Prepare an ice bath in a 100-mL beaker on a magnetic stir plate. To a clean, dry
ID: 532433 • Letter: P
Question
Prepare an ice bath in a 100-mL beaker on a magnetic stir plate. To a clean, dry 5.ml conical vial, pipet mL of methyl To the methyl benzoate, add 0.45 ml of concentrated (18 M) sulfuric acid and a spin vane Attach an air condenser to the coni cal vial. Carefully clamp the apparatus so that the vial is immersed in the ice bath Begin stirring. Into a clean, dry 3-mL conical vial, add 0.15 mL of concentrated (18 M) sulfuric acid and 0.15 mLof concentrated (16 M) nitric acid. Cool the mixture in a sec ond ice bath. With a Pasteur pipet, slowly add the cooled sulfuric acid-nitric acid solu tion to the stirred solution of methyl benzoate through the air condenser. The addition should take approximately 15 minutes. Adding the nitrating agent more rapidly increases the amount of by-products and decreases the yield. Con When all the nitrating agent has been added, carefully remove the ice bat tinue stirring until the reaction has come to room temperature. Then let the reaction flask stand undisturbed for 15 minutes. Place ice in a 30-mL beaker. With a Pas. l mL teur pipet, transfer the reaction mixture to the beaker Rinse the reaction vial with Hirsch of cold water. When the ice has melted, vacuum filter the crude crystals using a funnel. Wash the crystals with two 1.0 ml portions of cold water and finally with two 0.3-mL portions of cold methanol. The crude product can be recrystallized from methanol. Record the mass of the dry product and calculate the yieldExplanation / Answer
In first addition,
Number of molesof H2SO4 = concentration of H2SO4 X volume of H2SO4
= 18 mol L-1 X 0.45 X 10-3 L
= 8.1 X 10-3 mol
= 8.1 mmol
NB: 1 M = 1 mol L-1
In second addition,
Number of molesof H2SO4 = concentration of H2SO4 X volume of H2SO4
= 18 mol L-1 X 0.15 X 10-3 L
= 2.7 X 10-3 mol
= 2.7 mmol
Total number of molesof H2SO4 = 8.1 + 2.7 = 10.8 mmol
Number of molesof HNO3 = concentration of HNO3 X volume of HNO3
= 16 mol L-1 X 0.15 X 10-3 L
= 2.4 X 10-3 mol
= 2.4 mmol
Number of moles of methyl benzoate = mass of methyl benzoate / Molar mass of methyl benzoate
= Density of methyl benzoate X Volume of methyl benzoate / Molar mass of methyl benzoate
= 1080 g L-1 X 0.2 X 10-3 L / 136.15 g mol-1
= 1.6 X 10-3 mol
= 1.6 mmol