Find the ph of a 0.250 m solution of nac2h3o2. (the ka value of hc2h3o2 is 1.80*10-5). express your answer numerically to four significant figures.

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Chemistry

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24 June, 19:30

Find the ph of a 0.250 m solution of nac2h3o2. (the ka value of hc2h3o2 is 1.80*10-5). express your answer numerically to four significant figures.

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Paloma · Answer 1

Answer is: pH value of solution of NaC₂H₃O₂ is 9.07.

Chemical reaction: C₂H₃O₂⁻ + H₂O ⇄ HC₂H₃O₂ + OH⁻.

Ka (HC₂H₃O₂) = 1,8·10⁻⁵.

Ka · Kb = Kw.

1,8·10⁻⁵ mol/dm³ · Kb = 1·10⁻¹⁴ mol²/dm⁶; the ionic product of water at 25°C.

Kb (C₂H₃O₂⁻) = 1·10⁻¹⁴ mol²/dm⁶ : 1,8·10⁻⁵ mol/dm³.

Kb (C₂H₃O₂⁻) = 5,56·10⁻¹⁰ mol/dm³.

c (C₂H₃O₂⁻) = 0,25 M.

[OH⁻] = [HC₂H₃O₂] = x.

[C₂H₃O₂⁻] = 0,25 M - x.

Kb = [OH⁻] · [HC₂H₃O₂] / [C₂H₃O₂⁻].

5,56·10⁻¹⁰ = x² / (0,25 M - x).

Solve quadratic equation: x = [OH⁻] = 0,0000118 M.

pOH = - log[OH⁻] = - log (0,0000118M) = 4,93.

pH + pOH = 14.

pH = 14 - 4,93 = 9,07.