Final answer:
The formula for phosphorous trichloride is PCl₃. It is a colorless liquid formed by the reaction of chlorine gas with molten phosphorus and can be hydrolyzed to produce phosphorous acid and hydrogen chloride.
Step-by-step explanation:
The formula for phosphorous trichloride is PCl₃. This is confirmed by the description indicating that phosphorous trichloride is prepared by passing chlorine gas over molten phosphorus, which leads to the formation of PCl₃. Phosphorous trichloride is also involved in reactions to form phosphorous acid through hydrolysis, as shown in the chemical equation: PCl₃ (l) + 3H₂O(l) → H₃PO₃(aq) + 3HCl(g).
When considering the molecular structures found in Figure 18.41, we can notice that phosphorus pentachloride and phosphorous trichloride are both important halides of phosphorus, with the former having the formula PCl₅ and the latter PCl₃. These molecular structures respond to water differently, with phosphorous trichloride yielding phosphorous acid and phosphorus pentachloride yielding phosphoric acid.