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The K sp of FeS = 4 × 10 − 19 at 298 K . The minimum concentration of H + ions required to prevent the precipitation of FeS from a 0 .01 M solution Fe 2 + salt by passing H 2 S (Given H 2 S k a 1 × k b 1 = 10 − 21 )

Options

  1. A1.6 × 10 – 3 M
  2. B2.5 × 10 – 4 M
  3. C2.0 × 10 – 2 M
  4. D1.2 × 10 – 4 M

Correct answer

A. 1.6 × 10 – 3 M

Step-by-step solution

F e 2 + S – 2 = 4 × 10 – 19 ⇒ S – 2 = 4 × 1 0 – 19 1 × 1 0 – 2 = 4 × 10 – 17 M In order to precipitate F e S , S – 2 required is 4 × 10 – 17 M from 0.01 M F e 2 + salts. Now H + 2 4 × 1 0 – 17 0.1 = 1 × 10 – 21 ⇒ H + 2 = 2.5 × 10 – 6 ⇒ H + = 1.6 × 10 – 3

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