Flashcards in Lab Final Deck (157)
2 methods to determine organic versus aqueous layer in solution
1. add a drop of water. If water mixes with top layer, it is aqueous. If water falls to bottom layer, bottom layer is aqueous
2. predict based on density. If organic solvent contains heavy atoms, like Cl, it will be on bottom. If organic solvent isnt heavy (like hexane or ethers), it will be on top
just a general carboxylic acid
What does the separatory funnel allow chemists to do?
Easily see the barrier between two layers and then seperate them using a stopcock
What does a liquid-liquid extraction require?
Two liquids that are immiscible (like oil and water)
What layer do charged compounds or ionic compounds go in?
Often charged molecules are polar so they go in polar aqueous layer
What layer do uncharged organic compounds or non-ionic compounds go in?
Typically non-polar so they go in organic layer
How does extraction work?
Add an organic solvent and mix, then the desired compound (in our case dye) will move to aqueous or organic layer, then can use the separatory funnel to separate one layer from the other and isolate the desired compound
What is important when picking a solvent for extraction?
1) Will dissolve the solute of interest
2) Is immiscible to the aqueous layer (often water)
How should the separatory funnel be supported?
With a ring stand NOT a clamp
What must you do prior to separating the layer?
Extract the gas from the funnel
and then remove the stopper from the top of the funnel
Difference between washing and extraction?
Extraction moves the desired compound by placing it in the organic solvent
Washing keeps the desired compound in the starting layer
The ratio of concentrations of a compound in a mixture of two immiscible phases at equilibrium
Partition coefficient equation
P= (solubility of compound in organic layer)/(solubility of compound in aqueous layer)
What can you use to determine how many grams of desired compound is removed by the organic layer/aqueous?
System of equations and partition coefficient
Caffeine is wildly soluble in ethanol. Could you have used ethanol in- stead of dichloromethane to extract the caffeine from tea? Why or why not?
Ethanol is soluble in water and you would not be able to have two distinct layers to separate
What does TLC stand for?
Thin layer chromatography
What are some uses of TLC?
to see if a reaction has gone to completion
help identify final product
What do you need in order to be able to use TLC as an identification tool?
A known TLC of the sample to compare
How fast do polar substances elute in tlc?
Polar substances are more strongly attracted to the stationary phase (silica gel) and therefore elute more slowly
How fast do non-polar substances elute in tlc?
Non-polar or less polar substances are less attracted to the stationary phase (silica gel) and therefore elute more rapidly
Why use TLC compared to other methods of anaylsis?
low cost, quick analysis time, convient, and simple
How should you prepare the compound for analysis in TLC?
Solvent should dissolve the compound well and evaporate quickly
Often use dichloromethane
How does the solvent move up plate in TLC?
How far the solvent traveled in TLC
Rf= (distance traveled by compound)/(distance traveled by solvent front)
What is an advantage to 1-pot synthesis?
do not need to isolate intermediates at each step
can mix altogether
What is a disadvantage to 1-pot synthesis?
you can have more impurities in your final solution
How can you tell if 1-pot synthesis is working?
Color changes throughout the experiment is one way
What are the three compounds present in TLC?
1) Stationary phase
2) Mobile phase (the solvent)
3) The analyte (what you are studying)