[sasuke07]

Hi, so were doing our first organic chem. Lab tomorrow and i literally have no idea how to do 3 of the problems. please help.
1. Caffeine occurs naturally in tea leaves and coffee beans. Pure caffeine (mp 238°C) is a white
crystalline solid material at room temperature. It is classified as an alkaloid – a nitrogen containing
basic compound that is obtained from plants and has physiological effects in the body. A student
pulverizes 10.06 grams of coffee beans into a finely ground powder by using a mortar and pestle.
The caffeine is then extracted into 250 mL of boiling dichloromethane (CH2Cl2) by the same solidliquid extraction technique used in Unit 1. After 30 minutes, the solution is filtered hot to remove a
large amount of brown insoluble material. Dichloromethane is removed from the filtrate via distillation,
leaving 0.14 grams of caffeine behind, as a white solid. Determine the percentage of isolated caffeine
with respect to the starting amount of crude coffee beans.
2a. The Gabriel synthesis is a two-step preparation of primary amines, with the alkylation of potassium phthalimide
constituting the first step.
What is the theoretical yield of compound B, in grams, when
142.9 g of compound A are allowed to react with 98.1 g of
potassium phthalimide?
2b. Given that 138.7 g of B were obtained what is the
percentage yield of compound B?
3. Usnic acid occurs naturally in a variety of lichens and has antibiotic
properties. Pure usnic acid (mp 202-203°C) is a yellow crystalline solid material at
room temperature. A student crushes 21.0 grams of lichen into a finely ground
powder by using a mortar and pestle. The usnic acid is then extracted into 100 mL
of boiling acetone by the same solid-liquid extraction technique used in Unit 1.
After 30 minutes, the solution is filtered hot to remove a large amount of insoluble
material. Acetone is removed from the filtrate via distillation, leaving 0.46 grams of
a yellow solid (mp 191-197°C). Comment on the composition of this yellow solid in
terms of the number of component(s) present.

Instead of giving me the answers could some point out ways to solve these 3 problems because i have
no idea. Thanks.

[sjb]

Hi, so were doing our first organic chem. Lab tomorrow and i literally have no idea how to do 3 of the problems. please help.
1. Caffeine occurs naturally in tea leaves and coffee beans. Pure caffeine (mp 238°C) is a white
crystalline solid material at room temperature. It is classified as an alkaloid – a nitrogen containing
basic compound that is obtained from plants and has physiological effects in the body. A student
pulverizes 10.06 grams of coffee beans into a finely ground powder by using a mortar and pestle.
The caffeine is then extracted into 250 mL of boiling dichloromethane (CH2Cl2) by the same solidliquid extraction technique used in Unit 1. After 30 minutes, the solution is filtered hot to remove a
large amount of brown insoluble material. Dichloromethane is removed from the filtrate via distillation,
leaving 0.14 grams of caffeine behind, as a white solid. Determine the percentage of isolated caffeine
with respect to the starting amount of crude coffee beans.

You have 10.06 g of coffee powder, which yields 0.14 g of caffeine. What percentage is that?

2a. The Gabriel synthesis is a two-step preparation of primary amines, with the alkylation of potassium phthalimide
constituting the first step.
What is the theoretical yield of compound B, in grams, when
142.9 g of compound A are allowed to react with 98.1 g of
potassium phthalimide?
2b. Given that 138.7 g of B were obtained what is the
percentage yield of compound B?

2a. What's the balanced reaction for the reaction? What are compounds A and B

2b. Similar to 1

3. Usnic acid occurs naturally in a variety of lichens and has antibiotic
properties. Pure usnic acid (mp 202-203°C) is a yellow crystalline solid material at
room temperature. A student crushes 21.0 grams of lichen into a finely ground
powder by using a mortar and pestle. The usnic acid is then extracted into 100 mL
of boiling acetone by the same solid-liquid extraction technique used in Unit 1.
After 30 minutes, the solution is filtered hot to remove a large amount of insoluble
material. Acetone is removed from the filtrate via distillation, leaving 0.46 grams of
a yellow solid (mp 191-197°C). Comment on the composition of this yellow solid in
terms of the number of component(s) present.

What does a broad melting point suggest?

[sasuke07]

THanks for the help.
1. For one i got 1.39% can  anyone tell me if its correct. I just did .14/10.06 to get the percentage.
2. as for the balanced equation its the image attached. It doesn't say how many many moles it takes of each and
it also does not say what compound A and B is.
3. Wouldn't a broad melting point mean the substance under experiment would contain more impurities, making it less pure. (now my question would be would this work as an answer. when it was asking about composition)

[sjb]

THanks for the help.
1. For one i got 1.39% can  anyone tell me if its correct. I just did .14/10.06 to get the percentage
...
3. Wouldn't a broad melting point mean the substance under experiment would contain more impurities, making it less pure. (now my question would be would this work as an answer. when it was asking about composition)

Sounds good, I can't imagine that you actually have to say that there are now 34 (or 2, or 5, or n) different compounds just based on a melting point. Minor point, but have you checked significant figures?

2. as for the balanced equation its the image attached. It doesn't say how many many moles it takes of each and
it also does not say what compound A and B is.

OK, let's look at the structures. Can you see any key features in A that also appear in B. What ratio do they appear in?

[sasuke07]

It looks like The 2 rings with N from Structure A makes it into B, So would that make it a 1:1 structure.

[sjb]

It looks like The 2 rings with N from Structure A makes it into B, So would that make it a 1:1 structure.

OK, so how many moles of A and potassium phthalimide were used? To form how many moles of B?