Question

High purity $(>9995 \%)$ dihydrogen is obtained by

• A. reaction of zinc with aqueous alkali.
• B. electrolysis of acidified water using platinum electrodes.
• C. electrolysis of warm aqueous barium hydroxide solution between nickel electrodes.
• D. reaction of zinc with dilute acid.

Answer 1

The Correct Option is C

To determine the method by which high purity dihydrogen, greater than 99.95%, is obtained, let's evaluate the given options based on the chemistry principles involved:    

1. Reaction of zinc with aqueous alkali: This method typically results in the formation of hydrogen gas, but the purity isn't particularly high due to impurities from zinc and other reaction by-products. Therefore, this method doesn't yield high purity dihydrogen.
2. Electrolysis of acidified water using platinum electrodes: While electrolysis of water can produce hydrogen, the process depends on the purification of water and electrodes. Nevertheless, it generally does not reach purity levels over 99.95% without specific purification steps. Additionally, this method is more commonly associated with laboratory preparation than high industrial purity.
3. Electrolysis of warm aqueous barium hydroxide solution between nickel electrodes: This is a recognized method to obtain high-purity dihydrogen gas. The process minimizes contamination because nickel and barium hydroxide in aqueous solution do not introduce significant impurities. Thus, this method can successfully produce dihydrogen with purity exceeding 99.95%.
4. Reaction of zinc with dilute acid: Similar to the alkaline reaction with zinc, this method also produces hydrogen gas but with a number of impurities. The dilute acid can introduce various contaminants, so it does not achieve such a high level of purity.

Thus, the correct answer is the electrolysis of warm aqueous barium hydroxide solution between nickel electrodes, as it specifically facilitates the production of high purity dihydrogen (greater than 99.95%).

This method is effective due to its ability to limit contamination, ensuring that the resulting dihydrogen gas meets the high-purity criteria needed for specialized applications.