How is Rf calculated?
Distance Spot Traveled/Distance Solvent Traveled
How is the purity of a reaction mixture determined using TLC?
It is determined by the spots (more than one spot = impure)
How is the identity of a product in a reaction mixture determined using TLC?
By comparing Rf values.
Given a set of TLC plates or Rf values, be able to determine reaction outcomes.
Compare the fraction to the fraction (or Rf) of the pure sample. If something produced no new products, and both the starting materials are still present, then the reaction will not proceed. When a reaction is finished, or runs to completion, that means t
IF F is a starting material and four syntheses were run, what does each plate indicate?
Different compounds within a mixture usually have different Rf values and hence will be seen as different spots. The number of spots in a given channel or lane are used to determine the number of different compounds in that mixture. If a lane has only one
Given two structures predict which will have a lower Rf.
More polar structure has lower Rf. (Stationary phase)
Less polar structure has higher Rf. (Mobile Phase) (When looking at a column, the one with dot on initial line has the highest polarity and the one that traveled farthest has lowest polarity).
Given 2 Rf's predict which compound is more polar.
The higher polarity the compound, the larger affinity of the compound to the stationary phase and the smaller the Rf. The lower the polarity the compound, the higher the affinity to the solvent and the larger the Rf. If a solvent is changed from a low pol
How are TLC and column chromatography similar and differ? (i. e. capillary vs. gravity used for separation)
In TLC the stationary phase is a thin layer of silica or alumina spread on an inert support, usually a plastic sheet or a glass plate. The mobile phase moves upward by capillary action.
In column chromatography a glass or plastic tube is filled with the p
What are the various layers in column chromatography and explain their purpose? Why were the solvents introduced into the column in a particular order?
In the column chromatography apparatus, the top layer of sand prevents the solvent (mobile phase) from disturbing the adsorbent (which is the stationary phase) when it's poured in.
The bottom layer of sand provides a level surface to keep the adsorbent la
What concept or process allow for separation in column chromatography? ( Hint: review all note dealing with separation)
Partitioning, separation, based on affinity between mobile phase and stationary phase.
When separating two or more compounds via chromatography, it is very important to choose the correct solvent as a mobile phase.
If too weak of an eluting power solvent
What is a mobile phase? Give an example
Mobile phase is a medium used in chromatography which moves through the stationary phase. In TLC and column chromatography, the mobile phase is an organic liquid. In Gas Chromatography (GC) the mobile phase is a gas.
Is TLC used to analyze small or large samples?
Small
Is Column Chromatography used to analyze small or large samples?
Large
What is the relationship between eluting power and polarity?
In general the stronger the eluting power the more polar the solvent.
Rank the eluting power of: ethers, esters, ketones, alcohols, acids, hydrocarbons, and halogenated hydrocarbons.
hydrocarbons<halogenated hydrocarbons<ethers<esters<ketones <alcohols<acids
Rank the eluting power of: heptane, toluene, MTBE, methylene chloride, acetic acid, acetone, ethanol, and ethyl acetate.
heptane<toluene<methylene chloride<MTBE
<ethyl acetate<acetone<ethanol<acetic acid
What stationary phase did we use?
Alumina
What would happen if a solvent is changed from a low polarity to a high polarity?
The eluting power will increase and all the Rf values will increase.
What are some pitfalls of TLC?
If you use too much solvent in the bottom of the beaker, or if you carry the beaker around during the experiment allowing the solvent to slosh part way up the plate, the sample you are studying may wash off the plate into the solvent at the bottom.
If you
What is the most common mistake made during column chromatography? What does it lead to?
If any part of the stationary phase is allowed to run dry. This will lead to the column support cracking and will result in poor separation or incomplete elution of the components.
What are the hazards of ferrocene?
Causes irritation to the eyes and skin.
Prolonged ingestion or inhalation may cause liver damage.
What are the hazards of acetylferrocene?
Is toxic if ingested or absorbed through skin.
What are the hazards of Dichloromethane (Methylene chloride)?
High level exposure to dichloromethane can cause central nervous system depression; long term exposure may cause tumors.
What kind of substance is methylene chloride?
Chlorinated organic material
What are the hazards of Heptane, ethyl acetate and methyl t-butyl ether (MTBE)?
They are flammable organic liquids.
Describe eluting power.
The ability of a solvent (mobile) phase to transport compounds with it through the stationary phase.