Grade 7
  1. Introduction to Chemistry  1.1. What is Chemistry?  1.2. Importance of chemistry in daily life  1.3. Branches of chemistry  1.4. Scientific Method in Chemistry  1.5. Laboratory Safety Rules and Precautions  1.6. Common Laboratory Equipment and Their Uses  1.7. Units of measurement in chemistry
  2. Matter and its properties  2.1. Definition of Matter  2.2. Classification of matter  2.3. Properties of matter  2.3.1. Physical properties  2.3.2. Chemical properties  2.4. States of matter  2.4.1. Solid state  2.4.2. Fluid state  2.4.3. Gaseous state  2.4.4. Plasma and Bose–Einstein condensates  2.5. Changes in the states of matter  2.5.1. Melting and freezing  2.5.2. Evaporation and Condensation  2.5.3. Sublimation and deposition  2.6. Density and its applications  2.7. Diffusion and its importance
  3. Elements, Compounds, and Mixtures  3.1. Definition of the element  3.2. Classification of elements  3.3. Metals, Nonmetals and Metalloids  3.4. Noble gases and their properties  3.5. Introduction to the Periodic Table  3.6. Definition of Compound  3.7. Properties of Compounds  3.8. Introduction to Chemical Formulas  3.9. Definition of Mixture  3.10. Types of mixtures  3.10.1. Homogeneous mixture  3.10.2. Heterogeneous mixtures  3.11. Difference Between Compounds and Mixtures  3.12. Solutions, Colloids and Suspensions
  4. Separation of mixtures  4.1. Need for separation of mixtures  4.2. Separation methods  4.2.1. Filtration  4.2.2. Sedimentation and decantation  4.2.3. Evaporation  4.2.4. Crystallization  4.2.5. Distillation  4.2.6. Chromatography  4.2.7. Magnetic Separation  4.2.8. Centrifugation
  5. Atomic Structure  5.1. Introduction to Atoms  5.2. Structure of the atom  5.2.1. Nucleus and electron cloud  5.3. Subatomic particles  5.3.1. Proton  5.3.2. Neutron  5.3.3. Electrons  5.4. Atomic number and mass number  5.5. Isotopes and their uses  5.6. Ions and ion formation
  6. Periodic table  6.1. Introduction to the Periodic Table  6.2. Groups and periods  6.3. Trends in the Periodic Table  6.3.1. Atomic Size  6.3.2. Metallic and non-metallic character  6.3.3. Electronegativity  6.3.4. Reactivity of the elements  6.4. Alkali metals and their properties
  7. Chemical bond  7.1. Why do atoms form bonds?  7.2. Types of chemical bonds  7.2.1. Ionic bond  7.2.2. Covalent bond  7.2.3. Metal Bond  7.3. Properties of Ionic and Covalent Compounds  7.4. Intermolecular forces
  8. Chemical reactions  8.1. Introduction to Chemical Reactions  8.2. Signs of a chemical reaction  8.3. Types of Chemical Reactions  8.3.1. Combination Reactions  8.3.2. Decomposition reactions  8.3.3. Displacement reactions  8.3.4. Double displacement reactions  8.3.5. Combustion reactions  8.4. Law of conservation of mass  8.5. Balancing simple chemical equations
  9. Acids, Bases and Salts  9.1. Definition of Acid and Base  9.2. Properties of Acids  9.3. Properties of bases  9.4. pH Scale and Indicators  9.5. Neutralization reactions  9.6. Common Acids and Bases in Everyday Life  9.7. Preparation and use of salts  9.8. Strong and weak acids and bases
  10. Solutions and Solubility  10.1. Definition of Solution  10.2. Components of the solution  10.2.1. Solvent  10.2.2. solute  10.3. Factors Affecting Solubility  10.4. Concentration of solutions  10.5. Saturated and unsaturated solutions  10.6. Colloids and suspensions  10.7. Solubility curve and its interpretation
  11. Air and atmosphere  11.1. Composition of air  11.2. Properties of gases in the air  11.3. Importance of Oxygen and Carbon Dioxide  11.4. Air pollution and its effects  11.5. Greenhouse effect and global warming  11.6. Ways to reduce air pollution  11.7. Ozone layer and its importance
  12. Water and its importance  12.1. Properties of Water  12.2. Water as the universal solvent  12.3. Importance of water for life  12.4. Water pollution and its effects  12.5. Water Purification  12.5.1. Filtration  12.5.2. boil  12.5.3. Chlorination in water purification  12.5.4. reverse osmosis  12.6. Hard and soft water  12.7. Water cycle and its importance
  13. Fuel and energy  13.1. Types of fuel  13.1.1. Fossil fuels  13.1.2. Renewable energy sources  13.2. Combustion and energy release  13.3. Global warming and its effects  13.4. Alternative sources of energy  13.5. Ways to conserve energy
  14. Metals and Nonmetals  14.1. Physical and chemical properties of metals  14.2. Physical and Chemical Properties of Non-Metals  14.3. Difference Between Metals and Nonmetals  14.4. Uses of metals and nonmetals  14.5. Corrosion of metals and its prevention  14.6. Alloys and their importance
  15. Plastics and polymers  15.1. Natural and synthetic polymers  15.2. Properties of plastics  15.3. Biodegradable and Non-Biodegradable Plastics  15.4. Environmental impact of plastic  15.5. Recycling and waste management in plastics and polymers  15.6. Daily Uses of Polymers
  16. Introduction to Organic Chemistry  16.1. Basic definitions of organic chemistry  16.2. Carbon Compounds in Daily Life  16.3. Hydrocarbons  16.4. Simple functional groups (alcohols and carboxylic acids)  16.5. Importance of organic compounds in industry

Grade 7 → Separation of mixtures → Separation methods ↓


Chromatography


Chromatography is a fascinating method of separating mixtures that scientists use to discover, analyze, and understand the components of different substances. At its core, chromatography means separating the parts of a mixture so that each part can be studied closely and more information can be obtained about the whole. It is an incredibly useful process in many fields such as chemistry, biology, and even medicine.

What is a mixture?

Before delving deeper into chromatography, let's understand what a mixture is. A mixture is a combination of two or more substances, where each substance retains its individual chemical properties. For example, if you mix sand with salt, you get a mixture. Each part of the mixture (sand and salt) retains its own properties.

Mixtures may be homogeneous or heterogeneous:

  • Homogeneous mixtures are completely uniform. An example of this is salt water. You cannot see the individual salt particles because they are completely dissolved in the water.
  • Heterogeneous mixtures have different regions and the different substances can be seen. An example of this is a salad, where you can see different components such as lettuce, tomatoes, and cucumbers.

Basics of chromatography

Chromatography is based on the principle of separating a mixture into two phases:

  • Stationary phase: It is the phase that does not move. It can be solid or liquid.
  • Mobile phase: This is the phase that moves. It can be a liquid or a gas.

The basic idea of chromatography is to move the components of a mixture at different speeds over or through the stationary phase using the mobile phase. This causes them to separate and collect at different points. In other words, each component of the mixture interacts differently with the stationary and mobile phases, causing them to travel in different ways.

Types of chromatography

There are many types of chromatography, but we will focus on three common types that demonstrate the process well:

  1. Paper chromatography:

    Paper chromatography is one of the simplest forms of chromatography and is a great way to demonstrate the process. It uses a strip of paper as the stationary phase and a solvent (usually a liquid) as the mobile phase.

    You can try it as follows:

    • Take a strip of special chromatography paper or regular filter paper.
    • Draw a line using a pencil (do not use a pen as the ink will bleed) 2cm from the bottom.
    • Place a small dot of ink or dye on the line.
    • Place the strip in a container with a small amount of solvent; make sure the solvent level is below the pencil line.
    • Watch as the solvent moves up the paper, separating the ink or paint into its individual colors.
    paper Solvent front
  2. Thin layer chromatography (TLC):

    Like paper chromatography, TLC uses a thin layer of silica gel or alumina spread on a flat, inert substrate as the stationary phase. The mobile phase used is usually a solvent.

    The basic idea is this:

    • Put a small spot of the mixture near the bottom of the TLC plate.
    • Submerge the plate in a shallow pool of solvent in a sealed container.
    • The solvent rises up the plate by capillary action, separating the mixture as in paper chromatography.
    • When the solvent has travelled a certain distance, remove the plate. The separated components appear as spots at different heights on the plate.
  3. Column chromatography:

    Column chromatography is used on a larger scale than paper or TLC. It involves a column filled with a stationary phase (often silica gel or alumina) and a liquid mobile phase.

    How it works:

    • Pour the mixture into the top of a column filled with the stationary phase.
    • Pour the solvent (mobile phase) into the column.
    • Different components of the mixture move at different speeds and get separated as they move down the column.
    • Collect the separated components as they pass down the column.
    Solvent

Why is chromatography useful?

Chromatography is incredibly useful because it can separate very complex mixtures into easily understood parts. Here are some reasons why it stands out:

  • Identification: Scientists can identify different substances in a mixture.
  • Purification: This allows the purification of single components from a mixture.
  • Analysis: Used to analyze the presence and amount of substances in a mixture.

Real-life applications

Chromatography is everywhere in the scientific world and beyond:

  • Medical tests: It helps to identify substances in blood and urine tests.
  • Food industry: Ensuring taste and nutritional quality.
  • Environmental studies: It is used to detect pollutants in air, water and soil.
  • Forensic science: Important in the analysis of samples from crime scenes.

Understanding the components of chromatography

Let's consider the mixture being separated and the apparatus used. The interaction between the mixture and the stationary phase is important because it helps separate the components. Different components will have different affinities to the stationary phase:

  • High affinity: components that interact strongly with the stationary phase will move slowly.
  • Low affinity: Components that interact less will move more rapidly.

The nature of the mobile phase is equally important because it affects how the components interact with the stationary phase and with each other. The selection of an appropriate mobile phase is often a key decision in designing a successful chromatographic separation.

Practical example using paper chromatography

Let's imagine an experiment using marker ink. If you use a black marker, it may actually be a mixture of several colors. This is how you can discover hidden colors through chromatography:

    1. You begin by marking a starting line on your paper.
    2. Then, you make several small dots with different colors of black marker.
    3. Place the bottom side of the paper in a solvent, such as water or alcohol.
    4. Watch as the solvent moves upward and begins carrying the ink with it.
    5. As the solvent reaches the paper, different colors will appear at different levels.

Through this simple demonstration, you can see how chromatography reveals the complexity behind something as simple as "black ink."

Conclusion

Chromatography is an elegantly simple yet extremely powerful technique for separating and identifying components in a mixture. From its humble beginnings as an experimental tool for chemists, it has become an essential technique applied in countless laboratories worldwide. As you continue to explore the world of mixtures and their separations, remember that chromatography provides a window into the microcosm of chemistry, revealing the hidden wonders of diverse substances.


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Chromatography

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