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 → Solutions and Solubility ↓


Concentration of solutions


In chemistry, a solution is a type of mixture in which one substance dissolves in another. The substance being dissolved is called the solute, and the substance being dissolved is called the solvent. Together, they form a homogeneous mixture, which means it has a uniform appearance and composition.

What is concentration?

The concentration of a solution tells us how much solute is present in a given amount of solvent or solution. Understanding concentration is important because it helps us know how strong or weak a solution is. For example, in everyday life, you may be concerned about the concentration of sugar in your coffee or the concentration of salt in your soup.

Why is concentration important?

Concentrations are important in a variety of fields. In medicine, correct concentrations of drugs are necessary to ensure they are effective and safe. In environmental science, the concentrations of pollutants in air or water help determine whether they pose a threat to humans and wildlife. Even in cooking, knowing the concentrations of ingredients can affect the taste and texture of food!

Ways to express concentration

There are several ways to express concentration:

  • Mass percent: The mass of the solute divided by the total mass of the solution multiplied by 100.
  • Volume percent: The volume of solute divided by the total volume of the solution multiplied by 100.
  • Molarity (M): Moles of solute divided by liters of solution.
  • Molality (m): The number obtained by dividing the moles of solute by the kilograms of solvent.

Mass percent

The formula for mass percent is:

Mass Percent = (Mass of Solute / Mass of Solution) × 100

For example, if you dissolve 10 g of salt in 90 g of water, the mass of the solution will be 100 g. The mass percentage of salt in this solution is:

Mass Percent = (10 g / 100 g) × 100 = 10%

Volume percent

Volume percent is used when both the solute and the solution are liquids. The formula for volume percent is:

Volume Percent = (Volume of Solute / Volume of Solution) × 100

For example, if you have 30 ml of ethanol in 70 ml of water, the volume of the solution will be 100 ml. The volume percent of ethanol is:

Volume Percent = (30 mL / 100 mL) × 100 = 30%

Molarity

Molarity is one of the most common ways to express concentration in chemistry. The formula for molarity is:

Molarity (M) = Moles of Solute / Liters of Solution

For example, suppose you dissolve 1 mole of sodium chloride (NaCl) in 1 liter of water. The molarity of this solution is:

M = 1 mole / 1 L = 1 M

Molality

Molality is a measure of concentration that is not affected by temperature changes. The formula for molality is:

Molality (m) = Moles of Solute / Kilograms of Solvent

For example, if you dissolve 1 mole of sugar in 1 kilogram of water, the molality of the sugar solution will be:

m = 1 mole / 1 kg = 1 m

Visualization of concentration

Let us visualize concentration with some examples.

high concentration Medium concentrations Low concentrations

In the example above, each column represents a different level of concentration. The blue column represents a high concentration of solute, purple represents medium concentration, and red represents low concentration. The more solute there is, the higher the column, indicating a more concentrated solution.

Practicing with examples

Let's look at some more examples to strengthen our understanding.

Example 1: Lemonade

Imagine you are making lemonade. You have a cup of water and you add two teaspoons of sugar. How would you think about the concentration of sugar in your lemonade? Sugar is the solute, water is the solvent, and the two combine to form a solution. If you add more sugar, the lemonade becomes more concentrated.

diluted lemonade Thick lemonade

In the example above, the yellow circle represents thinner lemonade with less sugar, while the darker orange circle represents thicker lemonade with more sugar.

Example 2: Salt water

Suppose we have two beakers filled with water. In the first beaker we dissolve one teaspoon of salt. In the second beaker we dissolve five teaspoons of salt. In which beaker is the salt solution more concentrated?

1 teaspoon salt 5 teaspoons salt

The first beaker (light blue) contains the dilute solution, while the second beaker (dark blue) contains a more concentrated solution because of the higher amount of solute.

Daily applications of concentration

Understanding concentration helps us in day-to-day tasks. Here are some applications:

  • Cooking: Recipes often require precise concentrations of ingredients, such as sugar in a cake or vinegar in a salad dressing.
  • Cleaning: Cleaning solutions are often concentrated to remove tough stains.
  • Therapy: Doses of medications depend on precise concentrations to ensure that they are both safe and effective.
  • Environmental science: The concentration of pollutants helps assess the potential damage to an ecosystem.

Factors affecting solubility and concentration

Solubility is how well a solute can dissolve in a solvent at a given temperature. This is affected by concentration. Here are some factors that affect solubility:

  • Temperature: Most solids dissolve better in warm solvents. However, gases dissolve better in cold solvents.
  • Pressure: This mainly affects gases. At higher pressures, more gas can dissolve in a liquid.
  • Nature of solute and solvent: Some solutes dissolve better in certain solvents. For example, sugar dissolves well in water but not in oil.

Temperature and solubility

Let's use a solution of sugar and water to explain how temperature affects solubility.

Cold water Room temperature Hot water

In the figure above, each column shows how much sugar dissolves in different temperatures of water. Cold water (light green) dissolves the least amount of sugar, while hot water (dark green) dissolves the most sugar.

Conclusion

The concentration of solutions is a fundamental concept in chemistry that is widespread and also very useful in everyday life. Concentration gives us valuable information about the composition of solutions and affects their properties and uses. From simple tasks like flavoring food to complex industrial processes, concentration plays an important role.


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Factors Affecting Solubility
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Concentration of solutions

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