[pacemaker]

I would like to confirm, when weighing the crude product, should the mass be higher than the mass once it has been recrystallized and dried for one week?

[Archer]

I would like to confirm, when weighing the crude product, should the mass be higher than the mass once it has been recrystallized and dried for one week?

Normally, yes.

There are some circumstances when this can happen.

Can you provide the following:

The substance

The solvent

The weights

The drying temperature.

[pacemaker]

I would like to confirm, when weighing the crude product, should the mass be higher than the mass once it has been recrystallized and dried for one week?

Normally, yes.

There are some circumstances when this can happen.

Can you provide the following:

The substance

The solvent

The weights

The drying temperature.

We hydrolyzed Methyl butanoate to make methanol and salicylic acid. The crude salicyclic acid was weighed, crystals were extracted by vacuum filtration and dried for one week. I don't know the drying temperature because the lab tech took the tray with our samples into the back room. When I weighed the recrystallized salicylic acid after one week (5.5 g), it was more mass than the crude (4.9 g). I am confused as to how this can happen and if I did something wrong in the experiment because I thought that the recrystallization and drying makes it more pure but we lose some of the mass as water soluble impurities dry out.

[Archer]

We hydrolyzed Methyl butanoate to make methanol and salicylic acid. The crude salicyclic acid was weighed, crystals were extracted by vacuum filtration and dried for one week. I don't know the drying temperature because the lab tech took the tray with our samples into the back room. When I weighed the recrystallized salicylic acid after one week (5.5 g), it was more mass than the crude (4.9 g). I am confused as to how this can happen and if I did something wrong in the experiment because I thought that the recrystallization and drying makes it more pure but we lose some of the mass as water soluble impurities dry out.

You mean methyl salicylate was hydrolysed?

You didn't provide the solvent used in the recrystalisation.

I think in this case it was either insufficiently dry or an error has occurred in weighing.

[pacemaker]

We hydrolyzed Methyl butanoate to make methanol and salicylic acid. The crude salicyclic acid was weighed, crystals were extracted by vacuum filtration and dried for one week. I don't know the drying temperature because the lab tech took the tray with our samples into the back room. When I weighed the recrystallized salicylic acid after one week (5.5 g), it was more mass than the crude (4.9 g). I am confused as to how this can happen and if I did something wrong in the experiment because I thought that the recrystallization and drying makes it more pure but we lose some of the mass as water soluble impurities dry out.

You mean methyl salicylate was hydrolysed?

You didn't provide the solvent used in the recrystalisation.

I think in this case it was either insufficiently dry or an error has occurred in weighing.

Yes, we used Methyl salicylate (my mistake) and NaOH was used as well.

So, the crude weight should be higher than the recrystallized weight? If that is not the case, its possible that the recrystallized product was not dried appropriately? Also, the recrystallized mass should be lower than the theoretical expected mass, based on the reaction equation (i.e. we used .03 moles of methyl salicylate and it was the limiting reagent, so theoretically we should expect 4.6 grams of the recrystallized product)? since the recrystallized weight is higher than the theoretical, it may be due to insufficient drying process? Do I have the logic/understanding correctly?

Also, just a methodology related question - Is the crude mass taken after vacuum filtration and before boiling it with water? or can we also take the mass of the crude product after we have boiled the sample and have done the vacuum filtration for a second time, right before leaving it to dry for one week?

Sorry about the naive questions, I am new to organic chemistry and it has been many years since I took gen. chem so doing chemistry labs now is a new experience.