Marigold Chromatography

A class wants to test how solvent amount affects how far a marigold pigment travels on a chromatography strip.

Which variable is the independent variable?

To make a fair test when comparing 2 trials of marigold chromatography, which variables should be kept the same? (Select 2.)

Match each chromatography term to its best description.

In one trial, the pigment band traveled $3\text{ cm}$ from the start line. The solvent front traveled $6\text{ cm}$ from the start line.

Calculate the ratio $R_f = \frac{\text{pigment distance}}{\text{solvent front distance}}$.

Using $R_f = \frac{1}{2}$, convert $R_f$ to a percentage of the solvent front distance.

Percent mobility $= R_f \times 100%$.

Two chromatography trials produced these results:

• Trial A: $R_f = 0.40$

• Trial B: $R_f = 0.65$

Which trial shows greater pigment mobility (pigment traveled farther compared to the solvent front)?

If you change both the solvent amount and the time at the same time, it becomes difficult to tell which variable caused any change in $R_f$.

Graphing practice (draw on the canvas):

A group tested time as the independent variable and calculated percent mobility.

• 2 minutes: $30%$

• 4 minutes: $45%$

• 6 minutes: $60%$

Draw a bar graph with:

• a title

• labeled $x$-axis (Time in minutes)

• labeled $y$-axis (Percent mobility)

• bars at the correct heights

Write one controlled variable you would keep the same in all trials of this chromatography lab.