Respuesta :
By using the formula, mass = density x volume, we calculate mass in grams
20.0 mL CH₃COOH x (1.05 g / mL) = 21.0 g CH₃COOH
To find the moles, molar mass of CH₃COOH = 60.05g/mol
21.0 g CH₃COOH x (1 mole CH₃COOH / 60.05 g CH₃COOH)
= 0.350 moles CH₃COOH
To find molarity,
[CH₃COOH] = moles CH₃COOH / L of solution = 0.350 /
1.40 = 0.250 M CH₃COOH
When CH₃COOH is dissolved in water, it produces
small and equal amounts of H₃O⁺+ and C₂H₃O₂⁻.
Molarity , CH₃COOH + H₂O <==> H₃O⁺ + C₂H₃O₂⁻
Initial 0.250 0 0
Change -x x x
Equilibrium 0.250-x x x
Kₐ = [H₃O⁺][C₂H₃O₂⁻] / [HC₂H₃O₂] = (x)(x) /
(0.250-x) = 1.8 x 10⁻⁵
Since Kₐ is relatively small, we can neglect the -x term after 0.250 to simplify
x² / 0.250 = 1.8 x 10⁻⁵
x² = 4.5 x 10⁻⁶
x = 2.1 x 10⁻³ = [H₃O⁺]
pH = -log [H₃O⁺] = -log (2.1 x 10⁻³) = 2.68
