Final answer:
Adding sodium carbonate to the residual NaHS to mitigate hydrogen sulfide emissions is an effective approach. The reaction of sodium carbonate with hydrogen sulfide produces sodium sulfide, water, and carbon dioxide, helping to reduce hazardous off-gassing.
Step-by-step explanation:
The question deals with the mitigation of hazardous H2S gas generated from the decomposition of an expired NaHS solution. If the pH of the NaHS solution has decreased, it would indeed contribute to the release of more H2S gas, which is potentially very dangerous as it can reach immediately dangerous to life or health (IDLH) conditions.
Adding solid sodium carbonate to the solid NaHS in the tank could help neutralize the remaining acid, thus reducing the generation of H2S.
The sodium carbonate (Na2CO3) would react with any hydrogen sulfide (H2S) present to produce water (H2O), carbon dioxide (CO2), and sodium sulfide (Na2S), which is less volatile and therefore reduces the risk of off-gassing:
Na2CO3(s) + 2H2S(g) → 2Na2S(s) + CO2(g) + H2O(l)
This reaction should not pose any adverse effects if managed properly, with the correct stoichiometric proportions, under controlled conditions, and with adherence to safety protocols.