For the dissociation of a very weak acid, HA, in water

Question

BlackTom AI · Accepted Answer

We start by restating the question to focus on the expression for the acid dissociation constant (Ka) of a very weak acid HA in water.

Option 1: 'Ka = [H3O+][ A−]'. This misses the necessary division by the undissociated acid concentration [HA]. Without the denominator, this cannot be the proper Ka expression, which measures the ratio of products to reactant.

Option 2: 'Ka = [HA][H3O+][ A−]'. Here all species appear multiplied together, which incorrectly combines reactants and products and does not form a ratio. It overshoots by including [HA] in the numerator and lacks division by the correct term, so this is not correct.

Option 3: 'Ka = [H3O+][ A−] / [HA]'. This matches the standard definition for a monoprotic acid dissociation in water: HA ⇌ H3O+ + A−, with Ka = ([H3O+][A−]) / [HA]. It correctly includes the concentrations of the products in the numerator and the undissociated acid in the denominator.

Option 4: 'Ka = [H3O+][ A−] / [H2O]'. This would imply dependence on the solvent concentration, which is constant for water and not included in the Ka expression for a weak acid in aqueous solution. The standard Ka expression divides by [HA], not by [H2O], so this is incorrect.

Option 5: 'Ka = [HA] / [A−][H3O+]'. This inverts the correct ratio, effectively swapping the numerator and denominator in a way that does not reflect the equilibrium expression for Ka. It misrepresents the relationship between reactants and products in the dissociation.

Across all options, the key point is that Ka is the ratio of the product of the hydronium and conjugate base concentrations to the concentration of the weak acid that remains undissociated, for the equilibrium HA ⇌ H3O+ + A−. The only choice that matches this definition is Option 3.

For the dissociation of a very weak acid, HA, in water单项选择题

类似问题

Write an expression for the acid ionization constant (Ka) for the dissociation of the following weak acid H2CO3.

A 0.10 M solution of a weak acid, HX, is 0.059% ionized. Evaluate Ka for the acid.

The pH of a solution of a 0.15 M solution of HOCl is 4.14. What is the Ka for HOCl?

The larger the value of Ka

The pH of a 0.800 M aqueous solution of a weak acid is 1.99. What is the value of Ka for this acid?

A 0.025 M solution of a weak acid has a percent ionization of 3.2%. What is the Ka of the weak acid?

Based on the following titration curve, what is the Ka for this weak acid?

Which of the following trees corresponds to a potential parse of the ambiguous sentence below, with correct syntactic categories? Some diagnostics are provided.

更多留学生实用工具

智能学习助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单