1.1. Chlorine reacts with phosphorus to form phosphorus trichloride.

Draw a diagram showing the arrangement of the outer electrons in one molecule of the covalent compound, phosphorus trichloride.

Use x to represent an electron from a phosphorus atom.
Use o to represent an electron from a chlorine atom.

1.2. Extended Only

Phosphorus trichloride reacts with water to form two acids.

i) Balance the equation for this reaction.

PCl₃ + .......H₂O → .......HCl + H₃PO₃

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ii) Describe how you could show that phosphorus acid, H₃PO₃, is a weaker acid than hydrochloric acid.

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iii) Two salts of phosphorus acid are its sodium salt, which is soluble in water, and its calcium salt which is insoluble in water. Suggest a method of preparation for each of these salts from aqueous phosphorus acid. Specify any other reagent needed and briefly outline the method.

Sodium salt

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   Calcium salt

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