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Home , Water of crystallization

Water Why is considered a compound? Water is a considered a compound, as it is a combination of two hydrogen atoms and one oxygen atom. Water is also considered an amphoteric, meaning it acts both as an acid and a base as it produces H+ and OH- by self-ionization. As a , its properties are: 1. In a water , hydrogen and oxygen are combined in a fixed ratio by mass (1:8). 2. Components cannot be separated by physical means. 3. It has a definite and constant composition. 4. It has definite and constant melting point, boiling point, freezing point and density. 5. Water can react with metals to form the corresponding hydroxides. The ease with which the reaction occurs depends on the position of the metal in the reactivity series. Why is water called a universal ? Water is called the universal solvent since it is capable of dissolving a variety of different substances more than any other liquid. Water can dissolve more substances than any other compound because of its polar nature. The water because of their composition – hydrogen with a positive charge on one side and oxygen with a negative charge on another, are able to attract other molecules easily. Water of : When of certain are formed, they do so with a definite number of molecules of water that are chemically combined in a definite proportion. Water of crystallization is defined as the number of water molecules, chemically combined in a definite molecular proportion, with the in its crystalline state. This water is responsible for the geometric shape and colour of the crystals. : A substance containing water of crystallization is called a hydrous substance or a hydrate. This water can be expelled, by heating, and then the salt is said to have become anhydrous. Examples of hydrated salts include:

1. 퐶푢푆푂45퐻2푂 (copper sulphate) 2. 퐹퐸푆푂47퐻2푂(ferrous sulphate) 3. 푁푎2퐶푂310퐻2푂()

Examples of : -

Examples of hydrates are (commonly used in the manufacturing of wallboard, cement and plaster of Paris), (used in many cosmetic, cleaning and laundry products). Hydrates are often used in skin care products to infuse moisture into the body. The world contains many gas hydrates, crystalline solids in which gas molecules are enclosed in structures made of water molecules. These form from very low temperatures and high pressure. They are mixed with sediment and found primarily deep in the ocean and in Arctic regions. Anhydrous compounds: An anhydrous compound (an anhydrate) is a compound with no water in its structure. After water is removed from a hydrate, it becomes an anhydrate. The water molecules are removed by suction or heating the compound to a high temperature. For example, an anhydrous salt has had water driven out from its crystals. Note: - An anhydrous compound from a hydrate is generally highly soluble in water, and when dissolved in water it will be a similar colour to that of the original hydrate, even if it changed colour transforming from the hydrate to the anhydrous compound. Examples of Anhydrates: - Anhydrates, also known as desiccants, remove water, so are often used in drying agents, such as paper products. Silica gel is one of the most commonly used anhydrates. A packet of silica gel is kept inside finished purses and other products to absorb water, keeping the surrounding area dry and preventing the growth of molds. Anhydrates can also retain moisture in food and tobacco products when they are in humectant form. Physical : - Property Value/ Behaviour of water Characteristic Colour Colourless Water bodies appear blue due to scattering of light. Odour Odourless Taste Tasteless Taste of water may be due to dissolved salts. Melting point 0°C under normal ↑ Pressure, ↓ Melting point pressure Boiling point 100°C at normal ↑ Pressure, ↑ Boiling point (Water boils at lower pressure temperatures at high altitudes where pressure is low.) Solvent High solvent Its polar nature makes water a universal solvent. properties, high dielectric constant Conduction Non-conductor in When salts are dissolved, water forms ions and pure form conducts electricity.

Chemical Properties of water: - Sodium and potassium  React violently with cold water.  Highly exothermic reaction.  Released hydrogen immediately catches fire. K + H2O → 2KOH + H2↑ + heat Na + H2O → 2NaOH + H2↑ + heat Calcium  Less violent reaction with water, the heat evolved is not enough for H2 to catch fire. Ca + 2H2O → Ca (OH)2 + H2↑ Ca starts floating as bubbles of H2 stick to metal surface

Magnesium  Reacts with hot water, starts floating due to 퐻2 bubbles sticking to it. Mg + 2H2O → Mg (OH)2 + H2↑ Aluminium, Zinc, Iron  React with steam to form oxide and hydrogen (reversible reaction 2Al + 3H2O → Al2O3 + 3H2↑ with steam) Zn + H2O → ZnO + H2 3Fe + 4H2O ↔ Fe3O4 + 4H2↑ Copper,  No reaction with water Gold, Platinum

What does drinking water contain? By its own nature, pure water is as tasteless and odourless, although it becomes contaminated easily because of its high . Water can acquire a taste, odour and colour because of the following reasons: 1. Water in nature is generally mixed with different minerals from different sources such as earth, industrial effluents, animal and plant matter etc., making it salty or putrid. 2. Drinking or potable water is infused with many substances to make it safe for drinking and other uses giving it a particular taste. Water contains air and salts in dissolved states: - 1. Importance of dissolved salts: a. Supply all living organisms (most importantly plants) with nutrients, minerals. b. Add taste to water. 2. Importance of dissolved air & Marine life depends on: a. Dissolved oxygen for breathing. b. Dissolved carbon dioxide for photosynthesis and shell formation. Solutions: - The following are the definitions of terms that are commonly used with respect to solutions and solubility: Solute: The substance that dissolves to form a solution.

Solvent: The substance in which a solute dissolve. Solution: The fluid formed when the solute dissolves in a solution. Saturated solution: When a solution cannot dissolve any more of the given solute at that temperature, it is called saturated solution. Unsaturated Solution: A solution which contains less amount of solute than is required to saturate it at that temperature. Supersaturated Solution: A solution that is more concentrated than a saturated solution is known as a super saturated solution. If a of a solute is added to this solution, the excess solute crystallizes. Concentration of a Solution: Is the amount of solute dissolved in a given amount of solvent. It is expressed as: 푀푎푠푠 표푓 푠표푙푢푡푒 1. Mass percent = x 100 % 푚푎푠푠 표푓 푠표푙푢푡푖표푛 (푠표푙푣푒푛푡 + 푠표푙푢푡푒) 푉표푙푢푚푒 표푓 푠표푙푢푡푒 2. Volume percent = x 100 % 푣표푙푢푚푒 표푓 푠표푙푢푡푖표푛 (푠표푙푣푒푛푡 + 푠표푙푢푡푒) Solubility: - It is the property of a solid, liquid or gaseous called as the solute to dissolve in a solid, liquid, or a gaseous substance called solvent. In simple words, solubility is the quantity of a particular substance that can dissolve in a particular solvent to give a saturated solution. The solubility of a substance depends on factors such as physical and chemical properties of the solute and solvent, temperature, pressure and the pH of the solution. Soft water and Hard water: - Hard water: The water that we call ‘hard’ is actually water that has high mineral content. When water percolates through deposits of chalk and limestone that are made up of magnesium carbonates and calcium, hard water is formed. Advantages of hard water: 1. It is rich in essential minerals 2. It is suitable for everyday drinking. 3. Useful for fighting and preventing certain heart and cardiovascular diseases 4. Better taste (than the one you will get while drinking soft water) Disadvantages of hard water: 1. Dishes with spots 2. Clothes that are dingy looking 3. Dry skin 4. Reduces the efficiency of household appliances Soft water:

We use the term ‘soft water’ to indicate water that has low concentrations of ions, in particular ions of magnesium and calcium. Such water naturally occurs where the drainage basin of rivers is formed of impervious, hard, calcium-poor rocks. Advantages of Soft Water: 1. Clean dishes 2. Soft skin 3. Prolonged life of water heaters, washing machines, dishwashers, etc. 4. Low energy bills Disadvantages of Soft Water: 1. Not suitable for drinking 2. May cause heart or circulatory problems 3. It can harm blood cells and interfere with the process in which oxygen is carried to our organs.