Grade 6
  1. Introduction to Chemistry  1.1. What is Chemistry?  1.2. Importance of chemistry in daily life  1.3. Branches of chemistry  1.4. Safety rules in chemistry laboratory  1.5. Common Laboratory Equipment and Their Uses
  2. Matter and its states  2.1. Definition of Matter  2.2. Properties of matter  2.3. States of matter  2.4. Solid state  2.5. Fluid state  2.6. Gaseous state  2.7. Plasma state  2.8. Changes in the states of matter  2.9. Melting and freezing  2.10. Evaporation and Condensation  2.11. Sublimation  2.12. Deposit
  3. Physical and chemical changes  3.1. Definition of Physical Change  3.2. Examples of physical change  3.3. Definition of Chemical Change  3.4. Examples of chemical change  3.5. Difference Between Physical and Chemical Changes  3.6. Indicators of Chemical Change
  4. Elements, Compounds, and Mixtures  4.1. Definition of the element  4.2. Classification of elements  4.3. Metals  4.4. Non metallic  4.5. Metalloids  4.6. Noble gases  4.7. Definition of compound  4.8. Properties of Compounds  4.9. Definition of Mixture  4.10. Types of mixtures  4.11. Homogeneous mixture  4.12. Heterogeneous mixtures
  5. Separation of mixtures  5.1. The need for isolation  5.2. Separation methods  5.3. Handpicking and winnowing  5.4. Filtration  5.5. Sedimentation and decantation  5.6. Evaporation  5.7. Crystallization  5.8. Distillation  5.9. Magnetic Separation  5.10. Chromatography
  6. Air and its composition  6.1. Components of air  6.2. Importance of Oxygen  6.3. The importance of nitrogen in the air and its composition  6.4. Carbon dioxide in the atmosphere  6.5. The role of water vapor and other gases in air and its composition  6.6. Properties of Air  6.7. Uses of air  6.8. Air pollution and its effects
  7. Water and its properties  7.1. Importance of Water  7.2. Sources of water  7.3. Properties of water  7.4. Water as the universal solvent  7.5. Water Purification  7.6. Water purification methods (boiling, filtration, chlorination)  7.7. Water cycle  7.8. Water conservation  7.9. Water pollution and its effects
  8. Acids, Bases and Salts  8.1. Definition of Acid  8.2. Properties of Acids  8.3. Examples of Acids  8.4. Definition of Bases  8.5. Properties of bases  8.6. Examples of Bases  8.7. Definition of Salt  8.8. Neutralization reaction  8.9. pH Scale and Indicators  8.10. Uses of Acids, Bases and Salts
  9. Introduction to the Periodic Table  9.1. History of the Periodic Table  9.2. Arrangement of elements in the periodic table  9.3. Groups and periods  9.4. Importance of periodic table  9.5. First 10 elements and their symbols
  10. Metals and Nonmetals  10.1. Properties of Metals  10.2. Properties of Non-Metals  10.3. Difference Between Metals and Nonmetals  10.4. Uses of metals and nonmetals  10.5. Corrosion of metals and its prevention
  11. chemical reactions  11.1. Introduction to Chemical Reactions  11.2. Types of Chemical Reactions  11.3. combustion reaction  11.4. Oxidation and Reduction  11.5. Simple chemical equations  11.6. Rusting of iron
  12. Fuel and energy  12.1. Types of fuel  12.2. Fossil fuels  12.3. Renewable and non-renewable sources of energy  12.4. Energy Conservation  12.5. Alternative sources of energy (solar, wind, hydropower)
  13. Plastic and fiber  13.1. Natural and synthetic fibers  13.2. Properties of plastics  13.3. Advantages and disadvantages of plastic  13.4. Recycling of plastic  13.5. Biodegradable and non-biodegradable materials

Grade 6 → Water and its properties ↓


Properties of water


Water is one of the most important substances on Earth. It covers about 71% of the Earth's surface and is essential for all living organisms. In our grade 6 chemistry lesson, we will explore the various properties of water, both physical and chemical, that make it unique and indispensable for life.

Composition of water

The chemical formula of water is represented as:

H 2 O

This means that each water molecule is made up of two hydrogen atoms and one oxygen atom. The unique structure of the water molecule contributes to its special properties.

In the water molecule, the oxygen atom is covalently bonded to hydrogen atoms. However, the electrons are not shared equally. This unequal sharing gives the oxygen atom a slightly negative charge and the hydrogen atom a slightly positive charge, making water a polar molecule.

Hey H H

Visual representation of a water molecule: The red circle represents the hydrogen atom and the blue circle represents the oxygen atom.

Physical properties of water

1. States of water

Water is unique because it naturally occurs in all three states of matter — solid, liquid, and gas:

  • Solid: When water freezes at 0°C, it turns into ice.
  • Liquid: Water is mostly found in a liquid state, from rivers to oceans.
  • Gas: When water boils at 100°C, it turns into steam or water vapor.

2. Boiling point and freezing point

Water has a high boiling point and a stable freezing point. This is due to the hydrogen bonds between water molecules. A large amount of heat is required to break these bonds:

  • Boiling point: 100°C or 212°F
  • Freezing point: 0°C or 32°F

Water's high boiling point affects weather and climate, because it keeps the temperature of lakes and oceans stable.

3. Density and expansion on solidification

Unlike most substances, water expands when it freezes. This is why ice floats on water. Water has a density of about 1g/cm³ in its liquid state, but it is less dense as ice:

When water freezes, the molecules arrange themselves into a crystal-like structure bound by hydrogen bonds, allowing them to take up more space. As a result, ice is about 9% less dense than water. This property is important for aquatic life during winter, as it means that only the surface of water bodies freezes, allowing life to continue below.

Chemical properties of water

1. Solvent abilities

Water is known as the "universal solvent" because it can dissolve more substances than any other liquid. This property is due to its polarity, which allows it to interact with a variety of ions and molecules:

  • Water can dissolve salts such as NaCl by surrounding each sodium and chloride ion, separating them from the solid lattice.
  • It also plays an important role in the transport of nutrients and waste products in living organisms by dissolving gases and other nutrients.

Surface tension

Water has a very high surface tension due to hydrogen bonds between its molecules. Surface tension allows some insects, such as water striders, to glide across the surface of water without sinking.

Surface tension

This high surface tension is the reason why water droplets form and accumulate on surfaces such as leaves.

Heat capacity

Water has a very high specific heat capacity, which means it can absorb a lot of heat without significantly increasing its temperature. This property helps regulate Earth's climate by absorbing heat during the day and releasing it at night.

Cohesion and adhesion

Hydrogen bonding causes water molecules to stick well to each other. This property is evident in the formation of water droplets on surfaces.

Water is also an adhesive substance because it can stick to other substances. An example of this is when water rises in a small tube via capillary action:

  • Cohesion: Water is attracted towards itself.
  • Adhesion: Water attracts other molecules.

Acid-base properties

Water can act as both an acid and a base, a concept described by the Bronsted-Lowry theory. However, pure water is neutral with a pH of 7. Water itself can ionize, as shown in the equilibrium reaction:

H 2 O (l) <-> H + (aq) + OH - (aq)

Water's ability to resist changes in pH makes it an excellent buffer and is important in many chemical reactions.

Conclusion

In short, water's unique properties make it essential to life and play a vital role in Earth's ecosystems. Understanding these properties helps us understand why water is so important to life, as well as its role in a variety of natural and man-made processes.


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Properties of water

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