The common zeolite used for softening of hard water is Natrolite. Its molecular formula is:

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DSSSB PGT Chemistry (Female) Official Paper (Held On: 06 Jul, 2018 Shift 1)

Answer 1

CONCEPT:

Zeolites for Water Softening

Zeolites are microporous minerals that are commonly used for the softening of hard water.
The common zeolite used for this purpose is Natrolite.
Zeolites work by ion exchange, where calcium (Ca²⁺) and magnesium (Mg²⁺) ions in hard water are replaced with sodium (Na⁺) ions.

EXPLANATION:

The molecular formula of Natrolite is Na₂O·Al₂O₃·3SiO₂·2H₂O.
In this formula:
- Na₂O represents sodium oxide, which provides sodium ions for ion exchange.
- Al₂O₃ represents aluminum oxide, which forms part of the zeolite structure.
- 3SiO₂ represents silicon dioxide, which contributes to the tetrahedral framework of the zeolite.
- 2H₂O represents water molecules within the zeolite structure.
Natrolite is highly effective in removing calcium and magnesium ions from hard water, thus softening it.

Therefore, the correct molecular formula of Natrolite is Na₂O·Al₂O₃·3SiO₂·2H₂O.