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### Topic: Understanding Equivalents  (Read 9098 times)

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#### fledarmus

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##### Re: Understanding Equivalents
« Reply #15 on: August 29, 2012, 03:37:45 PM »
so i got the volume of acetyl chloride to be 1.0467 ml.

im lost at figuring out the volume of methanol.
i have 0.0489 mol of tryp (1000ml of solution/0.75 mol of tryptophan) = 6.52ml of tryp of solution

I did a little correcting on your equation. You do have to be careful of your units - M is not moles of your compound/liter of your compound, but moles of your compound/liter of solution. In your case, for 1 gram of tryptophan, you'll need about 6.5 mL methanol.

As Discodermolide says, you probably don't need that much methanol for the reaction, but in this case you're also using it for the solvent and tryptophan isn't particularly soluble in methanol at room temperature. For a reaction I don't know, I usually start somewhere on the order of 0.5M to 1.0M concentration in solvent as a first try, so I wouldn't think 0.75M is unreasonable.

#### viet

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##### Re: Understanding Equivalents
« Reply #16 on: August 30, 2012, 05:05:27 PM »
say i have a certain amount(#) of tryptophan-methyl-ester hcl (1eq) and put it in dichlromethane (0.18M)
i would have:
#g tryp-ome·hcl (1mol/204.3g tryp) = $mol tryp to find out how much dichlorometh needed: X ml 1000 ml -------------- = ----------- => X ml =$# ml of ch2cl2
## mol tryp       0.18 mol

is that right?

#### Borek

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##### Re: Understanding Equivalents
« Reply #17 on: August 30, 2012, 05:38:17 PM »
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

#### viet

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##### Re: Understanding Equivalents
« Reply #18 on: August 30, 2012, 10:17:30 PM »
sorry i couldnt modify the prev post due to different ip.

say i have a certain amount(#) of tryptophan-methyl-ester hcl (1eq) and put it in dichlromethane (0.18M)
i would have:
$$(an\,amount\,tryptophanmetholester·HCl) \frac {1mol}{204.3g\,tryp}) = X\,mol\,tryp$$
want to know how much CH2Cl2 needed:
$$\frac {unknown\,ml\,CH2Cl2}{X\,mol\,tryp} = \frac {1000ml\,soln}{0.18 mol\,CH2Cl2}$$
« Last Edit: August 30, 2012, 10:34:13 PM by viet »

#### fledarmus

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##### Re: Understanding Equivalents
« Reply #19 on: September 03, 2012, 11:18:01 AM »
sorry i couldnt modify the prev post due to different ip.

say i have a certain amount(#) of tryptophan-methyl-ester hcl (1eq) and put it in dichlromethane (0.18M)
i would have:
$$(an\,amount\,tryptophanmetholester·HCl) \frac {1mol}{204.3g\,tryp}) = X\,mol\,tryp$$
want to know how much CH2Cl2 needed:
$$\frac {unknown\,ml\,CH2Cl2}{X\,mol\,tryp} = \frac {1000ml\,soln}{0.18 mol\,CH2Cl2tryptophan}$$

Once again, your 0.18M is referring to 0.18 moles tryptophan/1000 mL solution.