Ch.12 - SolutionsWorksheetSee all chapters
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Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Solution:
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.

Solution: 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 th

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.

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.

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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