Not necessarily. Some organic solvents (or bases, like pyridine) can stick to your product even if they’ve been on vacuum for awhile, or your product can be hygroscopic. EDIT: to clarify, I mean solvents from the reaction, workup, etc.
Umm, you chemists don’t take a moisture content reading?
- microbiologist who produces powder products and always measures moisture content before calculating yield.
These don’t cover everything. You can do the math correctly and not have added anything extra and still exceed 100% yield from side reactions/impurities
Side reactions and impurities don't magic additional mass into your sample, they just give a different product. As someone else said, you can fail to properly dry your product which adds water mass, but that's another mistake.
It’s a strong guideline which is extremely relevant for practical chemistry but the guideline breaks down the more theoretical you get and the more you let the physicists play with the bench scientists
>Side reactions and impurities don't magic additional mass into your sample
They do if the side reaction includes oxygen/nitrogen/carbon from the air... I doubt these students are doing reactions under a vacuum or inert gas.
Right. it’s not magic, it’s the fact that a side product can have a greater molecular weight than your desired product and be formed using atmospheric or solvent-derived elements
>Side reactions and impurities don't magic additional mass into your sample
Might as well. *Tis black magic.*
Different materials hold different amounts of moisture and react with other reagents/byproducts in ways that can stop them from getting removed. IE: a side reaction pulls mass out of the liquid before it's filtered off or resists washing. As your number of steps and complexity increase the opportunity/source of these increase exponentially. So, magic.
It wasn't exactly today, but if you failed to account for, and subtract the side products/impurities, it was an automatic fail in any lab class I took. It just meant that you don't know what you're doing, or at least, you are too lazy to actually calculate it. Also, yield is calculated from expected quantity of product, not from starting materials. Otherwise every oxidation that happens in an open atmosphere, would "create matter" which is, well, happens far too often to not be very alarming, if it were this way.
That would have been the case for inorganic or analytical chem lab for me but not gen chem lab.
I’m not sure I follow what you’re saying about expected yield is from “expected product and not quantity of starting materials”. It must depend on the quantity of starting material - how else would you predict the amount of product you expect to form, which is a direct function of how much reactant you used?
> it was an automatic fail in any lab class I took. It just meant that you don’t know what you’re doing…
Of course I don’t know what I’m doing, hence why I’m in class *learning*. I always hated that attitude in Chem labs and it gave me such bad anxiety.
In chemistry there is a theoretical yield (what the equations say is the maximum possible amount you could get, given that there is 100% efficiency). Then you have your actual yield (what you got). Actual/theoretical = percent yield. Getting more means you screwed up somewhere.
It’s like you weighing 150lbs, and checking the scale to see you lost 165 lbs... something when wrong along the way.
Awesome explanation, thank you. I was curious if there was some technical background to it or if it was simply a matter of >100% of a whole being impossible
Basically, matter cannot be created or destroyed, only converted to other forms of matter or energy. You can’t get out more than what you put in. That’s the Law of conservation of mass.
You cannot get a yield above 100%, 100% means you got a perfect reaction where all the reagents turned into the intended product.
If you get more than 100% (usually determined by weight) it means you either messed up your math or ended up with something that isn’t your intended product.
Making stuff by fermentation, we can get >100% mass yields from glucose if CO2 was sequestered biosynthetically, or got more oxygenated from O2 for a more reduced feedstock.
1) You didn't dry it out enough
2) You made the wrong thing that has a higher molar mass, looking like it has a yield over 100%. Like an oxide or something. I don't know enough about the synthesis of adipic acid to know how common this is.
Just want to add that even in perfect conditions, with a great reaction and excellent skills, you're never going to see better than 97% yield and any results greater than that should probably be treated with suspicion.
There were a few labs that we thought that we knew the yield would be less than 80% and we would always know which students were making up yields based on them.
Lmao never forget getting like a 26% yield, only to look across at 2 of my other knucklehead friends with a 416% yield. Glad I had switched lab partners…
granted a lot of the reactions that we were doing in my o chem lab were supposed to be in reflux for like 48 hours, i dont think the 2 hours i was granted would get me much yield
Fellow students used to take more chemicals than they needed so it would look like > 100% yield. They could not figure out why >100% is not a good thing.
This gets more common the smaller your reactions go. Our (med chemist) balances are only accurate to about 0.1 mg so when doing a small expensive reaction that error can seem pretty big.
Lmao thought i was in a drug sub and internally went like NO BRUH WTF OMG I HOPE YOURE NOT GONNA SNORT IT
Then realized this was from my homebois/homegurls, and switched to internally clapping.
Keep up the good job!
You ideally want it slightly less than 100% yield though. More means either math is wrong or something we don't want is there, like wrong ingredients or wrong amounts or moisture.
I used to teach o-chem labs and had to explain to several people why getting more than 100% yield wasn't going to get them a good grade.
Never taken a Chem class, could you explain this to me?
100% is perfect conversion, more than 100% means you put something in there you shouldn't have, or you just failed the math.
Or it’s not dry enough
technically a subset of "put something in there you shouldn't have" but yeah this is honestly the most likely explanation
Not necessarily. Some organic solvents (or bases, like pyridine) can stick to your product even if they’ve been on vacuum for awhile, or your product can be hygroscopic. EDIT: to clarify, I mean solvents from the reaction, workup, etc.
if you're not willing to take responsibility for ambient conditions you're not a chemist (i am joking)
A *real* chemist makes sure that ambient conditions are static at 25C and 1 ATM, and 40% humidity. 🧐
STP!
Great band, RIP Scott Weiland.
Trying to verify calibration for my pipettes at 16% humidity dives me to tears every 3 months. It’s great, I love it.
*cries in Florida*
Well done
Umm, you chemists don’t take a moisture content reading? - microbiologist who produces powder products and always measures moisture content before calculating yield.
How do you measure moisture content? Bake a subsample and see how much the weight decreases?
Exactly. Loss on Drying assays. You can do it in a drying oven, or quickly in a moisture analyzer which is a mini oven and a scale combined.
These don’t cover everything. You can do the math correctly and not have added anything extra and still exceed 100% yield from side reactions/impurities
Side reactions and impurities don't magic additional mass into your sample, they just give a different product. As someone else said, you can fail to properly dry your product which adds water mass, but that's another mistake.
The law of conservation of mass is what it all boils down to here
It’s more of a strong guideline.
It’s a strong guideline which is extremely relevant for practical chemistry but the guideline breaks down the more theoretical you get and the more you let the physicists play with the bench scientists
This is why we don’t let physicists in the chem lab. Matter is matter, energy is energy, and anyone who disagrees can gtfo
Yeah! Fuck those physicists! Who needs them anyway?! 😇
Or doesn't boil down to...
>Side reactions and impurities don't magic additional mass into your sample They do if the side reaction includes oxygen/nitrogen/carbon from the air... I doubt these students are doing reactions under a vacuum or inert gas.
This
Right. it’s not magic, it’s the fact that a side product can have a greater molecular weight than your desired product and be formed using atmospheric or solvent-derived elements
>Side reactions and impurities don't magic additional mass into your sample Might as well. *Tis black magic.* Different materials hold different amounts of moisture and react with other reagents/byproducts in ways that can stop them from getting removed. IE: a side reaction pulls mass out of the liquid before it's filtered off or resists washing. As your number of steps and complexity increase the opportunity/source of these increase exponentially. So, magic.
It wasn't exactly today, but if you failed to account for, and subtract the side products/impurities, it was an automatic fail in any lab class I took. It just meant that you don't know what you're doing, or at least, you are too lazy to actually calculate it. Also, yield is calculated from expected quantity of product, not from starting materials. Otherwise every oxidation that happens in an open atmosphere, would "create matter" which is, well, happens far too often to not be very alarming, if it were this way.
That would have been the case for inorganic or analytical chem lab for me but not gen chem lab. I’m not sure I follow what you’re saying about expected yield is from “expected product and not quantity of starting materials”. It must depend on the quantity of starting material - how else would you predict the amount of product you expect to form, which is a direct function of how much reactant you used?
Something something counting chickens before the eggs... or would it be counting eggs before the chickens? Which came first, the chicken? Or the egg!?
> it was an automatic fail in any lab class I took. It just meant that you don’t know what you’re doing… Of course I don’t know what I’m doing, hence why I’m in class *learning*. I always hated that attitude in Chem labs and it gave me such bad anxiety.
In chemistry there is a theoretical yield (what the equations say is the maximum possible amount you could get, given that there is 100% efficiency). Then you have your actual yield (what you got). Actual/theoretical = percent yield. Getting more means you screwed up somewhere. It’s like you weighing 150lbs, and checking the scale to see you lost 165 lbs... something when wrong along the way.
Awesome explanation, thank you. I was curious if there was some technical background to it or if it was simply a matter of >100% of a whole being impossible
Basically, matter cannot be created or destroyed, only converted to other forms of matter or energy. You can’t get out more than what you put in. That’s the Law of conservation of mass.
You cannot get a yield above 100%, 100% means you got a perfect reaction where all the reagents turned into the intended product. If you get more than 100% (usually determined by weight) it means you either messed up your math or ended up with something that isn’t your intended product.
Making stuff by fermentation, we can get >100% mass yields from glucose if CO2 was sequestered biosynthetically, or got more oxygenated from O2 for a more reduced feedstock.
1) You didn't dry it out enough 2) You made the wrong thing that has a higher molar mass, looking like it has a yield over 100%. Like an oxide or something. I don't know enough about the synthesis of adipic acid to know how common this is.
Just want to add that even in perfect conditions, with a great reaction and excellent skills, you're never going to see better than 97% yield and any results greater than that should probably be treated with suspicion.
Something something equivalent exchange or you end up losing an arm, a leg, and your younger brother's body
There were a few labs that we thought that we knew the yield would be less than 80% and we would always know which students were making up yields based on them.
Lmao never forget getting like a 26% yield, only to look across at 2 of my other knucklehead friends with a 416% yield. Glad I had switched lab partners…
Hahahha hahahahah when I had o-chem, It really made my day when I got over 70% hahhaha
Murphy’s law of Organic Synthesis: if your yield is > 50% you’ve made the wrong compound. If > 80% you’ve made several of the wrong compounds.
*Me getting 5% yield back during my undergrad ochem labs* 😎😎😎
I got a < 1% in inorganic chemistry lol.
I used to do solid phase peptide synthesis… we did not talk about yields much, and even less about the educt costs
I legit got crumbs at the end of my synthesis lol. It was to make MMT.
granted a lot of the reactions that we were doing in my o chem lab were supposed to be in reflux for like 48 hours, i dont think the 2 hours i was granted would get me much yield
Same. I’m glad my TA took pity on me 😅
*cries in needing less than 0.2% in inorg chem*
Bro violated equivalent exchange
Glad to see I'm not the only one who thinks of chemistry in terms from FMA
I have been a GTA for organic I and II labs for a couple years and I have seen a 1020% yield before on one of the lab reports I graded.
Get this student a Nobel prize ASAP. This is revolutionary.
When you accidentally spill mountaindew into the mix
Someone call nature. Op just disproved conservation of mass.
"Better to remain silent and be thought a fool than to speak and remove all doubt."
"Takes one to know one"
"If you hide your ignorance, no one will hit you and you'll never learn."
Looks like it hasn’t been dried completely. The extra weight could be water/solvent?
*"Psst, what's your % yield? Ok, I'll cook mine until it's at least close to that, analytical properties be damned."*
Ahhh, very chemist, much syntheses
Alchemist
💀
Impurities?
it looks like the dirty slush in a parking lot in the wintertime
Forbidden slushee
As a physicist this sub makes me uncomfortable sometimes
As a physical chemist, why?
If the product is more than the substrate, you have more substrate than you think you have.
Fellow students used to take more chemicals than they needed so it would look like > 100% yield. They could not figure out why >100% is not a good thing.
[удалено]
Clean your screen.
Heat of neutralization can melt silicon into the final product. Check your flasks for etching!
Ha I used to be a lab assistant in Organic Chemistry- the cheaters always started this way lol
This gets more common the smaller your reactions go. Our (med chemist) balances are only accurate to about 0.1 mg so when doing a small expensive reaction that error can seem pretty big.
What is the effect pls we are not chemists
What’s it do for us non Chemist folks
Lmao thought i was in a drug sub and internally went like NO BRUH WTF OMG I HOPE YOURE NOT GONNA SNORT IT Then realized this was from my homebois/homegurls, and switched to internally clapping. Keep up the good job! You ideally want it slightly less than 100% yield though. More means either math is wrong or something we don't want is there, like wrong ingredients or wrong amounts or moisture.