[gusdub]

Please help.

I haven't taken physical chemistry yet (that's next term) but I am required to use that knowledge for something I'm doing now. I am supposed to design an experiment and it requires that I know c1v1=c2v2 but it totally isn't working for me. I must be missing something big.

My problem. I want to make a caffeine solution as a treatment and my control is already made (no caffeine).

for my control I am using 150g of sugar with 370 ml of distilled water. This is suppposed to give me a 30% sugar solution.

for my treatments I want to make 0.1 M caffeine solution, 0.01 M and 0.001 M

I got this advice for a friend but again not helping...
For a target Caffeine concentration of 0.1mM we first make a stock solution with 1g of Caffeine in 1L of distilled water, and then we pipette 0.0073277 L from this into a 0.37L sucrose solution (regular 30% sugar water solution). In order to adjust for the additional volume, we also add an additional 2.9g of sugar to the sucrose/caffeine mixture solution. This was all calculated using C1V1=C2V2 formula. I'm not sure what the values would be for 0.01mM caffeine but you guys can figure that out.

I know I looked at caffeine molarity and its 194.14 g per M ... but I need to adjust for the sugar solution to be 30% across all treatments...how do I do this? p.s. I need to make about 1 L worth of this solution and then I'll distribute it to 4 small vials.

Please any help is greatly appreciated.

[Borek]

for my control I am using 150g of sugar with 370 ml of distilled water. This is suppposed to give me a 30% sugar solution.

28.8%, not 30%.

For a target Caffeine concentration of 0.1mM we first make a stock solution with 1g of Caffeine in 1L of distilled water, and then we pipette 0.0073277 L from this into a 0.37L sucrose solution (regular 30% sugar water solution).

Why 0.37 L? Do you assume the volume didn't change? That's wrong, your solution is closer to 460 mL now.

In order to adjust for the additional volume, we also add an additional 2.9g of sugar to the sucrose/caffeine mixture solution.

Nice tray, but you were already off by over 1%, 2.9 g is not going to change the situation substantially.

I know I looked at caffeine molarity and its 194.14 g per M

This is molar mass, not molarity.

but I need to adjust for the sugar solution to be 30% across all treatments...how do I do this?

How precisely 30%? If ±1% doesn't matter, volumes of the caffeine solution that you will be adding won't matter much.

p.s. I need to make about 1 L worth of this solution and then I'll distribute it to 4 small vials.

1 L means four 250 mL vials, I would not call them small by any means.

[magician4]

if you are worried about exact concentrations of sugar after adding caffeine to the solution, you also should start by calculating the initial concentration of sugar correctly: 150 g in (150 + 370g) equals w ~ 28.8 %  ( and not 30%)

second, caffeine has a limited solubility in water (i.e in waterbased, diluted sugar solutions, too) : 20 g per liter of pure water (20°C), i.e. approx 0.1 mole / L max  (M = 194,19 g/mole)
the density of a w=30% saccarose solution is 1,1270 g/mL , so with 158,57 g sugar and 370 g ( = mL) water  around (which is a for real w=30% solution, V = 469 mL) you might come short on water
  it might become difficult to create a 0.1 mole/L caffeine solution thereof, and you need to test this first

but let's say for a moment this would work:you still can't calculate your desired composition precisely, as "mole/L " is density dependant ( which, again, is temperature dependant, additionally): you'd need density tables for caffeine/sugar/water systems for that

as I doubt that those are easily available, most probably you'd need to create those on your own, in the desired range.

however, if you're not in for exact values, you might also prepare a stock solution of ~ the desired concentrations/contents, and dilute accordingly

with low conc. of caffeine, these differences should be negligible. At 0.1 M and 0.01 M , however , this might give you some % off

it's up to you


regards

Ingo

[Borek]

you'd need density tables for caffeine/sugar/water systems for that

as I doubt that those are easily available, most probably you'd need to create those on your own, in the desired range.

At 0.1M caffeine presence won't change the density by more than single % (if that much). And actually I am not sure if it is intended to be 0.1M or 0.1mM, as the original post sometimes speak about M and sometimes about mM, and the described procedure yields mM range. Most likely sucrose solution density is all that is needed.

Actually such calculations are something that one of my calculators was written for:

<a href="http://www.youtube.com/v/6YxGrkNlmdU" target="_blank" rel="noopener noreferrer" class="bbc_link bbc_flash_disabled new_win">http://www.youtube.com/v/6YxGrkNlmdU</a>

At first I am calculating molar concentration of the 1g/L caffeine solution, then I am preparing recipe. Caffeine is not in the database, so it has to be entered manually.

[magician4]

At 0.1M caffeine presence won't change the density by more than single % (if that much).

of course you're right here
however, if we'd look at the w of sugar under those conditions, the influence would be bigger if we dealt with m(sugar) : (m(sugar) + 370 g + approx 20 g caffeine) here: -5% , ballpark , I estimate

And actually I am not sure if it is intended to be 0.1M or 0.1mM,

if we're talking mmolar conc., this whole discussion ref. densities, partial molar volume... would be meaningless, I agree:
just add a respective mass of solid caffeine to sugar/water w=30% , to gain a stock solution (and prepare mixtures with caffeine free w=30% solution thereof), and be done with it


regards

Ingo

[gusdub]

Ingo and Borek thank you so much. You guys are awesome.

I'll explain some more because there was a difference between your replies which demands a more clear explanation from myself. This is for an experiment to determine arthropod behavior and it deals with pollinators who visit plants for nectar rewards. My group is looking into testing the effects of caffeine laden nectar on learning behaviour. So we are setting this up and all we need left to calculate is the dosages and solutions. So we think .1 M will be likely to have 'aversive' effects and that 0.001 M (low treatment) will have some response that not as negative as .1 M, hence setting this up was a pickle to say the least. Moreover, our control is 30% or as you guys rightly showed 28.8% sugar solution. We wanted to make it so our treatments also have 30% sugar solution but to adjust for the caffeine. We will make the solution before giving it to the athropods. It will be at room temperature or just below it. However, never will it be raised above 21 celsius.

I owe you both a beer.

Where to send?

[Borek]

As magician already stated - caffeine solubility is listed as 2 g per 100 mL of water - that's around 0.1M. You will be dissolving it in a 30% sucrose solution, so there is no guarantee you will be able to get so high with the concentration.

Won't the 0.1M solution kill the insects?

You won't be able to prepare 0.1M solution using the approach suggested to you (1g in 1L of water) - as the concentration of the caffeine solution is an order of magnitude lower than the target solution.

[billnotgatez]

From WIKI

Extreme overdose can result in death.  The median lethal dose (LD50) given orally, is 192 milligrams per kilogram in rats. The LD50 of caffeine in humans is dependent on individual sensitivity, but is estimated to be about 150 to 200 milligrams per kilogram of body mass

While looking for the LD50 for bees, I found this paper.
It seems they did a similar experiment with sugar and caffeine
I had trouble figuring out the LD50 for bees from below
http://brage.bibsys.no/umb/bitstream/URN:NBN:no-bibsys_brage_32451/1/merged_document.pdf

GOOGLE and WIKI are great resources if you are lucky

[gusdub]

hmm, that's a cool paper thanks. Yes, well we expect an aversive reaction in the insects from the high dose treatment (0.1 M) and our lower limit of 0.001 M we expect some sort of measurable response.

If the 0.1 M is not possible to do under our conditions, what would you recommend as a reasonable high dosage? The 0.001 is still a go though?

Best

Gus

[Borek]

I would start checking what are typical concentrations of caffeine in plants and use concentrations in the same ballpark.

No problem with finding data on caffeine in dry tea (or coffee) but you would need to look for data about the fresh plant. Or, find the information about how much water does the drying plant loose.

[gusdub]

I see, yes however, for our purposes (this is not going to be published but is for a class project to test behaviour - and in our case - foraging) they are not extensive and we do not know all the flora that our pollinator is responsible for pollinating in our locality. Hence, why this is a short and simple project just to look if there is some positive response in foraging behaviour which could in the real world (doesn't have to though) represent some antagonistic selection (or mutualistic depending on context and perspective).

This is definitely an ecological and evolutionary study. I am quite interested in the chemistry I just wish I took physical chemistry BEFORE this course as it would have helped my understanding of the microscopic explanations of macroscopic phenomena.

We have decided to use 0.001 M (low) and 0.7 M (high) I wonder which program you're using for doing such calculations...that is really handy? Can you help out again with this please.

We are using artificial flowers and spreading out the treatments across 6 vials ... thinking that about 100-250 ml per vial (artificial flower) of the treatment and control (sugar solution). We will look to see if there is a preference by using spectro apparatus and assessing dye composition to quantify if there is a preference. Next thing we are doing is looking at motivation (learning).

I know this is not publishable because our sample size is low (n=3) we also have a time constraint. Our project expectations by the instructor was just to design an experiment to test behaviour and this is what we are doing...I know its not something from which we can make a real inferences from but we will give a good discussion and presentation and review previous literature of course and implications thereof.

Our greatest challenge has been deciding concentrations for this experiment...been a little bit of a head-scratch (or head ache hehe) but I thought where better to go for help then here and you guys have been really helpful and I really appreciate that.

I like your quote - I am occasionally known to be wrong. My quote should be I am rarely known to be right...time proves me wrong this leads inevitably closer to what is right.

Best

Gus

[Borek]

We have decided to use 0.001 M (low) and 0.7 M (high)

0.7M is out of the question, caffeine is not that soluble, we told you that several times already. 0.1M at best.

I wonder which program you're using for doing such calculations...that is really handy? Can you help out again with this please.

http://www.chembuddy.com/?left=CASC&right=concentration_and_solution_calculator

(there is a free 30-days trial - slightly limited, but you will be able to do all necessary calculations using it)

[gusdub]

Sorry I meant to say 0.07 M to make it under .1 M, my apologies. Thanks for the link.