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Chapter 3- Separation and Purification

  • A pure substance consists of a single element or compound.

  • Pure substances have a constant and fixed boiling and melting point.

  • Impurities cause variation in the melting and boiling points of the substance. Therefore, they can be used to determine if a substance is pure or not.

  • Different purification techniques can be used to separate and purify substances.

Method

Usage

Example

Filtration

Insoluble solid from liquid

Sand and water

Evaporation to dryness

Soluble solid from a solution

To get salt from salt solution

Crystallization

Pure solid from a solution

To get Copper (II) sulfate from water

Solvent in which only one solid is soluble

A Mixture of two solids

Sand and salt

Sublimation

Solid that sublimes with one which doesn’t

Iodine and sand

Magnet

Magnetic substance from a non-magnetic one

Iron filings and sulfur

Simple distillation

Pure solvent (liquid) from the solution

To get water from a salt solution

Separating funnel

Immiscible liquids

Oil and water

Fractional distillation

Miscible liquids with different boiling points

Water and ethanol

Chromatography

Components that dissolve in the same solvent

Different dyes

Centrifugation

Mixtures by spinning

Blood cells from plasma

Decanting

Liquid  and insoluble particles

Rice from water

STEPS TAKEN DURING DISTILLATION:

  1. Thermometer should be placed beside the sidearm of the distillation flask, not inside the liquid.

  2. Water outlets should be positioned in the correct way with cold water in from the bottom and leaving from the top.

  3. The condenser slopes downward so the pure solvent runs to the flask/beaker.

  4. If the distillate is volatile, it has to be kept in a container containing ice so it doesn’t evaporate.

Chromatography

  • Different components separated using chromatography have distinct Rf values or Retention factors.

  • Rf value is calculated by dividing the distance moved by the solute by the distance moved by the solvent.

  • Rf values can be matched by the already known values to identify the component.

  • Sometimes, the components are transparent such as amino acids. A locating agent (e.g. Ninhydrin) is sprayed on the chromatogram to make them visible.

Chapter 3- Separation and Purification

  • A pure substance consists of a single element or compound.

  • Pure substances have a constant and fixed boiling and melting point.

  • Impurities cause variation in the melting and boiling points of the substance. Therefore, they can be used to determine if a substance is pure or not.

  • Different purification techniques can be used to separate and purify substances.

Method

Usage

Example

Filtration

Insoluble solid from liquid

Sand and water

Evaporation to dryness

Soluble solid from a solution

To get salt from salt solution

Crystallization

Pure solid from a solution

To get Copper (II) sulfate from water

Solvent in which only one solid is soluble

A Mixture of two solids

Sand and salt

Sublimation

Solid that sublimes with one which doesn’t

Iodine and sand

Magnet

Magnetic substance from a non-magnetic one

Iron filings and sulfur

Simple distillation

Pure solvent (liquid) from the solution

To get water from a salt solution

Separating funnel

Immiscible liquids

Oil and water

Fractional distillation

Miscible liquids with different boiling points

Water and ethanol

Chromatography

Components that dissolve in the same solvent

Different dyes

Centrifugation

Mixtures by spinning

Blood cells from plasma

Decanting

Liquid  and insoluble particles

Rice from water

STEPS TAKEN DURING DISTILLATION:

  1. Thermometer should be placed beside the sidearm of the distillation flask, not inside the liquid.

  2. Water outlets should be positioned in the correct way with cold water in from the bottom and leaving from the top.

  3. The condenser slopes downward so the pure solvent runs to the flask/beaker.

  4. If the distillate is volatile, it has to be kept in a container containing ice so it doesn’t evaporate.

Chromatography

  • Different components separated using chromatography have distinct Rf values or Retention factors.

  • Rf value is calculated by dividing the distance moved by the solute by the distance moved by the solvent.

  • Rf values can be matched by the already known values to identify the component.

  • Sometimes, the components are transparent such as amino acids. A locating agent (e.g. Ninhydrin) is sprayed on the chromatogram to make them visible.