Final answer:
In the treatment of clients with pemphigus, complexing agents such as pyrophosphate or triphosphate may be added to bath water to bind with magnesium ions and prevent irritation from hard water.
Step-by-step explanation:
The chemical that is often added to the bath water of a client with pemphigus is a type of complexing agent, which could include compounds such as pyrophosphate (O3POPO34, or P₂O₇⁴) or triphosphate (P30105³).
These agents act by chelating or binding Mg²+ ions that are abundant in hard water, thus preventing the precipitation of magnesium and calcium salts which could irritate the skin. While this does not directly treat pemphigus, it can help prevent additional skin irritation during bathing.