Explain:

(a) The use of lead pipes for drinking water supply is being discontinued.

(b) Chalk hills dissolve in rain water.

(c) Hard water is unfit for boilers.

(d) Iron chloride forms a saturated solution when exposed to the atmosphere.

(e) A bottle containing concentrated H₂SO₄ should be stoppered.

(a) Lead is toxic. When water flows through lead pipes, especially soft or acidic water, it can dissolve lead ions into the water. Ingesting lead causes serious health issues, especially in children (like brain and kidney damage).

(b) Chalk is mainly calcium carbonate (CaCO₃). Rainwater absorbs carbon dioxide (CO₂) from the air and forms carbonic acid (H₂CO₃), a weak acid:

CO₂ + H₂O ⟶ H₂CO₃

This reacts with calcium carbonate:

H₂CO₃ + CaCO₃ ⟶ Ca(HCO₃)₂

The product, calcium bicarbonate, is soluble in water, so the chalk slowly dissolves.

(c) The dissolved substance present in the hard water does not convert into steam and gets deposited on the inner walls of the tube. Hence, the tubes become narrower and eventually less steam is produced.
When bore of the tube becomes very narrow, the pressure of steam increases so much that at times the boiler itself bursts. Hence, hard water is unfit for use in boilers.

(d) Ferric chloride (FeCl₃) is deliquescent, it absorbs moisture from the air and dissolves in the water it absorbs, eventually forming a saturated solution. This property makes it unstable in open air.

(e) Concentrated sulphuric acid H₂SO₄ is highly hygroscopic, meaning it absorbs water vapour from the air. If left open, it will absorb moisture and become diluted. To maintain concentration and prevent hazards, it should always be tightly stoppered.