Question

Caffeine (C8H10N4O2) is a stimulant found in coffee and tea. A solution of caffeine in the solvent chloroform (CHCl3) has a concentration of 0.0490m.

a. Calculate the percentage of caffeine by mass in the solution.

b. Calculate the mole fraction of caffeine in the solution.

Answer 1

Solution :-

Concentration of the caffeine = 0.0490 m 0.0490 m means 0.0490 moles of caffeine in 1 kg solvent

Now lets calculate the mass of caffeine

Mass = moles * molar mass

          = 0.0490 mol * 194.19 g per mol

          = 9.515 g caffeine

Now lets calculate the mass of the solution

Mass of solution = mass of solvet + mass of solute

                              = 1000 g + 9.515 g

                              = 1009.515 g

a). % of caffeine = (mass of caffeine/ mass of solution )*100%

                        = (9.515/1009.515)*100%

                        = 0.942 %

b) mole fraction of the caffeine

moles of CHCl3 = 1000 g / 119.38 g per mol = 8.3766 mol

mole fraction of caffeine = moles of caffeine / (moles of caffeine + moles of CHCl3)

                                              = 0.0490 / (0.0490 + 8.3766)

                                             = 0.005816