[darkryder341]

Hello everyone...


Well, I need some help. I'm stuck on this one problem. I recently did a chem lab on Beer's Law and what I'm trying to find is the mass of alcohol (CH3CH2OH) in a litre of vodka.

Here's all the information I have:

- mol CH3CH2OH (calculated by finding mol of Cr3+ and using mol ratio to convert to CH3CH2OH) = 5.08125*10^-4
- [CH3CH2OH] in 25 mL volumetric flask = 0.020325 M
- [CH3CH2OH] in dilute vodka sample (used 2.5 mL of diluted vodka) = 0.20325 M
- [CH3CH2OH] in undiluted vodka sample = 8.13 M (diluted vodka was 1/40, so I multiplied 0.20325 * 40)

Here's where I'm stuck:

It asks for me to calculate mass of CH3CH2OH in 1 L of vodka. So I thought I would go:

mol = c * v = 8.13 * 1 = 8.13 mol CH3CH2OH and then somehow try to convert to mass....but I don't think that's right, because in the next question it asks for me to convert this mass into a volume of CH3CH2OH in 1 L of vodka and gives me the density = 0.798 g/mL^-1....

It's just, I'm not given the molar mass for CH3CH2OH and I didn't think density was the same as molar mass...unless I'm supposed to use the molar mass of Cr3+?...

I'm a little confused...I'd really appreciate any help because I can't seem to find anything on the net that answers this question =\ If I forgot to include any info, let me know. Thanks!

EDIT: I looked up the molar mass of CH3CH2OH and found that it was 46.07 g/mol. Would I just multiply 8.13 mol * 46.07 g/mol to get 374.5 g? Is that right?
EDIT2: Nevermind, solved it. I was right about what I asked above.

[Aqueous Maqueous]

I'm pretty sure you can find the mass by getting the density. Figuring out the density of Vodka at room temperature is beyond me. It'd be easier to just drink it.

[Borek]

Density of the solution has to be checked in tables. Molar mass can be easily calculated for a given formula, that's chemistry kindergarten, no need for looking it up.