Question

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Post-Lab Questions 1. Does a large value for Rf mean that the solute has a relatively strong affinity for the solvent (mobile phase) or a relatively weak affinity for the solvent? 2. Briefly describe what experimental conditions gave you the best separation. 3. The structure of indigo is shown in the discussion section. This type of structure is common for organic molecules and not all atoms, lone pairs and bonds are shown. Use your textbook as mentioned earlier in the discussion (or on-line) and decipher this structure and answer the questions below: a. How many total lone pairs are in the indigo molecule? b. How many o bonds and how many it bonds are in the indigo molecule ? c. Would you expect that the indigo molecule is highly water-soluble? Explain in the space below. 8:05 PM 3/29/2020 о ні де ба Type here to search Prison presence End Home s ous to Home Pgup B End Tippgup me pegar G

Answer 1

Rf value and its affinity to the solvent

Rf value is the distance travelled by the given compound divided by the distance travelled by the solvent front.

Rf value, Rf = 0 indicate that the compound does not migrate in that system. It does not have affinity to the solvent.

Rf=1 means that the compound has no binding with the sorbent. It does have high affinity to the solvent.

Experimental Conditions for best separation

i. Temperature

ii. Solvent concentration and purity

iii. Amount of sample spotted on Chromatography medium

iv. Polarity of the solvent

v. A solvent which has a stronger interaction for a particular chemical will more easily overcome any affinity of the chemical for the absorbent layer, and move that chemical farther in a given period of time

Structure of Indigo

All bonds between atoms in most organic compounds contain one sigma bond each. If it is a single bond, it contains only sigma bond. Multiple bonds (double and triple), however, contains sigma and pi bonds. Double bonds have one each, and triple bonds have one sigma bond and two pi bonds.

Ø Indigo has two lone pairs

Ø Indigo has 9 Pi Bonds and 25 sigma bonds

Ø Indigo is an inorganic compound and non-polar substance and consequently, insoluble in water.