Air and Water — Important Questions

4°C

Step 1: Water shows unusual behavior when heated from 0°C - it actually contracts instead of expanding initially. Step 2: As temperature rises from 0°C to 4°C, water molecules come closer together, increasing density. Step 3: At 4°C, water occupies the least space and has maximum density of 1 g/cm³. Step 4: Above 4°C, water expands like other liquids and density decreases. Step 5: This property explains why ice floats on water and why lakes freeze from top to bottom, allowing aquatic life to survive in winter. At 0°C, water freezes and becomes less dense.

Barometer

Step 1: A barometer is specifically designed to measure atmospheric pressure. Step 2: It works by balancing the weight of air column against a column of mercury or using mechanical sensors. Step 3: Mercury barometers show pressure changes by the rise and fall of mercury in a tube. Step 4: Aneroid barometers use mechanical components that expand or contract with pressure changes. Step 5: Barometric readings help predict weather changes as pressure variations indicate weather patterns. Thermometer measures temperature, hygrometer measures humidity, and rain gauge measures rainfall.

Rain water

Step 1: Rain water is formed by evaporation of water from seas, rivers, and lakes due to solar heat. Step 2: During evaporation, only pure water molecules change to vapor, leaving behind all impurities and dissolved salts. Step 3: Water vapor rises high in the atmosphere and condenses to form clouds. Step 4: When water droplets fall as rain, they are essentially distilled water, free from most impurities. Step 5: However, rain water may collect some atmospheric pollutants while falling, but it's still the purest natural source. Sea water has high salt content, river and well water contain diss

Boiling

Step 1: Boiling water raises its temperature to 100°C, which is lethal to most bacteria and germs. Step 2: High temperature destroys the cell walls and proteins of harmful microorganisms. Step 3: Boiling for 10-15 minutes ensures complete sterilization of water. Step 4: After boiling and cooling, heavy impurities settle at bottom and dissolved salts may form scum on surface. Step 5: Boiled water can then be filtered to remove remaining physical impurities, making it safe for drinking. Filtration removes physical impurities but not bacteria, decantation and sedimentation only separate heavy par