Question

1. A mixture containing Compound X and Compound Y is analyzed using silica gel TLC. a. If Compound X has an Rf value of 0.7 and Compound Y has an Rvalue of 0.3, which compound is more polar? Explain. b. The solvent traveled 50 mm. How far did Compound Y travel? 2. Why isn't it reasonable for an R. value to be greater than 1? 3. How many spots would you expect to see if you conducted a TLC separation of Excedrin? Explain. 4. Why would a different solvent produce different R values for the same compound?

Answer 1

1a. in chromatography there are two phases -one is stationary phase which is fixed and other is mobile phase which is not fixed if the compound have more adhesive force between the stationary phase and itself it will stick with the stationary phase and will move slowly and the compound is more polar because  the adsorptivity of compounds increases with increased polarity (  more polar the compound is   stronger it binds to the adsorbent(stationary phase and less is the R_f) Non-polar compounds move up the plate most rapidly (higher R_f value), whereas polar substances travel up the TLC plate slowly lower R_f value).

compound X = R_f =0.7

compound y = R_f =0.3

compound X = R_f =0.7>compound y = R_f =0.3

so compound X is non polar and compound Y is polar

b) R_f = ( distance travelled by the compound Y)/( distance travelled by the solvent)

( distance travelled by the solvent) =50 mm

distance travelled by the compound Y =R_f * distance travelled by the solvent

distance travelled by the compound Y =0.3*50mm =15mm.