member ring and the lower right vertex are N; the other vertices are C. The point is single bonded to CH3 and the upper right vertex is single bonded to H.

Calculate the percentage of caffeine by mass in the solution.

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What scientific concept do you need to know in order to solve this problem?

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Based on our data, we think this problem is relevant for Professor Raghavachari's class at IU.