Question

A colorless lead salt, when heated, produces a yellow residue and brown fumes. Name the brown fumes.

Answer 1

Hint:To answer this reaction, you must recall the salts of lead and their properties. By looking at the various possible anions possible in a lead salt, find which of the following would form a precipitate and brown colored fumes. Reactions like these in which two or more than two products are formed from a single reactant are known as decomposition reactions. The compound formed consists of nitrogen and oxygen.

Complete answer:
Lead produces a number of compounds and also a number of insoluble salts. Some common insoluble salts of lead are lead hydroxide which is a white colored precipitate, lead chloride which is a white colored precipitate, lead iodide which is a yellow colored precipitate and lead oxide which too is a yellow coloured precipitate.
If the residue is taken to be lead iodide, there is no explanation for the formation of the brown fumes. Brown fumes are generally obtained when nitrogen dioxide gas is released. Assuming the brown vapours to be those of nitrogen dioxide, the initial salt must be lead nitrate which is a colorless salt. Considering this to be the case, the residue obtained on heating would be that of lead oxide which is a yellow colored salt.
Thus, the brown fumes are those of Nitrogen dioxide.

Note:
A decomposition reaction is the reaction which involves the breaking of a chemical compound by the action of heat, light or electrical energy to give two or more new substances. A decomposition reaction caused when heat is provided to the compound is known as thermal decomposition reaction.