Suggest a compound that could serve as the stationary phase in this experiment.
Table 6.1 gives the $R_f$ values for different metal cations separated by TLC with water as the solvent. Identify the cation responsible for the spot at M in Fig. 6.1. Justify your answer.
The student carries out the experiment again using butan-1-ol as the solvent. In this experiment, the metal cations travel a smaller distance up the TLC plate. Suggest why the metal cations do not move as far up the TLC plate when butan-1-ol is used as the solvent.
The student sprays the TLC plate in Fig. 6.1 with $\text{KSCN(aq)}$. Some of the spot colours change because several of the metal cations undergo ligand exchange. Identify the ligands taking part in the ligand exchange reaction. ________ exchanges with ________.
In a third experiment, the pH of the metal-ion mixture is held constant by means of a buffer solution. The student makes the buffer by combining $20.0\,\text{cm}^3$ of $0.150\,\text{mol dm}^{-3}$ KOH(aq) with $50.0\,\text{cm}^3$ of $0.100\,\text{mol dm}^{-3}$ $\text{C}_8\text{H}_5\text{O}_4\text{K}$(aq). $\text{C}_8\text{H}_5\text{O}_4\text{K}$ is a weak carboxylic acid with $\text{p}K_a = 5.40$. Complete the equation for the reaction between $\text{C}_8\text{H}_5\text{O}_4\text{K}$(aq) and KOH(aq). $\text{C}_8\text{H}_5\text{O}_4\text{K}$ + .................................................
Calculate the pH of the buffer solution. Include all stages of your working.