Rookie Mistakes

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There are certain common sources of error responsible for ~90% of all first-year experimental failure. Here they are.


MistakeCheck the mistakes you have madeNumber of rookies who have done this
Forgot to stop a TLC before solvent reached top of plate. 687
Forgot to tare the flask. 635
Forgot to take the stopper off your separatory funnel and wondered why nothing was coming out. 501
"Lost" product while purifying it through column chromatography 494
Bumped product into filthy rotavap 469
Ran column dry 467
Poured a reaction mixture into a separatory funnel with an open stopcock. 420
Majored in Chemistry. 413
didn't label flask on same day, forgot what was in it 400
Took an NMR and saw only solvent peaks. 381
Thought a reaction was done when it wasn't- and isolated starting material. 325
Broke glassware whilst trying to clean it. 324
Was too lazy to dry the solvent. 302
Refluxed to dryness 285
Forgot to turn on condenser water supply. 281
Used all of an advanced intermediate on a single experiment 265
Used the wrong bottle of reagent or solvent during reaction setup 264
Did not take the purity of a reagent into account in amount calculation. 235
Made reaction without checking identity of starting material 235
TLC spotted below solvent level in chamber 225
Miscalculated by a factor of ten. 212
Broke the flask when scratching it. 206
Not enough volume left in flask to quench the reaction. 203
Believed an unbelievable procedure and spent days trying to repeat is, hoping it would 'save time' 177
Left an important compound on the bench/out of the fridge too long, found it had decomposed and had to make it again. 175
Put a round bottom in a large ice bath to cool and it fell over and filled with water 169
Forgot to weight flask before adding product in. 167
Forgot to add reagent 159
Hooked up water lines to a condenser backward 151
In case of product, break glass. 149
Discarded the wrong layer from a separation. 147
Trying for a while to remove the flask from the rotavapor still in vacuum conditions 143
Hose comes off of condensor (or out of sink) during the night and floods the lab. 132
Forgot to turn on vacuum before turning on rotavap motor, flask fell in bath and shattered 132
Ran multiple reactions in parallel, then proceeded to confuse the labels during parallel work-ups. 130
Forgot to disconnect vacuum hose before turning off water aspirator, tap water in reaction 122
After obtaining a good separation by TLC, you run a column only to find that your compound has decomposed on it. 120
Added a stir bar to a flask that was too large to remove. 115
Picked the "wrong" advisor 114
dropped reaction flask into silicone oil bath 105
Too lazy to record yield immediately after calulation and forgot after several hours. 101
Assumed some random bottle you found in the lab actually contained the chemical listed on the label. 97
Forgot to turn the nitrogen on into reaction,introduced air through septum. 95
Poured liquid into boiling reaction; contents erupted out of flask. 94
Waited for a long time for solvent to be rotavaped off but turned out forgot to turn the vacuum on when rotavaping solvent 94
Keeping the reagents/SM near to balance after using 91
Quenched the reaction without taking an NMR or a TLC to check conversion. Result: most of the precious starting material lost. 88
Forgot to put temperature probe in oil bath 88
Forgot to neutralize the reaction 80
Forgot to close off other reactions when using vacuum; results in dirty Schlenk lines. 74
Water introduced into an oil bath. Oil bath is heated above 100 degress. POP!! 74
Ran a gas-evolving reaction in a closed system. 69
forgot to turn off water suply 69
Added a stir bar to a flask sitting on a magnetic stir plate and the flask breaks. 67
Forgot that inside of drying oven door is hot, touched it, dropped glassware on floor. 65
Forgot to add the phenolphthalein before starting the titration. 63
Dropped a solvent bottle on the floor and it smashed 62
Broke multiple pipet tips in column while loading compound. 61
Contaminated compound with crap in the bump trap 59
Wore incorrect gloves, dissolved them. 56
forgot to add a catalyst 54
Plugged heating mantle directly into wall power. 54
Forgot to let the product cool to room temperature before sticking it in the ice bath. 54
Mix the fractions from a Chromatography and put the waste in the product. 51
lost vacuum on rotevap, flask drops, shattering into filthy water bath, extract organics from dirty water while filtering the dead bugs floating in it 50
Burned fingers while trying to pull spotting capillaries 46
dropped NMR tube with out the air on 45
Forgot to add starting material 41
Used boiling chips in a vacuum distillation. 40
Forgot to remove stirbar from reaction flask before pouring contents into separator funnel, which plugs stopcock and keeps solvent from draining out of separator funnel. 40
Dry ice trap on vacuum pump completely clogged with solid, didn't notice, kept turning up heat. 38
Set up reaction under Ar, added in reagents and forgot to add stir bar 36
Partially disintegrated a metal spatula in a strongly acidic reaction mixture 30
Condensed liquid oxygen or solid argon with liquid nitrogen. (A mistake you only make once.) 29
Filtered off the drying agent with a wrong type of funnel, resulting in the spillage of precious exctracts on the bench. 28
Used too much force opening a NMR tube and broke it (And cut yourself) 28
removing the vacuum in the rotary evaporator withot clip in the flask, this causes the loss of products 27
Dried Mg for Grigand open in a oven. 26
Did not show up to the lab for three months. 25
Trusted a fellow lab-mate's notebook without checking reference and watched as giant exotherm blew reaction everywhere. 21
Open both doors in air-lock chamber of glovebox 20
Acquired an NMR spectrum of the lock sample 20
forgot to make co spot in the TLC . 20
submitted NaCl crystals for x-ray analysis 16
After drying solvents with sodium, put water in the flask that still has sodium in it 15
Poured Stir-bar into Sep. Funnel, decided to shake it anyway and shattered the funnel. 15
Take 100ml 3-neck flask for 150 ml reaction mixture. 14
Add Pd/C catalyst to an ongoing hydrogenation without removing the H2 first: fire!! 12
After drying solvents with sodium, put water in the flask that still has sodium in it 12
didn't properly cool a bomb flask before opening, stuff shoots out everywhere 11
Tried to cool beer bottle quickly in liquid nitrogen, causing the bottle to shatter and beer to spray all over the laboratory. 11
Spent ~30 minutes troubleshooting the NMR because it wouldn't lock to CDCL3. Turned out I forgot to inject the sample. 11
Try to extract product using ethanol and water as the solvent system. The result being that your product is not extracted since ethanol and water are miscible. 11
Believed that LCMS data was real 11
Ran TLC without spotting plate. Didn't realize until visualization stage. 11
Burn hand on hot plate because it didn't look hot! 10
Made up NMR in TLC solvent (conveniently kept in old CDCl0 bottle) 9
Dump HCL down the drain and cost $$$ 9
Used short range pH paper when the long range pH paper was suppose to be used when acidifying solution. 9
Used too much toluene in a reaction and spent DAYS pumping it off 9
Mix the fractions after a distillation and put in the waste the product 8
believed that combinatorial chemistry and would revolutionize drug discovery 8
Turned oil bath up to max power. Left for the night. Advisor discovered the combusting oil bath early the next morning and calls you at home. 8
Started a practical session at 9am on a Monday morning (with standard lack of sleep & hangover) only to get a refreshing breath of HCl vapours. 8
Didn't check BH3 purity, or any other extremely moisture sensitive material, and recovered starting material. 8
Attached vacuum line to the distillation flask without properly securing the thermometer (breaking thermometer and flask thus). 7
Dump dry ice/acetone bath into sink, wait for maintenance to patch resulting crack. 7
Poured Stir-bar into Sep. Funnel, decided to shake it anyway and shattered the funnel 7
Good site! 7
Connected the Pipelines for the pump in the reverse direction during distillation, causes mercury thermometer to shoot out 6
Used oxygen instead of argon for an inert atmosphere 6
Brought in own air supply in an old bottle of tBuLi and started a fire in a drybox. 6
Didn't check for cracks on clips for rotavap. Flask drops in bath. 6
Dropped dry ice into a LiAlH4 reaction to "cool it down." 6
Turned up HCL(g) tank too much, hose bursts and recieved an acid spray to the face. 6
Drop a too small stopper into a column. Try to fish it out with a big pair of tweezers, drop it again and brake the column. 5
Try to extract product using acetonitrile and water as the solvent system. The result being that your product is not extracted since acetonitrile and water are miscible. 5
Play with the NMR magnetic field with a spatula while taking a scan. 5
Poured reaction into sep funnel with stopcock open..then trying to sop up reaction from benchtop with paper towels. 5
Mix two different samples in the same NMR tube ... 4
While washing glassware, combined saturated KOH/EtOH waste with concentrated HNO3 waste. 4
Dropped depth gauge down NMR spectrometer. 4
Accidentally mixed Sulphuric and Nitric acid with methanol whilst trying to "clean" a flask 4
Did not measure melting point of any organic compounds for an entire year. Measured melting point of all organic compounds synthesised within one year the night before thesis was due. 4
During a vacuum distillation of aniline, attached vacuum line directly to three-necked round bottom, thus bypassing the condenser. Suprised to see aniline condensing in the manifold. 3
Followed procedure as instructed by evil prof; should have seen the fountain of vile chromium-laced goo coming! 3
Didn't read the part of the instructions that said add concentrated sulfuric acid dropwise (read: SLOWLY). Had to leave lab for a few minutes while the acid cloud dispersed. 3
Degassed the teaction with methane instead of nitrogen 3
Mixed up the fridge and freezer, discovering product slush on your sealed broken flask the next day. 3
Spilled solvent into a drinking bottle on the benchtop then drank it 3
While performing the reflux reactions,Forgot to switch on the Water circulator. 3
Accidentally used adapter instead of stopper in sep funnel.... 2
Had the water bottle and mobile-phase bottle next to eachother on the bench while running a column. Guess which bottle I used when I next had to replenish the mobile phase. 2
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Added all five chemicals to create a reagent, forgot to add 400mL of water, then wondered how one could obtain four 40mL Spec 20 trials from 40.5mL of solution. 2
Wearing a Miami Dolphins or New England Patriots jersey on Football Sunday up here in sunny Upstate New York. Bonus demerits for wearing a Dallas Cowboys 1993 or 1994 Super Bowl Champions cap. 2
Degassed freshly distilled solvent with no outlet; septum flew off with satisfying 'pop.' 2
Blamed terrible gas on Swern reaction, which no one was performing at the time 2
Try to obtain a better vacuum by placing more cotton wool in the liquid nitrogen trap. 2
melted a round bottom flask while drying (under vacuum) celite for the glove box... twice. 2
finished unloading and realized you didnt wear any rubber, and now you are stuck with child support. 2
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During extraction, accidentally added soap solution instead of distilled water; two layers mysteriously hard to separate. 1
While 'maintaining' 2000 dollar high vacuum pump, pour oil into outlet. Express surprise that pump can hold so much oil. Supervisor not impressed :(. 1
Had to sneeze whilst handling sodium - covered my mouth - gloves on fire!! 1
Didn't believe post-doc when he said "KH is much more reactive than NaH"...sink fire 1
A chain was attached to a hood to secure a glass cylinder and you accdidently dissolved it 1
Added larger volume of gas to volatile reagent container than volume of solvent I was removing...too much positive pressure loss of volatile solvent on bench...no fire , luckily 1
Checking drybox gloves for leaks using vacuum, no leaks found but imploded faceplate of drybox 1
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Sliced Glovebox gloves because you were still wearing rings 1
finished unloading and realized you didnt wear any rubber, and now you are stuck with child support. 1
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