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 → Water and its importance ↓


Hard and soft water


Water is essential for all life on Earth. It is used for drinking, cooking, cleaning and in many industrial processes. But have you ever wondered why some water feels different from others? The answer lies in the difference between hard and soft water. Here, we will explore what hard and soft water are, their differences and their importance in our daily lives.

What is water?

Water is a chemical compound consisting of two hydrogen atoms and one oxygen atom. It is written in chemistry as: H 2O. About 71% of the Earth's surface is covered with water, mainly in oceans, rivers and lakes. It is vital for sustaining life, as it is involved in many biological processes.

Hard water vs soft water

The terms "hard water" and "soft water" describe the mineral content in water. These terms are important because they affect how water interacts with soaps and detergents, as well as its effect on appliances and plumbing.

Hard water

Hard water is water that contains high concentrations of minerals, particularly calcium (Ca 2+) and magnesium (Mg 2+) ions. These minerals are usually picked up by water as it moves through rocks and soil.

Here's a simple example to help you understand hard water:

Water passing through limestone (which contains calcium) becomes hard because the calcium in it gets dissolved:
  Limestone (calcium carbonate: CaCO 3 ) + Water + Carbon dioxide (CO 2 ) →
  Calcium Bicarbonate (Ca(HCO 3 ) 2)

Soft water

Soft water, on the other hand, has little or no calcium or magnesium ions. It may have some other ions, but it does not contain the ions that make water "hard." Rainwater is naturally soft.

How to test water hardness

You can often test water hardness using ordinary soap. Here's a fun water testing activity:

  • Fill a bottle halfway with water.
  • Add a few drops of liquid soap.
  • Close the lid of the bottle and shake well.

If the water forms lots of bubbles, it's probably soft. If it doesn't form bubbles and scum comes out easily, it's probably hard.

Effects of hard water

Hard water can have many effects on our daily lives:

  • Soap efficiency: In hard water, soap reacts with calcium and magnesium to form lather, making cleaning and washing more difficult.
  • Appliance life: Hard water can cause mineral deposits to form in pipes and appliances such as kettles and washing machines. This can reduce efficiency and lifespan.
  • Skin and hair: Some people find that hard water causes their skin to become dry and hair to become brittle.

Why is water harder in some areas?

The hardness of water in an area depends largely on the geological features. In areas where water flows through limestone or chalk, it is harder due to the higher amount of calcium carbonate.

hard water area Minerals Water source

Benefits of hard water

Although hard water may cause some discomforts, it also provides benefits:

  • Nutrition: Hard water can provide essential minerals such as calcium and magnesium, which are important for health.
  • Taste: Some people prefer the taste of hard water over soft water because the minerals can impart a taste.

How can hard water be made soft?

There are several ways to soften hard water, including:

  • Ion exchange: In this method calcium and magnesium ions are replaced with sodium or potassium ions to soften the water.
  • Lime softening: Chemicals are added to remove hardness by drawing out calcium and magnesium from the water.
  • Reverse osmosis: Water is filtered through a semi-permeable membrane that removes hard minerals.

Here is an example of ion exchange softening:

Calcium ions: Ca 2+ + resin (Na)
Exchange: Na + and Ca 2+ removed on resin

Effects and considerations of soft water

Although soft water can be beneficial, especially for cleaning and appliance longevity, there are a few other considerations:

  • Mineral deficiencies: Soft water is deficient in calcium and magnesium. This may mean relying on diet or supplements for these nutrients.
  • Sodium content: Water softened using sodium-based ion exchange may contain increased sodium levels, which may be a concern for people on a low-sodium diet.

Conclusion

Understanding the difference between hard and soft water is important for both practical and health reasons. Each type of water has its own advantages and disadvantages. By knowing about water hardness, we can make informed decisions about how to treat it and ensure it suits our needs.

Interactive understanding

Remember, you can always perform your own simple tests to determine water hardness at home or in a school lab. Using soap, observing the behavior of water, or using a water testing kit can be a fun experiment to better understand the science behind water chemistry.


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