DB

Separating a Mixture of Liquids

Separating a Mixture of Liquids

  • Essential Question: How do we identify and separate a homogeneous mixture of liquids using boiling point?

Separating Liquid Mixtures

  • Mixtures of different liquids can be identified using:

    • Density

    • Odor

    • Boiling point

    • Flammability tests

  • Method of separation: All of these tests can be performed using fractional distillation.

Boiling Point

  • Definition: Boiling point is a physical property determined by various factors.

  • Factors influencing boiling point:

    • Intermolecular Forces (IMF):

    • The stronger the intermolecular forces, the higher the boiling point and melting point of a liquid.

    • Molecular Size: Larger molecules generally have higher boiling points due to increased van der Waals forces.

    • Atmospheric Pressure: The greater the pressure, the higher the boiling point.

  • Assumption: Under normal conditions, the atmospheric pressure is considered constant, but the actual pressure can fluctuate based on location and altitude.

Definitions

  • Boiling Point: The temperature at which a liquid turns into a vapor.

    • Example: Water boils at 100^{ ext{o}} ext{C}.

  • Intermolecular Forces: The attractive force that holds molecules together in a substance.

    • Example: Water molecules “stick” together to form drops.

Determining Boiling Point

  • To accurately determine boiling point:

    • Create a Time vs. Temperature graph.

    • By recording temperature changes over time, the graph will display features that can be interpreted to find the boiling point.

Reading the Graph

  • Temperature Increase: The temperature should increase steadily until it reaches a plateau.

    • Plateaus: Identified when the temperature remains constant over several measurements, indicating the boiling point.

    • Graph Features:

    • Plateau 1

    • Plateau 2

    • Rising Temperature

Number of Liquids Present

  • Determining the number of liquids: Can be ascertained by counting the number of plateaus in the graph.

Plateaus Can Be Imperfect

  • Plateau Quality: Ideally, plateaus would be perfectly flat, but slight increases or decreases can occur due to factors outside of experimental control.

  • Logic Application: In such cases, logic must be applied to estimate the actual boiling point, as very slight temperature increases over time may still represent a plateau.

Separating a Mixture of Crude Oil

  • Description of Crude Oil: A thick, black semi-liquid mixture found underground, derived from dead plants and animals that decayed over millions of years.

  • Usage: Crude oil cannot be utilized directly and must be separated into useful products such as:

    • Gasoline: Used for cars

    • Diesel: Used for trucks

    • Kerosene: Used as jet fuel

    • Asphalt: Used for roads

    • Lubricating Oil: Used for machines

    • Petrochemicals: Used for plastics and fertilizers

How Fractional Distillation Works

  • Process:

    1. Heat the crude oil in a large tower called a fractionating column.

    2. As the oil boils, different components evaporate at varying temperatures.

    3. The vapor rises up the tower, where it is cooler at the top and hotter at the bottom.

    4. Condensation: Different hydrocarbons condense (turn back into liquid) at different levels within the column, allowing for effective separation.