Question

1. how could you separate tellurium dioxide, teo₂, from sio₂?
2. how could you separate lauric acid from α -naphthol? (see table 2.1.)

Explanation:

1. Tellurium dioxide ($TeO_2$) is amphoteric and can react with strong bases while silica ($SiO_2$) is acidic and has different reactivity patterns. One could use a strong - base solution like sodium hydroxide ($NaOH$). $TeO_2$ will dissolve in the base forming a soluble tellurite salt while $SiO_2$ will remain insoluble and can be filtered off. Then, by adjusting the pH of the solution containing the tellurite salt, $TeO_2$ can be precipitated out.
2. Lauric acid is a carboxylic acid and $\alpha$-naphthol is a phenol. Carboxylic acids react with sodium bicarbonate ($NaHCO_3$) to form water - soluble carboxylate salts while phenols do not react with $NaHCO_3$. So, treating the mixture with $NaHCO_3$ solution will dissolve lauric acid as its carboxylate salt. The $\alpha$-naphthol can be separated by filtration. Then, by adding a strong acid like hydrochloric acid ($HCl$) to the solution containing the lauric - acid carboxylate salt, lauric acid can be precipitated out.

Answer:

1. Use a strong - base solution (e.g., $NaOH$) to dissolve $TeO_2$, filter off $SiO_2$, and then precipitate $TeO_2$ by adjusting pH.
2. Treat the mixture with $NaHCO_3$ solution, filter off $\alpha$-naphthol, and then precipitate lauric acid by adding a strong acid.