8.6
오스트발트의 희석 법칙
농도 'c' 를 가진 이진 전해질 AB를 생각해 보자. 이 이온은 가역적으로 이온으로 해리된다. 이 해리의 정도는 ⍺으로 표현됩니다. 즉, 각 이온 종의 평형 농도는 ⍺c로 표현할 수 있습니다. 이와 더불어, 평형 상태에서 해리되지 않은 전해질 비율은 (1−⍺)로 주어…
아레니우스의 전해 해리 이론에 기반한 오스트발트 희석 법칙은 수용성 전해질 용액 내 평형을 설명합니다.
전해질 AB를 1리터당 'c' mol 농도로 고려해 보세요. 이 AB는 가역적으로 이온으로 해리됩니다.
α가 해리의 정도라면, 각 이온은 평형 농도인 cα를 가지며, 해리되지 않은 분획 (1 − α)은 c(1 − α)의 농도를 가진다. 이 용어들은 평형 상수 K, 즉 해리 상수를 정의합니다.
오스트발트 희석 법칙은 아세트산과 NH₄OH와 같은 약한 전해질에만 적용됩니다.
HCl과 NaF 같은 강한 전해질은 거의 완전히 해리되어 있으며, α 거의 1에 가깝습니다. 이 조건들 하에서 (1 − α) 는 0에 가까워져 법칙이 수학적으로 무효가 된다.
강한 전해질에 대한 법칙의 실패는 용해 시 물의 높은 유전율이 정전기력을 약화시켜 거의 완전한 해리를 초래하기 때문에 발생합니다. 그 결과 이온-분자 평형이 존재하지 않으며, 오스트발트의 희석 법칙은 적용되지 않는다.
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Q1: What is Ostwald's dilution law and how does it relate to electrolyte dissociation?
Ostwald's dilution law explains equilibrium in aqueous electrolyte solutions based on Arrhenius' theory of electrolytic dissociation. For an electrolyte AB at concentration c, the dissociation constant K equals cα²/(1−α), where α is the degree of dissociation. This law describes how weak electrolytes like acetic acid and NH₄OH reversibly dissociate into ions at equilibrium.
Q2: Why does Ostwald's dilution law fail for strong electrolytes?
Strong electrolytes like HCl and NaF are almost completely dissociated, with α approaching one, making (1−α) approach zero. This renders the law mathematically invalid. Water's high dielectric constant weakens electrostatic forces, causing near-complete dissociation and eliminating the ion-molecule equilibrium that the law requires.
Q3: How do you calculate equilibrium concentrations using the degree of dissociation?
For an electrolyte AB with concentration c and degree of dissociation α, each ion has equilibrium concentration cα, while the undissociated fraction has concentration c(1−α). These concentrations define the dissociation constant K, which governs the equilibrium state of weak electrolyte solutions.
Q4: What is the difference between weak and strong electrolytes in terms of dissociation?
Weak electrolytes like acetic acid partially dissociate, with α significantly less than one, allowing Ostwald's dilution law to apply. Strong electrolytes like NaCl and NaF are electrovalent compounds formed by electron transfer; they dissociate almost completely with α near one, making the law inapplicable to them.
Q5: How does the dielectric constant of a solvent affect electrolyte dissociation?
According to Coulomb's law, the dielectric constant of the medium affects electrostatic force strength and conductivity. Water's high dielectric constant weakens electrostatic forces between ions, promoting near-complete dissociation of strong electrolytes and enabling ion mobility for electrical conduction in solutions.
Q6: What is the simplified form of Ostwald's dilution law for very weak electrolytes?
For very weak electrolytes where α is much less than one, the term (1−α) approximates to one. The dissociation constant simplifies to K ≈ cα², making calculations more straightforward for solutions with minimal dissociation and allowing easier prediction of equilibrium behavior.
Q7: What structural difference exists between strong electrolytes and weak electrolytes?
Strong electrolytes like NaCl and NaF are electrovalent compounds composed solely of ions in their crystal structure, not molecules. When dissolved in water, these ions gain mobility and conduct electricity. Weak electrolytes exist as molecules that partially dissociate into ions upon dissolution in solution.