Water

Water is essential for life and practical chemistry, but it often contains impurities that can impact its properties and use. This section covers the testing of water, assessing its purity, identifying harmful and beneficial substances, and understanding how domestic water is treated for safe consumption.

Testing for the presence of water

1. Chemical Tests for Water

   • Anhydrous Cobalt(II) Chloride:

     • Blue → pink in the presence of water.

     • Example: Used in desiccants to detect moisture.

   • Anhydrous Copper(II) Sulfate:

     • White → blue when water is added.

     • Example: Often used in experiments to test for water in hydrates.

2. Testing Water Purity

   • Melting Point: Pure water freezes at exactly 0°C.

   • Boiling Point: Pure water boils at exactly 100°C at standard atmospheric pressure.

   • Impurities cause deviations in these points (e.g., salt lowers the freezing point).

Why use distilled water in Chemistry?

• Distilled Water: Free from most chemical impurities, ensuring accurate experimental results.

• Tap Water: Contains dissolved minerals and other impurities that may interfere with reactions.

Natural water sources and impurities

Substances Found in Natural Water

1. Beneficial Substances:

   • Dissolved Oxygen: Essential for aquatic life.

   • Metal Compounds: Provide essential minerals for organisms.

2. Potentially Harmful Substances:

   • Toxic Metal Compounds: Can harm health.

   • Plastics: Harm aquatic life and ecosystems.

   • Sewage: Contains harmful microbes that cause disease.

   • Nitrates and Phosphates: Found in fertilizers and detergents, causing deoxygenation of water and harming aquatic life (eutrophication).

Treatment of domestic water supplies

Steps in Water Treatment

1. Sedimentation: Large solids settle at the bottom of tanks.

2. Filtration: Removes smaller solid particles.

   • Example: Sand filters are commonly used.

3. Activated Carbon Treatment: Removes unwanted tastes and odors.

4. Chlorination: Kills harmful microbes to make water safe for drinking.

Results in water that is free from bacteria but contains some soluble substances, including chlorine compounds.

Filtration treatment of domestic water