Term
| what is the most critical factor in determining accurate melting point? |
|
Definition
|
|
Term
| how fast should heat be increased for accurate melting point |
|
Definition
|
|
Term
| why was the glass funnel heated prior to filtration during recrystalization lag |
|
Definition
| to prevent premature crystalization |
|
|
Term
| list 3 ways to induce crystalization |
|
Definition
| seeding, scratching, flash freezing |
|
|
Term
| when running a TLC of napthalene, butyric acid and phenyl acetate, what order (from top to bottom) would you find them in? |
|
Definition
top = napthalene
middle = phenyl acetate
bottom = butyric acid
(less polar travels farther) |
|
|
Term
| why must TLC be run in a closed container with interior vapor saturated with solvent? |
|
Definition
| to prevent the solvent from evaporating from the TLC plate |
|
|
Term
| a more polar solvent in TLC will do what to an Rf value |
|
Definition
| more polar solvent means compound travels farther so larger Rf value |
|
|
Term
| if a compound is run on a 3inch plate and has an Rf value of .8, what would the Rf value be if the same compound was run on a new plate that is 6 inches long with the same solvent? |
|
Definition
| Rf value says the same - its a ration of solvent line to compound not a measurment of distance traveled. |
|
|
Term
| in the dehydration of alcohols to to alkenes, what is the role of phosphoric acid? |
|
Definition
| it protonates the alcohol into a good leaving group. (HINT: if you see an acid theres a pretty good chance its protonating something the opposite is true for bases - they likely deprotonate something) |
|
|
Term
| what is the function of a chaser solvent? |
|
Definition
| to "rinse" or "chase" the desired product out of the fractionating column |
|
|
Term
| give 2 reasons that water is added during the preparation of aspirin: |
|
Definition
1) to induce crystallization of product
2) hydrolyze acetic anhydride to 2 acetic acid |
|
|
Term
| why must grinard reagent have very dry glasswear |
|
Definition
| its a really strong base so any source of protons will have acid base reaction and inactivate it. |
|
|
Term
| draw structure of ortho-vanillin |
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
|
Definition
|
|
Term
| what would be the effect of incomplete drying of a sample on melting point |
|
Definition
| melting point would be depressed and broadened (think impurity) |
|
|
Term
| why should you use the minimum amount of solvent for crystalization |
|
Definition
| to obtain maximum product yeild (some product would remain dissolved in the solvent when attempting to crystalize thereby lowering your yeild) |
|
|
Term
| during the extraction lab, you checked the Ph of the solution. What was the purpose of doing this? |
|
Definition
| to ensure all the product was reprotonated to its original form. If the solution is acidic, that mean there are free H+ ions, if there are free H+ ions then all the salt has been reprotonated. (since any H+ would react with the salt if any salt was still present) |
|
|
Term
| list 3 precautions when spotting a TLC plate (note I have listed the three I used, there are other acceptable aswers - refer to your exam if unsure about your answer) |
|
Definition
Spots should not be too close together/touching
spots must not be too concentrated (will 'drag' or too dilute
should avoid touching TLC plate with fingers since oils could skew results |
|
|
Term
| the piece of glassware that distillate flows into from the condenser is called what? |
|
Definition
| collecting vessel/filtrate flask |
|
|
Term
| why cant we use a water hexane mixture in recrystalization |
|
Definition
| those solvent are immiscible and recrystalization solvent pares must be miscible |
|
|
Term
| what is the effect of reducing atmospheric pressure on boiling point? If substance A and B can be separated by distillation at 1 atm, can they be separated at .5atm? |
|
Definition
| the boiling point lowers proportionally to the pressure so substance A and B will still be separable - but the boiling point for BOTH will be lower |
|
|
Term
| aqueous carboxylic acid can be separated from phenol using sodium bicarb. What chemical property makes the separation possible? |
|
Definition
| acidity - one is a strong acid one is a weak acid. Sodium Bicarb (a week base) will only react with the strong acid forming a salt that can be separated |
|
|
Term
| what is a practical advantage of Dichloromethane (density = 1.325g/mL) over ether (densidy = .75g/mL) |
|
Definition
| dichloromethane is more dense then water (remember D=1g/ml) and will form the organic layer on the bottom of the separatory funnel. This layer can then be drawn off through stopcock. |
|
|
Term
| two substances follow the solvent line in a TLC plate and both end up with a Rf of 1. Does this mean they are identicle? What further expiraments do you feel should be conducted (if any) |
|
Definition
This plate is inconclusive. Another TLC plate should be run with a less polar solvent. Additionally, a melting point could be obtained for A and B and then also a mixture of the two (if not identical, the melting point should become depressed).
NOTE - beshir wants the second TLC plate as the answer so make sure thats included - he might also change this question so the substances have Rf of 0 in which case the same answer except use a more polar solvent |
|
|
Term
| Under what cirumstances do mixed solvents find application for recrystalization (really beshir? why not just ask when would you need to use mixed solvents lol) |
|
Definition
| when there is no one solvent capable of dissolving the product and impurity completely at high temp but only dissolving the impurity at low temp (so if the solvent isnt capable of dissolving only impurity at low temp). A mixed solvent system would dissolve everything at high temp then the second solvent would reduce solubility to the product causing only it to "crash out" |
|
|
Term
| during final stages of extraction, the ether layer is often cloudy. Anhydrous CaCl2 is added and the solution becomes clear. Explain what caused the clearing |
|
Definition
| Water in the ether layer causes the cloudiness. Anhydrous CaCl2 'absorbs' or reacts with the water removing it from the ether solution causing it to become clear. |
|
|
Term
| A hot saturated solution of material is passed through a fluted peice of funnel paper in a long step funnel. Name 2 things wrong with that procedure. |
|
Definition
1 - the funnel should not be a long stem funnel - it should be the stemless funnel (NOTE this is not the bruchner funnel)
2- the funnel should be heated up prior to filtering to prevent premature crystalization and product loss |
|
|
Term
| a slightly polar organic compound has a K value of 4 (in favor of ether) what is one simple way to increase the partition coefficient? |
|
Definition
| addition of saturated NaCl to the aqueous layer will make the layer more polar forcing the organic compound further into the ether layer. |
|
|
Term
| to extract mixture of a base, an acid and a nuetral compound, what reagent would be added first? What does the reagent do? |
|
Definition
NaOH (a strong base) will react with the acid and deprotonate it forming a salt that moved into the aqueous layer.
NOTE- if there was a strong acid, weak acid and neutral compound, you would use sodium bicarb. |
|
|
Term
what is this point called
[image] |
|
Definition
|
|
