Water exists in three states: solid (ice), liquid (water), and gas (steam). – Solid: At temperatures below 0°C, water freezes to form ice. – Liquid: Between 0°C and 100°C, water remains in a liquid state. – Gas: Above 100°C, water boils and converts to steam.

Water is considered a compound because it is made up of two hydrogen atoms and one oxygen atom, chemically bonded together in a fixed ratio of 2:1, forming the molecule \(H_2O\).

Mumbai and Chennai are coastal cities, and the presence of the sea moderates their temperatures, preventing them from falling as low as in Delhi, which is an inland city.

Water has a high specific heat capacity, meaning it can absorb and retain a large amount of heat without a significant increase in temperature. This property helps in regulating the temperature of our body.

Water is known as a universal solvent because it can dissolve more substances than any other liquid. This is due to its polar nature and ability to form hydrogen bonds with other molecules.

Torrential rain is associated with strong winds and heavy rainfall, which can cause flooding, landslides, and destruction of property, leading to violent and dangerous conditions.

Water’s high specific heat capacity allows it to absorb and release large amounts of heat, which helps to moderate the climate by stabilizing temperatures in coastal regions.

The density of water is highest at 4°C. This property causes water to stratify in lakes and oceans, with the densest water sinking to the bottom. This affects aquatic life and the mixing of nutrients in the water bodies.

– Melting point: 0°C
– Boiling point: 100°C
– Specific heat capacity: \(4.18 \, \text{J/g°C}\)
– Specific latent heat of fusion: \(334 \, \text{J/g}\)
– Specific latent heat of vaporization: \(2260 \, \text{J/g}\)

When the pond gets covered with thick ice, the water below the ice remains at 4°C, which is the densest and warmest layer. This allows fishes and aquatic animals to survive in the liquid water beneath the ice.

Water is made up of hydrogen and oxygen, both of which are gases at room temperature. However, when they combine to form water, it is a liquid at room temperature. The chemical properties of water are entirely different from its constituent elements.

Since water has maximum density at 4°C, during winter, the colder water (below 4°C) rises to the top and freezes, while the 4°C water stays at the bottom, allowing aquatic life to survive in the relatively warmer water.

(a) Tap water contains dissolved salts:
– Take a sample of tap water and boil it until all the water evaporates. The residue left behind indicates the presence of dissolved salts.
(b) Tap water contains dissolved gases:
– Take a sample of tap water and heat it gently. Bubbles will form before the water boils, indicating the presence of dissolved gases.

The solubility of \(CO_2\) in water is important for aquatic plants to perform photosynthesis. The solubility of \(O_2\) is crucial for the respiration of aquatic animals.

Air dissolved in water contains a higher proportion of oxygen compared to ordinary air, which is essential for the respiration of aquatic life.

Rivers and lakes do not freeze easily because of the high specific heat capacity of water and the release of latent heat during the freezing process, which helps to maintain the temperature above freezing point for longer periods.

Dissolved salts in water are essential for the survival of aquatic life as they provide necessary minerals and help maintain osmotic balance in organisms.

(a) Boiled or distilled water tastes flat:
– Boiled or distilled water tastes flat because it lacks dissolved gases and minerals that contribute to the taste of regular water.
(b) Ice at zero degree centigrade has greater cooling effect than water at 0°C:
– Ice at 0°C absorbs latent heat as it melts, providing a greater cooling effect compared to water at the same temperature.
(c) Burns caused by steam are more severe than burns caused by boiling water:
– Steam contains more energy due to the latent heat of vaporization, making steam burns more severe than burns from boiling water.
(d) Rain water does not leave behind concentric rings when boiled:
– Rainwater is relatively pure and contains fewer dissolved solids compared to tap water, which leaves behind concentric rings when boiled.
(e) Air dissolved in water contains a higher proportion of oxygen:
– The proportion of oxygen is higher in water to support aquatic life.
(f) If distilled water is kept in a sealed bottle for a long time, it leaves etchings on the surface of the glass:
– Distilled water is more reactive and can dissolve silica from the glass over time, leaving etchings on the surface.

The diagram illustrates the phase changes of water and the associated latent heats: – Latent heat of fusion: Energy required to change from solid to liquid (or released from liquid to solid). – Latent heat of vaporization: Energy required to change from liquid to gas (or released from gas to liquid). – Latent heat of solidification: Same as latent heat of fusion but in the reverse process. – Latent heat of condensation: Same as latent heat of vaporization but in the reverse process.