4.2
증류: 증기-액체 평형
증류는 혼합물에서 서로 다른 원소의 끓는점 특성을 활용하는 분리 기술입니다. 증류를 수행하려면 끓는점(최소 20°C)의 차이가 큰 두 액체의 혼합 가능한 혼합물을 가열하는 것부터 시작합니다. 용액이 가열되어 휘발성이 높은 성분의 거품점에 도달하면 휘발성이 높은 성분의…
증류법은 다양한 분대가 수증기와 액체 단계 사이에서 배부되는 방법을 나타내는 다른 수증기 액체 평형 관계를 반영하는 현저하게 다른 끓는점을 가진 혼화성 액체를 분리한다.
혼합물이 가열되면 첫 번째 증기 기포가 더 휘발성이 높은 성분의 기포 지점에 나타납니다.
증기는 증류액이라고 하는 액체로 응축되어 혼합물과 별도로 수집됩니다. 초기 증류액은 휘발성이 더 낮은 성분이 여전히 액체상을 선호하기 때문에 더 휘발성 성분이 풍부합니다.
휘발성이 더 높은 성분이 끓어남에 따라 끓는 상태를 유지하는 데 필요한 온도가 증가합니다.
따라서 증류가 진행됨에 따라 휘발성이 적은 성분의 증발 속도가 증가하여 중간 증류 액을 더 균일 한 혼합물로 만듭니다. 최종 증류액은 휘발성이 적은 성분이 풍부합니다.
View the full transcript and gain access to JoVE Core videos
Q1: What is vapor-liquid equilibrium and why does it matter in distillation?
Vapor-liquid equilibrium describes how components distribute between vapor and liquid phases during distillation. It determines which component boils first and how the composition of the distillate changes throughout the process. Understanding this equilibrium helps predict boiling points and identify when distillation ends based on mole fractions of the mixture components.
Q2: Why does the temperature increase as distillation progresses?
As the more volatile component boils off, the mixture becomes enriched in the less volatile component, which requires higher temperatures to vaporize. The temperature rise reflects the changing composition of the remaining liquid. This temperature change is directly related to the vapor-liquid equilibrium of the binary mixture and helps indicate the distillation stage.
Q3: How does the composition of distillate change during a distillation experiment?
Early distillate is rich in the more volatile component because it vaporizes first. As distillation continues, the middle distillate becomes a more even mixture of both components. The final distillate is rich in the less volatile component. This compositional progression reflects the changing vapor-liquid equilibrium as the mixture composition shifts.
Q4: What is a vapor-liquid equilibrium diagram and how is it used?
A vapor-liquid equilibrium diagram plots equilibrium temperature against the mole fraction of components in a binary mixture. The x-axis shows mole fraction and the y-axis shows temperature. These diagrams, available in literature for common mixtures, allow chemists to determine boiling points, predict liquid and vapor composition at any temperature, and identify when distillation will end.
Q5: What minimum boiling point difference is required for effective distillation?
Distillation requires miscible liquids with a significant difference in boiling points, typically at least 20 degrees Celsius. This substantial difference ensures that the more volatile component vaporizes preferentially, allowing effective separation. Without sufficient boiling point difference, the vapor-liquid equilibrium relationships cannot provide adequate separation between components.
Q6: How does a condenser work in the distillation apparatus?
The condenser is a glass tube with separate inner and outer sections. Vapor travels into the inner section where it contacts cold water flowing through the outer section. This temperature difference condenses the vapor back to liquid, called distillate, which is then collected in a graduated cylinder or test tube for analysis.
Q7: What determines when a component appears in the vapor phase during distillation?
A component enters the vapor phase when the mixture reaches its bubble point temperature. The more volatile component has a lower bubble point and vaporizes first. As heating continues and composition changes, the bubble point rises, allowing the less volatile component to eventually vaporize. This behavior is governed by the states of matter and phase changes occurring in the mixture.