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 → Elements, Compounds, and Mixtures ↓


Definition of Mixture


Chemistry is the science that studies substances, how they interact, combine, and change to form new substances. At a basic level, chemistry introduces us to the concept of elements, compounds, and mixtures. Today, we are going to explore what a mixture is, its definition, types, properties, and examples.

What is a mixture?

A mixture is a combination of two or more substances that are not chemically bonded to one another. In a mixture, the substances retain their own properties and can often be separated by physical methods. When you have a mixture, each substance in it still appears and maintains its original properties.

Types of mixtures

There are mainly two types of mixtures: homogeneous mixture and heterogeneous mixture.

1. Homogeneous mixture

A homogeneous mixture has a uniform appearance and composition. It is also called a solution. Everything is mixed evenly, and you cannot see the separate parts.

Examples include:

  • sugar dissolved in water
  • salt water
  • air (a mixture of different gases)
H2O + C12H22O11 = Sugar solution H2O + NaCl = Saltwater

Consider a solution of salt in water. The salt dissolves in water and is dispersed uniformly, meaning it is the same throughout the water. Therefore, you cannot see individual particles of salt; they disappear into the water.

2. Heterogeneous mixture

Heterogeneous mixtures contain visibly distinct substances or phases. The individual components can be seen because they are not mixed uniformly. They can often be physically separated.

Examples include:

  • sand and water
  • salad
  • oil and water

For example, in a mixture of sand and water, the sand will settle at the bottom because sand does not dissolve in water, and they are clearly visible and can be separated by processes such as filtration.

Separation of mixtures

Since mixtures are made up of substances that are not chemically combined, they can be separated into their components by physical methods. Some common techniques for separating mixtures are as follows:

Filtration

Filtration is used to separate a solid from a liquid by passing the mixture through a porous material such as a filter. An example of this is separating sand from water.

Used in: Sand + H2O

Distillation

Distillation is a process in which components are separated based on the difference in their boiling points. An example of this is the separation of alcohol from water.

Used in: H2O + Alcohol

Evaporation

Evaporation is used to separate soluble solids from liquids. When one component evaporates, the other is left behind. An example of this is obtaining salt from salt water.

Used in: NaCl + H2O

Properties of mixtures

Mixtures have specific properties that distinguish them from pure substances:

  • The components of a mixture retain their original properties.
  • The proportions of the components may vary.
  • Mixtures can be separated into their components by physical methods.

Because mixtures are not chemically bonded, each substance in the mixture retains its own properties. For example, a can of mixed fruit juice does not transform the different juices into a new substance. You can still taste the individual fruits.

Visual example 1: Fruit salad

Consider a fruit salad made from apples, bananas and grapes. Each piece of fruit is a component of the mixture.

<svg width="200" height="150" xmlns="http://www.w3.org/2000/svg">
        <circle cx="50" cy="50" r="20" fill="red" />
        <text x="40" y="55" font-size="10" fill="white">Apple</text>
        <circle cx="150" cy="50" r="20" fill="yellow" />
        <text x="140" y="55" font-size="10" fill="black">Banana</text>
        <circle cx="100" cy="100" r="20" fill="purple" />
        <text x="90" y="105" font-size="10" fill="white">Grapes</text>
    </svg>

Visual example 2: Sand and iron filings

This mixture can be easily separated using a magnet, which will attract the iron filings and leave the sand behind.

<svg width="200" height="150" xmlns="http://www.w3.org/2000/svg">
        <rect x="20" y="60" width="160" height="20" fill="tan" />
        <text x="20" y="55" font-size="10" fill="black">Sand</text>
        <line x1="30" y1="80" x2="170" y2="80" stroke="gray" stroke-width="2" />
        <text x="30" y="95" font-size="10" fill="black">Iron filings</text>
    </svg>

Real examples of mixtures

  • Atmosphere: The air we breathe is a mixture of nitrogen, oxygen, carbon dioxide, and trace gases.
  • Seawater: It is a mixture of water, salt and other minerals.
  • Concrete: Made from a mixture of cement, water, sand and gravel.
  • Gunpowder: A mixture of sulfur, charcoal, and potassium nitrate.

Conclusion

Mixtures are important in both scientific studies and everyday life. Understanding the nature of mixtures and methods of separation is fundamental in chemistry because they apply to many scientific and industrial processes. Through this overview, you have explored the nature of mixtures, learned how they differ from pure substances, and how their components can sometimes be easily separated.


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Definition of Mixture

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