Sodium thiosulfate is neither an acid nor a base; it is considered a neutral salt. It is derived from the reaction of sulfurous acid and sodium hydroxide, which can lead to some confusion about its classification. In an aqueous solution, sodium thiosulfate does not significantly alter the pH, thus behaving neutrally.
The compound is often used in various applications, including photography, water treatment, and as an antidote in certain poisoning cases. Its pH can vary depending on the concentration and specific conditions, but typically, it remains close to neutral on the pH scale. Therefore, it is accurate to categorize sodium thiosulfate as a neutral substance rather than strictly an acid or a base.