Question

QUESTION: WILL AWARD MEDAL AND FAN

Answer 1

Assuming that the density of the coffee is 1.00 g/mL, calculate the concentration of the caffeine expressed in % (m/m). Reminder: m/m means mass/mass; in other words, this percent is based on the mass of the caffeine and the mass of the beverage rather than the volume of the beverage

Answer 2

did they give you any other information in this question?

Answer 3

No

Answer 4

this is clearly part of another problem there has to be more information

Answer 5

Well a cup of coffee has 95mg of caffeine 1 cup = 237 grams of caffeine, was this part of a lab experiment?

@Ac3 I agree

Answer 6

I can take a picture

Answer 7

Yes it was part of a lab experiment. We used 75 mL of coffee

Answer 8

\[\frac{ 1 gram }{ mL } = \frac{ 75grams }{ 75mL } \]

so we would have 75 grams of coffee

Answer 9

There's something else we need though, can you post a picture of what you have?

Answer 10

did you see how i was able to get that right? the density was 1 gram per mL and we had 75 mL of coffee so we must have 75 grams of coffee.

Answer 11

I understood :)

Answer 12

Okay, the question is asking for a percentage of caffeine, so we need to know some kind of mass or something

Answer 13

this seems to be more like a pre-lab question am i right? if not what is your data from this experiment?

Answer 14

I got 194.194 grams but it doesn't seem right

Answer 15

can you take a picture of what you did and post it

Answer 16

You need to work with the numbers you got from the lab, and then explain why you may have arrived at the correct/incorrect answer in your discussion.

Answer 17

i see @cimberjackson you performed an extraction and filtered caffeine out from the original mixture.

To me this question is asking for the percentage of caffene in mass.

so you need the original starting volume of your caffeine.

then you can use the density 1g/mL to convert it to grams. because you can easily find out how many grams you have for caffeine.

Answer 18

FYI you can easily determine how good your recrystaliation/purification was by determining the melting point of caffeine. if your sample has an impurity in it, the melting point range will be lower and broader than the reported value. that's because an impurity will interfere with the bonding network in the solid.

I see that you've started out with 75mL of coffee, so you must have 75 mL , 75 grams of Coffee. 194.4 grams would imply that there's some type of impurity. maybe you didn't add enough drying agent.


I think I see a potential error.

WAIT DID YOU LEAVE YOUR SAMPLE IN A VIAL?

Answer 19

that number is way too big.

IF SO, you need to MEASURE THE MASS OF THE VIAL FIRST THEN SUBTRACT IT FROM THE MASS OF THE COMPOUND AND THE VIAL then you get the mass of caffeine.

Answer 20

sorry for the caps lol

Answer 21

I cant get the weight then until the it's dried though lol

Answer 22

That's why it's in my drawer still

Answer 23

\[194.4( Caffeine + Vial) -Vial,Grams = mass, caffeine \]

Answer 24

@Cimberjackson Not necessarily, did you take the mass of the vial before you put your sample in it?

Answer 25

I took the mass of the 100 mL round bottom flask because he asked for it for some reason

Answer 26

Was that what you put your final sample in after your lab was finished?

Answer 27

No, it was a 15 mL vial

Answer 28

Get the mass of the 15 mL vial when you go to lab

Answer 29

so i'm going to assume that your 194.4 grams is the mass of your sample inside of that 15ml flask right?

Answer 30

you took the mass of both of those things right?

Answer 31

I think i calculated the mass instead of scaling it

Answer 32

your original sample had

1 gram/mL density

and you started off with 75mL so you have 75 grams of coffee.

the number you have is too big 194, that cant be right because that's more than the entire sample.

that's why I was asking you if you had measured the mass of the sample inside of the vial.

that's a common mistake in lab but its fixable.

When you get back to lab I would do these three things.

1. remeasure the mass of your dried sample inside of your 15mL vial.
2. get another 15 mL volume with nothing in it and measure that.
3. find the difference between 1 and 2 and you'll get the mass of caffeine.

Answer 33

Thank you :)