Solvents and solutions

Pure water and impure water Pure water contains no other substances mixed with it (dissolved or not dissolved). Water from rivers, lakes, and streams is suitable for human uses (fresh water). Sea water is not useful for human uses (salty water). Water available as fresh(rivers, streams and lakes) should be further purified.

Methods to purify water Mud and other insoluble substances can be removed from water by filtration or decantation. Micro organisms such as bacteria are killed by passing chlorine gas through water.

How to test water? Physical test: Water boils at 100 degree C Chemical tests: Water turns anhydrous (dry) white copper sulphate to blue crystals CuSO 4 + 5H 2 O  CuSO 4.5H 2 O (White powder) (Blue crystals) Water turns cobalt chloride paper from blue to pink

Solvents, solute and solution A solute is a substance which dissolves in a solvent to form a solution A solvent is the substance in which a solute dissolves to form a solution A mixture of solute and solvent is called a solution In salt solution, salt is the solute and water is the solvent

Types of solutions Unsaturated solution: if more solute can be dissolved in a solution at the given temperature. Saturated solution: if no more solute can be dissolved at the given temperature.

Solubility Some substances are more soluble in water than others. The amount of solute (in grams) dissolves in 100 g of solvent at a given temperature is called solubility of the substance. Solubility increases when we increase the temperature.

Hardness of water Hardness of water is caused by calcium and magnesium compounds dissolved in water. They are mainly hydrogen carbonate and sulphates of calcium and magnesium. If soap lathers easily, it means the water contains very little CALCIUM and MAGNESIUM compounds. It is SOFT WATER. A GREYISH SCUM and hardly any lather shows that MORE CALCIUM and MAGNESIUM is present. The water is called HARD WATER.

Hard and soft water SCUM-- Calcium and Magnesium compounds react with SOAP to give an INSOLUBLE product. EQUATION: Calcium Suphate + Sodium Stearate (soap)  Calcium Stearate (scum) + Sodium Sulphate Temporary HARD WATER contains lots of CALCIUM HYDROGENCARBONATE. On Heating, the compound breaks down to form CALCIUM CARBONATE (insoluble) and releases carbon dioxide gas. When Hydrogencarbonate is removed, water becomes SOFT WATER. Calcium hydrogen carbonate (HEAT)  calcium carbonate + carbon dioxide + water

Removing hardness Hardness caused by other compounds (sulphates of calcium and magnesium) is called PERMANENT HARDNESS. Permanent hardness is removed by ion exchange method. That is changing calcium ions into insoluble compounds. Example: Use washing soda (sodium carbonate, Na 2 CO 3 ) Calcium sulphate (soluble) + sodium carbonate (soluble)  sodium sulphate (soluble) + calcium carbonate (insoluble)

Ionic substances dissolve in water (salts) Organic and non-ionic compounds do not dissolve in water. They dissolve only in organic liquids. Detergents as suspension can remove ionic and non-ionic substances from objects. Detergents are simples molecular compounds in water. Ionic compounds dissolve in water and non-ionic compounds dissolve in molecular compounds (detergents)

Water pollution Water pollution is the contamination of water bodies(e.g. lakes, rivers, ocean and ground water). Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds. Domestic wastes, industrial wastes and use of fertilizers can cause water pollution

Composition of air

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