Science/mathematical question, maybe ATTN: Nigel

[Nephew Twiddleton]

So, before we do the lab we have to do a lab skills test prior to. I don't want the answers, I just want to know how to set shit up, because, I'm really not getting it. I've got half the answers and have no idea if I'm correct, so if you can tell me if I am and if I went about it the right way, then bully. It's all molarity shit, so I imagine it's pretty basic for someone who has taken chem, but I have not taken chem.

1. Calculate the amount of Tris [Tris(Hydroxomethyl) Aminomethane] needed to make 500 ml of a 1 M stock solution. MW=121.14.
Answer I got: 60.57 grams. Formula: MW*mol*volume

2. Calculate the amount of EDTA (ethylenediamine tetraacetic acid, disodium salt) needed to make 500 ml of a 0.5 M stock solution. FW=372.2
Answer I got: 93.05 grams. Same formula as above.

3. Calculate the total volume of  solution needed to get an 80% solution from 100 ml of 95% ETOH (Ethanol). [Note: Use absolute (100%) ethanol, but be aware that shortly after the bottle is opened, absolute ethanol becomes 95%. If a bottle has been opened, calculate the total volume of solution needed to get an 80% solution from 100 ml of a 95% solution.]
118.75 ml (I'm thinking this is wrong, whereas I'm pretty sure about the above two). Formula: Concentration of stock agent/final concentration needed=Final volume needed/volume of stock reagent. Which is a formula given in the lab manual.

4. You have 300 ul [sic. I'm assuming microliters] of DNA solution in TE buffer. You wish to add salt to precipitate your DNA. You have a 3M NaOAc  solution. You wish to bring your DNA solution to 0.3M NaOAc.
No clue.

5. How much solute is required to make 300 ml of 0.8 M CaCl₂?
I imagine I use a variant of the formula in 1 and 2.

6. How would you prepare 500% (w/v) solution of NaCl?

[Mesozoic Mister Nigel]

I have to go take a final in 15 minutes so I'm gonna kind of rush through these.

#1 & 2, yes. Molarity of a solution is moles of solute per liter of solution.

#3. Use the formula given and you're fine, make sure you convert any concentrations given in L to mL. That's a good one to solve with dimensional analysis to make sure you clear all your unwanted units.

#4. µl is microliters, yes. You're just going to do the above again to figure out how much NaOAc to use.

#5. Yes, find the molar weight of CaCl2 and proceed from there.

#6. Same as #5.

I hope this was in some way helpful, if not I'll be back in about two hours if you have any questions!

[Mesozoic Mister Nigel]

Oh, if you haven't gone over dimensional analysis yet, this might help! http://www.youtube.com/watch?v=DsTg1CeWchc

[Reginald Ret]

I'll try to help without giving answers.

3. Maybe the equation makes more sense to you if the formula given in the lab manual is written down differently:
Concentration of stock reagent*Volume of stock reagent = Final concentration needed* Final volume needed

4. Every molecule with at least one metal atom and at least one non-metal atom is a salt, that makes NaOAc a salt.

5. You will be expected to look up MW later, but judging from the earlier questions that is not yet the case. They did not define weight, they merely asked for how much. So you give the answer in mole instead of in weight.

6. The weight of water is 1 gram/ml, and they ask for a 500% w/v solution. So weightwise you need 5 times as much NaCl as water.<sup>1


1</sup> That would only be possible in a highly heated container. You will want to make sure the container is pressurized as well because at the temperatures required to dissolve 500gram NaCl in 100ml water, water tends to go POOF. (I'm not even sure if you can reach those temperatures before your solution becomes plasma.)

Addendum: Nigel has me worried about  5 and 6, take her word over mine, her knowledge is fresher. Also, i'm pretty sure she is smarter than i am.

[Nephew Twiddleton]

Thanks, thanks, and thanks!

[Nephew Twiddleton]

I typed down 6 wrong:

How would you prepare 500ml of a 5% (w/v) solution of NaCl.

But I imagine the principle is the same anyway.

[Mesozoic Mister Nigel]

Regret, I bet you're right about being able to give the answers to 5 and 6 in percent moles, I didn't think about that. Thanks for the compliment though!

Twid, is this for 221, or is it a prep or medical course? What book are you using? I was a little thrown off by the percent solution, because we weren't taught percent solution, but then I figured that it refers to molarity... am I right? If yes you can right away convert it to molarity.

Unless you happen to be a chemistry savant, this stuff is really hard and takes a lot of time to really get down; even my friend Bijijoo, who is one of the two smartest people I've ever known and has a PhD in biophysical chemistry, struggled with general chemistry. So, anything I can do to help, let me know and I'll try my best, presuming I don't forget it all as soon as I take the ACS exam tonight.

[Nephew Twiddleton]

Regret, I bet you're right about being able to give the answers to 5 and 6 in percent moles, I didn't think about that. Thanks for the compliment though!

Twid, is this for 221, or is it a prep or medical course? What book are you using? I was a little thrown off by the percent solution, because we weren't taught percent solution, but then I figured that it refers to molarity... am I right? If yes you can right away convert it to molarity.

Unless you happen to be a chemistry savant, this stuff is really hard and takes a lot of time to really get down; even my friend Bijijoo, who is one of the two smartest people I've ever known and has a PhD in biophysical chemistry, struggled with general chemistry. So, anything I can do to help, let me know and I'll try my best, presuming I don't forget it all as soon as I take the ACS exam tonight.

This is, surprisingly, for Genetics. Which is why I'm suddenly like, "wait, what?"

The stuff in the lab manual isn't terribly intuitive. Throw on top of that it's all word problems pertaining to chemistry and I'm like, "shit...."

[Nephew Twiddleton]

As far as the book, the text book we're using is Essentials of Genetics/masteringgenetics.com, and the lab manual is just the standard manual for Genetics at BHCC.

Note, however, only one professor teaches Genetics at BHCC.

[Mesozoic Mister Nigel]

Ohhhh, it's for Genetics! I was really thrown for a loop by the percent solution and the weight/volume, but now it makes sense! Sorry, I hope I didn't add too much confusion to the mix.

[Nephew Twiddleton]

Ohhhh, it's for Genetics! I was really thrown for a loop by the percent solution and the weight/volume, but now it makes sense! Sorry, I hope I didn't add too much confusion to the mix.

No worries! I was just a bit surprised by the whole thing, since chem isn't a prereq. Obviously. 

[Mesozoic Mister Nigel]

Ohhhh, it's for Genetics! I was really thrown for a loop by the percent solution and the weight/volume, but now it makes sense! Sorry, I hope I didn't add too much confusion to the mix.

No worries! I was just a bit surprised by the whole thing, since chem isn't a prereq. Obviously. 

They might do the nice thing for the first lab and walk the class through the prelab. Here's hoping.

[Nephew Twiddleton]

Ohhhh, it's for Genetics! I was really thrown for a loop by the percent solution and the weight/volume, but now it makes sense! Sorry, I hope I didn't add too much confusion to the mix.

No worries! I was just a bit surprised by the whole thing, since chem isn't a prereq. Obviously. 

They might do the nice thing for the first lab and walk the class through the prelab. Here's hoping.

We have to submit it online tomorrow and first lab is Wednesday.

[Mesozoic Mister Nigel]

Oh, also, this might be kind of useful: http://www.youtube.com/watch?v=AN4KifV12DA

In fact, if you have time, #1 through #11 might make a nice primer. And also #27: http://www.youtube.com/watch?v=9h2f1Bjr0p4

[Mesozoic Mister Nigel]

Ohhhh, it's for Genetics! I was really thrown for a loop by the percent solution and the weight/volume, but now it makes sense! Sorry, I hope I didn't add too much confusion to the mix.

No worries! I was just a bit surprised by the whole thing, since chem isn't a prereq. Obviously. 

They might do the nice thing for the first lab and walk the class through the prelab. Here's hoping.

We have to submit it online tomorrow and first lab is Wednesday.

Well, that's lame.