When yellow phosphorus (P₄) reacts with chlorine gas (Cl₂), it forms phosphorus trichloride (PCl₃) or phosphorus pentachloride (PCl₅), depending on the conditions of the reaction (e.g., temperature and pressure). The initial reaction can be represented as follows:
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Formation of Phosphorus Trichloride: \[ P_4 + 6Cl_2 \rightarrow 4PCl_3 \]
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Formation of Phosphorus Pentachloride: \[ P_4 + 10Cl_2 \rightarrow 4PCl_5 \]
The yellow liquid that you mention is likely phosphorus trichloride, which is a yellowish liquid at room temperature.
When this yellow liquid is exposed to air, it fumes because phosphorus trichloride is highly reactive with moisture and can react with water vapor in the air to produce hydrochloric acid (HCl) and phosphorus oxides (P₂O₅):
\[ PCl_3 + H_2O \rightarrow HCl + HPO_3 \]
The presence of HCl gas in the vicinity can create visible white fumes, which are due to the formation of hydrochloric acid when the vapor interacts with moisture in the air. This reaction explains both the fuming behavior and the corrosive nature of the vapors released when the yellow liquid is exposed to air.
To summarize:
- Yellow phosphorus reacts with chlorine gas to form phosphorus trichloride (or pentachloride), resulting in a yellow liquid.
- The yellow liquid fumes when exposed to air due to its reaction with water vapor, producing hydrochloric acid and phosphorus oxides, leading to visible fumes.
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