Calculating the mass of 3 ml 0.5N methanolic NaOH.

[Sandra7]

Hi,
I prepared 0.5 N methanolic NaOH weighing .2g of NaOH into 10 ml of MeOH. It took NaOH quite some times to dissolve.

I used 3 ml of this methanolic solution to mix with 0.08 g (80 mg) o extra virgin olive oil to perform saponification before derivatizing the mixture (olive oil + NaOH) with 12% (1.5M) BF3.

How would I go about calculating the mass of 3 ml methanolic NaOH used in saponification since I could see that the .5N mathanolic NaOH was a bit saturated? I took 3 ml of methanolic NaOH, making sure that the solid pieces of NaOH were left behind.

MW of NaOH = 39.99 g/mol

Density of NaOH = 2.13 g/ml

[Consumer Products Guy]

We also make up 0.5 M NaOH in methanol, it does take a while. I think the undissolved stuff is mostly sodium carbonate though. We compensate for the NaOH being 85% pure.

As to the density of the solution, you know the grams, can't you just dissolve up same in a stoppered graduated cylinder and measure the final volume?

[Peter Apps]

KISS - take another 3 ml from the approx 7 ml that you have left over, and weigh it.

What is this "N" ?

Peter

[DSP007]

Hello, well take a graduated cylinder at 10 ml and make three to 10 ml of 0.5 M solution - dissolve 0.2 g in 9 ml of methanol and methanol to bring the volume to 10 ml. Enough just on three parallel samples. Accuracy of preparation of this solution does not play a special role is reactive to saponification of fat. Plus-minus kilometer.

[DSP007]

KISS - take another 3 ml from the approx 7 ml that you have left over, and weigh it.

What is this "N" ?

Peter

Hi
N- Normality of solution. Old termine from titrometry. C(mol/l) x Ionic activity (dissotiation factor) - for NaOH [0H-] in water -0.999 , for H2SO4 [H+ 2 const] in water 1.999(3).

From this quest N=M- precison of solution "plus- minus kilometer"

[HW Mueller]

Sandra7, you would have to titrate your NaOH solution to find out how much NaOH is in it. But what for (already questioned above)? Besides, weighing out 0.2 g of NaOH is not so hot . . . .
Why do you react with NaOH then BF3, transesterification with BF3/MeOH might do the trick for you.

[DSP007]

Besides, weighing out 0.2 g of NaOH is not so hot . . . .
Why do you react with NaOH then BF3, transesterification with BF3/MeOH might do the trick for you.

Good afternoon, HW Mueller.

1) Yes you can mix a solution in a bucket and spade for this purpose. But why then do with it so much? So IMHO 0.2 g of sodium hydroxide is just what the doctor ordered a pair of crumb or a Scale (granule).

2)Its Sandra methodology execute . Step right, step left - an attempt to escape, jumping in place provocation. (c) Although I myself do not like BF3 . IMHO ethyl esters is much nicer to work.

[Consumer Products Guy]

Why do you react with NaOH then BF3, transesterification with BF3/MeOH might do the trick for you.

Actually, HW, that would be what we do also. We've found that fats and oils (unlike fatty acid or soap samples) do not mix readily with methanol-BF3 or methanol-H2SO4, the triglyceride just sits on the bottom, not good contact with the methanol portion. So we saponify for 15 minutes, then acidify and heat a little to make methyl esters, have been doing this for three decades.

We haven't the need to try sodium methoxide or any fancy one-step reagents for this.

As to ethyl esters, one must use ethanol that contains no methanol or IPA denaturants, or you'll really get a mess. Fatty acid ethyl esters are typically used as retention index markers in the fragrance industry.

[HW Mueller]

CPG, do you have to work with such horrendously high concentrations for some reason?

[Consumer Products Guy]

No, we typically have lots of sample, take larger sample sizes to ensure homogeneity. When we do fats and oils, we use a 1 gram sample. With soaps or fatty acids, maybe 3 grams. We've done this for 35 years.

[chromatographer1]

You are correct when you say the oils do not mix well with BF3/methanol.

I have transesterified oils and fats by adding DCM or Chloroform to the BF3/Methanol and heated the mixture. Then I only had to add my salt water to extract my esters.

Never had a problem. Are there problems with doing this? I would love to learm if there is a problem.

best wishes,

Rod