Question

find the [S^-2] in a saturated solution of 0.1M H2S if the PH WAS adjusted to 2 by adding HCl.Ka of H2S is 1.2× 10^-21​

Answer 1

Explanation:

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Answer 2

Given:

pH of the solution = 2

[H₂S] = 0.1 M

Kₐ = 1.2×10⁻²¹

To find:

The concentration of S⁻²

Calculation:

The reaction will be  

   H₂S  ⇄ 2H⁺ + S²⁻

We know the formula pH = -log[H⁺]

=> 2 = -log[H⁺]

    log[H⁺] = -2

    [H⁺] = 10⁻² M

=> Kₐ = [H⁺]²[S⁻²] / [H₂S]

    1.2×10⁻²¹ = (10⁻²)² × [S⁻²] / 0.1

    1.2×10⁻²¹ = 10⁻³ × [S⁻²]

    [S⁻²] = 1.2×10⁻¹⁸ M

The concentration of S⁻² ( [S⁻²] )= 1.2×10⁻¹⁸ M