Class 10 Chemistry Chapter 7 Notes

Complete Notes of Chapter No. 15: Water Class 10 or class 10 chemistry chapter 7 notes  by Mr. Tasneem Haider. These computerized notes are very helpful in the preparation of class 10 chemistry chapter 7 notes for students of the 10th class Chemistry and these are according to the paper patterns of all Punjab boards.

• Important Multiple Choice Questions (MCQs) of Chapter No. 15: Water for Chemistry Urdu Medium 10th Class.
• Important Short Questions of Chapter No. 15: Water for Chemistry Urdu Medium 10th Class
• Introduction: Throughout history, importance and significance of water has been recognized by mankind. Its importance is because of two reasons. First, it is an essential and major component of each and every living cell. For example, human body consists of about 70% water. Secondly, it provides an environment for animals and plants that live in water.
• So, all living organisms owe their life to water. Students Learning Outcomes We use water in daily life for drinking, cooking and washing purposes. Quality of drinking water has remained a major factor in determining human health and welfare since ages.
• Since World War II, there has been a rapid production and use of synthetic chemicals. Many of these chemicals (fertilizers and pesticides run off from agriculture lands and industrial discharge from industrial units) have polluted water supplies. Besides this, there is also a threat to groundwater from waste chemical dumps and landfills.
• Occurrence of Water: The oceans contain about 97% of world’s water. The rest of the water is in the form of glaciers, ice caps, groundwater and inland water (rivers, lakes, streams). It is also present in atmosphere in the form of water vapours. Sea water is unfit for drinking and agricultural purposes due to high percentage of dissolved salts. Only 0.2% of the total water on the Earth is potable, i.e. fit for drinking purposes.
• Water is composed of two elements: oxygen and hydrogen. One atom of oxygen combines with two atoms of hydrogen to form one molecule of water. Pure water is a clear, colourless, odourless and tasteless liquid with following properties:
• 1. It is neutral to litmus. 2. Its freezing point is 0°C and boiling point is 100 °C at sea level. 3. Its maximum density is 1 gcm-3 at 4°C. 4. It is excellent solvent for ionic as well as molecular compounds. 5. It has unusually high heat capacity about 4.2 Jg-1K-1, which is about six times greater than that of rocks. This specific property of water is responsible for keeping the Earth’s temperature within limits. Otherwise, day time temperature would have been too high to bear and night time temperature would have been too low to freeze everything.
• Water is the universal solvent because it can dissolve almost all the minerals. Its ability to dissolve substances is because of two unique properties of water:
• (i) Polarity of water molecule; (ii) Exceptional hydrogen bonding ability.
• Polar nature of water: Water molecule has polar structure, i.e. one end of the molecule is partially positive while the other end is partially negative because of electronegativity difference between oxygen and hydrogen atoms. All other polar substances are soluble in water, because the positive end of the substance is attracted by the negative end (Od-) of the water and negative end of the substance is attracted by the positive end (Hd+) of the water. The electrostatic attractions among the ions are overcome by the ion-dipole forces of attraction between ion and water molecules.
• Extensive hydrogen bonding ability: Water molecule is composed of oxygen and hydrogen atoms. Because of two O—H bonds and two lone pairs, one H2O molecule can form hydrogen bonding with four other H2O molecules, which are arranged tetrahedrally around the H2O molecule. This unique behaviour of water enables it to dissolve many polar non-ionic compounds having hydroxyl group (-OH), like alcohols, organic acids, glucose, sugar, etc. by forming hydrogen bonds with them.