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A crystalline hydrated salt on being heated loses 45.6% of its weight. Percentage composition of anhydrous salt is Al - 10.5 %, K - 15.1 %, S - 24.8 %, O - 49.6 %. Find molecular formula of salt (hydrated) (M = 948 g/mol for hydrated salt).

Options

  1. AK 2 SO 4 .Al 2 (SO 4 ) 3 .24H 2 O
  2. BK 2 SO 4 .Al 2 (SO 4 ) 3 .12H 2 O
  3. CK 2 SO 4 .Al 2 (SO 4 ) 3 .6H 2 O
  4. DK 2 SO 4 .Al 4 (SO 4 ) 6 .48H 2 O

Correct answer

A. K 2 SO 4 .Al 2 (SO 4 ) 3 .24H 2 O

Step-by-step solution

For anhydrous salt Element Al K S O Atomic ratio 1 0 · 5 2 7 1 5 · 1 3 9 2 4 · 8 3 2 4 9 · 6 1 6 0 · 3 9 0 · 3 9 0 · 7 8 3 · 1 0 Empirical formula of anhydrous salt = KAlS 2 O 8 E.F mass of Anhydrous salt = 258 g/mol Mass of Moisture = 2 5 8 × 4 5 · 6 5 4 · 4 = 2 1 6 g = 2 1 6 1 8 ≈ 1 2 mole Empirical formula of Anhydrous salt KAlS 2 O 8 .12H 2 O E F Mass = 2 5 8 + 2 1 6 = 4 7 4 g/Empirical formula mass n = Mole Mass E.F. Mass = 9 4 8 4 7 4 = 2 Molecular Formula = K 2 Al 2 S 4 O 16 .24H 2 O = K 2 SO 4 .Al 2 (SO 4 )

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