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### Topic: Need some help, Not homework!!!  (Read 3456 times)

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#### zeshkani_usa

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##### Need some help, Not homework!!!
« on: January 20, 2012, 09:07:16 PM »
Hi there,

I was just going through my old analytical chem book, and i was just flipping through and saw this problem

"Calculate how much of each of the stock reagents listed below should be used to make 100mL of homogenization buffer containing:
10mM Tris pH8.6(dilute 50mM stock)
1mM PMSF (dilute 100mM stock)
1mM EDTA (dilute 20mM stock)
0.2uM pepstatin A (dilute 20uM stock)
1mM 2-mercaptoethanol (dilute 7.1M stock)

okay so this is what i get from this, with these 5 ingredients, all of these need to add up to 100mL

is this problem as simple as using Molarity=Moles/Volume   or using C1xV1=C2xV2

I would appriciate it if someone can direct me in the right direction, on how to approach this problem

Thx

#### Arkcon

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##### Re: Need some help, Not homework!!!
« Reply #1 on: January 20, 2012, 10:09:22 PM »
Both really.  The units are Molarity, milli- and micro-, so you will use moles per liter.  The thing is, you could never weigh out micro-moles of something with sufficient accuracy, so once you've prepared the suggested stock solutions, you will use C1V=C2V2 to make your solution.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

#### zeshkani_usa

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##### Re: Need some help, Not homework!!!
« Reply #2 on: January 21, 2012, 12:08:46 AM »
okay i think i got it figured out here are my values calculated for each ingredient:

this totals to = 27.014mL -100mL(total)= 72.9mL of H2O

does this seem right?

#### Borek

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##### Re: Need some help, Not homework!!!
« Reply #3 on: January 21, 2012, 04:30:08 AM »
all of these need to add up to 100mL

That's assuming your lab doesn't have water to fill it up to the mark. Rather unlikely assumption
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