Answer to Question #312149 in Chemistry for Boyly

Question

What is the hydronium ion concentration of 1g of acetic acid in 100 ml of water?

Answer 1

Solution:

acetic acid = CH₃COOH

hydronium ion = H₃O⁺

The molar mass of CH₃COOH is 60.052 g/mol

Therefore,

(1 g CH₃COOH) × (1 mol CH₃COOH / 60.052 g CH₃COOH) = 0.01665 mol CH₃COOH

Liters of CH₃COOH solution = (100 mL soln) × (1 L / 1000 mL) = 0.1 L

Molarity of CH₃COOH = Moles of CH₃COOH / Liters of CH₃COOH solution

Therefore,

Molarity of CH₃COOH = (0.01665 mol) / (0.1 L) = 0.1665 mol/L = 0.1665 M

Acetic acid (CH₃COOH) is a weak acid because it partially dissociates in an aqueous solution or it does not ionize completely in solution to produce hydronium ions (H₃O⁺).

Equation representing the dissociation of CH₃COOH:

CH₃COOH(aq) + H₂O(l) ⇋ H₃O⁺(aq) + CH₃COO⁻(aq)

ICE Table:

According to the ICE Table:

[H₃O⁺] = [CH₃COO⁻] = X

[CH₃COOH] = 0.1665 − X ≈ 0.1665 M (assume that 0.1665 >> X)

The K_a expression for the dissociation of CH₃COOH:

K_a = 1.75×10⁻⁵ (for CH₃COOH)

Therefore,

1.75×10⁻⁵ = [X] × [X] / [0.1665]

2.914×10⁻⁶ = X²

X = (2.914×10⁻⁶)^1/2 = 0.0017

[H₃O⁺] = X = 0.0017 M = 1.7×10⁻³ M

[H₃O⁺] = 1.7×10⁻³ M

Answer: The hydronium ion (H₃O⁺) concentration is 1.7×10⁻³ M