Preparation of Dihydrogen — Prelims Strategy

Prelims Strategy

To excel in NEET questions on dihydrogen preparation, a systematic approach is essential. Firstly, memorize the key reactions, reagents, and conditions for both laboratory and industrial methods. For lab preparations, focus on active metals (Zn, Mg, Fe) with dilute non-oxidizing acids (HCl, $H_2SO_4$) and amphoteric metals (Zn, Al) with strong alkalis (NaOH, KOH).

Understand why highly reactive metals (Na, K) and oxidizing acids ($HNO_3$) are avoided. For industrial methods, prioritize steam reforming of methane ($CH_4 + H_2O \xrightarrow{Ni, 1000^circ C} CO + 3H_2$), the water-gas shift reaction ($CO + H_2O \xrightarrow{Fe_2O_3/Cr_2O_3} CO_2 + H_2$), and electrolysis of water/brine.

Secondly, understand the underlying chemical principles, especially redox reactions. Be able to identify which species is oxidized and which is reduced. Thirdly, pay attention to by-products and purification steps.

For instance, know that $CO_2$ is removed after the water-gas shift reaction and how it's done. Fourthly, practice identifying the most suitable method for a given scenario (e.g., 'which method yields the purest hydrogen?

' or 'which is the most economical industrial method?'). Finally, solve previous year's questions to familiarize yourself with the common question patterns and potential trap options. For conceptual questions, carefully read all options and eliminate incorrect ones based on your understanding of reactivity and reaction conditions.