Lab 2 - Cation Exchange with Sphagnum Moss

Question 1

sphagnum moss

Answer 1

cell walls contain carboxyl groups that are negatively charged, act as a solid phase during chromatography

Question 2

variables

Answer 2

independent: concentration of potassium, pH, charge
dependent: elution time

Question 3

rate of elution

Answer 3

as pH decreases, the concentration of H+ ions increases, and the elution rate increases

as the concentration of potassium increases, the rate of elution increases

Question 4

test reagents

Answer 4

Nessler’s reagent, NH4+ = orange-brown

sodium hypochlorite, Mn2+ = blackish-brown

potassium thiocyanate, Fe3+ = red

Question 5

Why did you test positive and negative controls?

Answer 5

To validate the procedure.

Question 6

Why did we expect the ions in solution A to elute in a certain order?

Answer 6

NH4+, Mn2+, Fe3+ –> The greater the charge of the cation, the greater the strength of the bond.

Question 7

Did you test high KCl or low pH? If everything had worked as expected, what would your solution B or C test plate have looked like?

Answer 7

High KCl. Faster and more pronounced color change because we increased weakest cation which elutes faster.

Question 8

What would your solution A test plate have looked like if Sphagnum moss was packed too loosely?

Answer 8

Would be darker because cations would get through easier –> greater and faster color change

Question 9

We expected the low pH solution to speed up the elution of the ions through the column. We never tested a high pH solution. Why is it that a high pH solution could not be expected to speed up the elution of the ions through the column?

Answer 9

More H+ bonds to outcompete –> the K+ binds to the charged carboxyls so the other ions don’t pass through faster