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Water - Causes of Water Pollution and Conservation

Grade 6ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Water is a chemical compound represented by the formula H2OH_2O, consisting of two atoms of Hydrogen and one atom of Oxygen.

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Water is known as the 'Universal Solvent' because it can dissolve more substances than any other liquid, which also makes it easy to pollute.

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Water Pollution is the contamination of water bodies like lakes, rivers, and oceans by harmful substances such as domestic sewage, industrial waste, and agricultural runoff (e.g., fertilizers containing KNO3KNO_3 and pesticides).

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Eutrophication is the process where water bodies receive excess nutrients, specifically Nitrates (NO3−NO_3^-) and Phosphates (PO43−PO_4^{3-}), leading to excessive growth of algae and depletion of dissolved oxygen (O2O_2).

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Industrial effluents often contain toxic heavy metals such as Lead (PbPb), Mercury (HgHg), and Cadmium (CdCd), which are harmful to aquatic life and humans.

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Potable water is water that is safe for drinking, free from harmful pathogens and chemical contaminants.

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Water Conservation methods include Rainwater Harvesting, which involves collecting and storing rainwater for future use, and the '3 Rs': Reduce, Reuse, and Recycle.

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Physical constants of water include a freezing point of 0∘C0^\circ C and a boiling point of 100∘C100^\circ C at standard atmospheric pressure.

📐Formulae

H2OH_2O

Density of water=1 g/cm3 at 4∘C\text{Density of water} = 1\text{ g/cm}^3 \text{ at } 4^\circ C

Boiling Point=100∘C\text{Boiling Point} = 100^\circ C

Freezing Point=0∘C\text{Freezing Point} = 0^\circ C

💡Examples

Problem 1:

Explain why fertilizers like Ammonium Nitrate (NH4NO3NH_4NO_3) are considered water pollutants when they wash into ponds.

Solution:

Fertilizers containing NH4NO3NH_4NO_3 provide excess nitrogen to the water body.

Explanation:

This leads to Eutrophication. The NO3−NO_3^- ions promote rapid algal growth (algal bloom). When these algae die, bacteria decompose them using up the dissolved O2O_2 in the water, which causes aquatic animals like fish to suffocate and die.

Problem 2:

A sample of water from a factory is found to contain HgHg. Identify the element and its effect.

Solution:

HgHg stands for Mercury, a toxic heavy metal.

Explanation:

Mercury (HgHg) causes water pollution. When consumed through the food chain (bioaccumulation), it can lead to serious neurological disorders in humans and animals.

Problem 3:

Calculate the state of water at −5∘C-5^\circ C and 110∘C110^\circ C.

Solution:

At −5∘C-5^\circ C, water is solid (Ice); at 110∘C110^\circ C, water is gas (Steam/Water Vapor).

Explanation:

Since the freezing point is 0∘C0^\circ C, any temperature T<0∘CT < 0^\circ C results in ice. Since the boiling point is 100∘C100^\circ C, any temperature T>100∘CT > 100^\circ C results in gaseous water.

Causes of Water Pollution and Conservation Revision - Class 6 Science ICSE