Plant Chromatography & Pigment Analysis

In paper chromatography, the stationary phase (cellulose) is polar. If a pigment has a very low Rf value, what does this suggest about its chemical nature?

• The pigment is highly polar and has a strong affinity for the stationary phase.

• The pigment is non-polar and prefers the mobile phase.

• The pigment is too small to be carried by the solvent.

• The pigment has reacted chemically with the solvent front.

Why does Beta-Carotene usually travel the furthest in a chromatography run using a non-polar solvent?

• It is the largest molecule and pushes other pigments aside.

• It forms hydrogen bonds with the cellulose paper.

• It is a hydrocarbon with no polar groups, making it highly soluble in the solvent.

• It is heavier than chlorophyll, giving it more momentum.

If you move from Paper Chromatography to Silica TLC, and the silica is more polar than the paper, what happens to the Rf of polar pigments?

• The Rf value will likely increase.

• The Rf value will likely decrease.

• The Rf value will remain exactly the same.

• The Rf value will become greater than 1.0.

Which of the following describes the "Sieve Effect" in chromatography?

• Smaller molecules get trapped in the pores and move slower.

• Only green pigments can pass through the paper fibers.

• The solvent "filters" out the colors based on their brightness.

• Larger molecules encounter more physical resistance moving through the fiber matrix.

• The experiment failed because the results are not different.

• The two plants contain the same chemical pigment.

• Grass is biologically identical to spinach.

• The solvent was contaminated with yellow dye.

Why is it important to mark the baseline with a pencil rather than a pen?

• Pencil lead is polar and helps the pigments move.

• Pen ink is soluble and would separate along with the plant pigments.

• Pen ink reacts chemically with the spinach chlorophyll.

• The solvent cannot pass over pen ink.

Chlorophyll a is larger than Beta-Carotene. If polarity were equal, which would move slower due to size alone?

• Chlorophyll a

• Beta-Carotene

• They would move at the same speed.

• Neither, as size has no effect on chromatography.

What is the primary purpose of keeping the chromatography chamber sealed with a lid?

• To keep oxygen out so the pigments don't change color.

• To increase the pressure and force the solvent up faster.

• To saturate the air with solvent vapor and prevent the paper from drying out.

• To prevent the teacher from smelling the chemicals.

• 1.54

• 6.5

• 0.35

• 0.65

If you used a more polar solvent (like ethanol) instead of a non-polar one, what would you expect to happen to the Rf values of the polar pigments?

• The Rf values would decrease.

• The Rf values would increase.

• The pigments would stop moving entirely.

• The Rf values would stay the same because the paper is still polar.