Question

Pre-Lab Questions from lab Paper Chromatography of a Metal Cation Mixture

1. How are each of the cations, Fe3+, Ni2+ and Cu2+, visualized on the paper?

2. In the procedure below, you are specifically directed to identify each original spot using a penciled mark. Why do you suppose an ink pen cannot be used for this purpose?

3. Suppose Zn2+ where also a cation in the mixture. And further suppose the resulting chromatogram shows a spot corresponding to this cation at 2.7cm from its origin. If the solvent traveled 8.8cm from the same origin, what is the Rf value for Zn2+?

Answer 1

Fe³⁺ , Ni²⁺ and Cu²⁺ will be visualised as rust colored, strawberry red and deep blue respectively.

Fe³⁺ + 3OH^-   Fe(OH)₃   rust colored

Ni⁺² +2 NH₃ + 2 Dimethyglyoxime Ni(DMG)₂ (strawberry red) + 2 NH₄⁺

Cu²⁺ + 4NH₃ [Cu(NH₃)₄]^-2 Deep blue cored

2. we cannot use a pen to identify the colored spot because in the ink of a pen all the three ions Fe³⁺, Ni²⁺,Cu²⁺ are already present. It will adversly effect the experiment.

3.

Rf value of Zn²⁺ = distance travelled by ion distance travelled by the solvent

= 2.7 8.8 = 0.306