explain why the Magnesium Group cations are more likely to interfere with the Lithium Group tests than vice versa

Question

inorganic chemistry qualitative analysis

Answer 1

First off, cations from the Magnesium group—Mg, Ca, Ba, and Sr—are more reactive than cations from the Lithium group—Li, Na, K, and Rb. Secondly, magnesium-group cations form insoluble salts with anions (carbonate and phosphate, for example).

In general, elements from the magnesium groups typically form insoluble compounds with, for example, carbonate and phosphate anions rather than cations from the lithium groups when the qualitative analysis of the solution containing both metals (cations). Examples: MgCO3 (magnesium carbonate) and CaCO3 (calcium carbonate) are two water-insoluble salts contributing to the "hardness of water—the white solids that you can sometimes see in your sink.

On the other hand, salts generated between anions (carbonate and phosphate) and cations from the lithium groups are more soluble in water (qualitative analysis is carried out in water at various pH levels so the solubility heavily depends on the pH).