Which chemical is commonly used to dechlorinate water for bacteriological samples?

Sodium thiosulfate is commonly used to dechlorinate water for bacteriological samples because it effectively neutralizes free chlorine and chloramines, which can be harmful to microorganisms present in those samples. Chlorine is typically used in water treatment processes to disinfect water by killing bacteria and pathogens. However, when collecting samples for bacteriological analysis, the presence of residual chlorine can inhibit the growth of bacteria, leading to inaccurate results.

Using sodium thiosulfate in the sample can ensure that any residual chlorine is effectively neutralized, allowing for a more accurate assessment of the microbial content. This chemical reacts quickly with chlorine, making it a reliable choice for dechlorination in laboratory settings.

The other chemicals listed do not serve the same purpose in the context of dechlorination. Hydrochloric acid, for example, is primarily used to adjust pH levels, while potassium permanganate is an oxidizing agent that could potentially harm microbial life rather than support accurate testing. Calcium carbonate is mainly employed to buffer water alkalinity and would not effectively neutralize chlorine.