Which chemical is used to remove residual chlorine from bacteriological sample bottles?

Sodium thiosulfate is commonly used to dechlorinate water samples for bacteriological analysis. Chlorine in the water can inhibit the growth of bacteria in the samples, leading to inaccurate results during testing. Sodium thiosulfate reacts with free residual chlorine, neutralizing it effectively.

The way sodium thiosulfate works is that it provides sulfur that binds with chlorine, forming non-toxic and non-inhibitory products. This ensures that the microorganisms present in the sample can grow unhindered, allowing for accurate assessments of water quality regarding microbial contamination.

In contrast, other choices do not serve this purpose. Chlorine dioxide is typically used for disinfection rather than removal of residual chlorine, while potassium permanganate is also employed as a disinfectant and does not neutralize chlorine. Calcium hypochlorite is a source of chlorine used in water treatment and would not aid in the removal of residual chlorine in samples. Thus, sodium thiosulfate is the correct and effective choice for this specific application.