Question

Metals used in preparation of dihydrogen in lab

Hint:

Always specify "granulated" zinc rather than just "zinc", as the granular form provides a larger surface area and its inherent impurities facilitate a steady, manageable rate of hydrogen evolution.

Answer 1

Step 1: Understanding the Concept:
In the laboratory, dihydrogen (\( \text{H}_2 \)) gas is typically prepared by reacting an active metal with a dilute mineral acid or an aqueous alkali.
Step 2: Key Formula or Approach:
The approach is to identify the standard metal utilized in school and research laboratories for safely and efficiently generating hydrogen gas.
Step 3: Detailed Explanation:
The most common and standard method for preparing dihydrogen in the laboratory involves the reaction of granulated zinc with dilute hydrochloric acid (\( \text{HCl} \)) or dilute sulfuric acid (\( \text{H}_2\text{SO}_4 \)).
The chemical reaction is:
\[ \text{Zn}_{(s)} + 2\text{H}^+_{(aq)} \rightarrow \text{Zn}^{2+}_{(aq)} + \text{H}_{2(g)} \] Granulated zinc is preferred over pure block zinc because the impurities present in it act as a local catalyst (forming micro-galvanic cells) which speeds up the reaction.
Alternatively, zinc can also react with aqueous alkali (like NaOH) to produce hydrogen and sodium zincate, though acid is more commonly used.
Highly reactive metals like Sodium or Potassium are not used in the lab because their reaction with acids or water is violently explosive.
Step 4: Final Answer:
Granulated Zinc is the metal used.