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Water—The Essence of Life - Sources and Forms of Water

Grade 5CBSE

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

🔑Concepts

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Water is an essential natural resource for all living organisms. The chemical formula for a water molecule is H2OH_2O.

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Water exists in three states: Solid (ice), Liquid (water), and Gas (water vapor). These states are interchangeable by changing the temperature.

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The process of water changing from a liquid to a gas due to heating is called evaporation. The process of water vapor changing back into liquid upon cooling is called condensation.

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The freezing point of water, where it turns from liquid to solid, is 0∘C0^\circ C. The boiling point, where it turns from liquid to gas, is 100∘C100^\circ C.

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Sources of water are classified into Surface Water (rivers, lakes, ponds, and oceans) and Groundwater (water trapped beneath the Earth's surface).

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Rain is the primary source of fresh water on Earth. Only about 3%3\% of the Earth's water is fresh water, while approximately 97%97\% is saline (salty) water found in oceans.

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The Water Cycle is the continuous movement of water from the Earth's surface to the atmosphere and back through processes like evaporation, transpiration, condensation, and precipitation.

📐Formulae

H2OH_2O

Freezing Point=0∘CFreezing\ Point = 0^\circ C

Boiling Point=100∘CBoiling\ Point = 100^\circ C

Fresh Water+Saline Water=Total Water (100%)Fresh\ Water + Saline\ Water = Total\ Water\ (100\%)

💡Examples

Problem 1:

If a sample of water is cooled from 25∘C25^\circ C to 0∘C0^\circ C, what physical change occurs?

Solution:

The water will change from a liquid state to a solid state (ice).

Explanation:

Since 0∘C0^\circ C is the freezing point of water, the liquid loses heat energy and turns into its solid form.

Problem 2:

If the total water on Earth is 100100 parts and 9797 parts are in the oceans, calculate the amount of fresh water available using subtraction.

Solution:

100−97=3100 - 97 = 3 parts

Explanation:

To find the fresh water, we subtract the saline water (ocean water) from the total water using the following vertical calculation: 100−973\begin{array}{r} 100 \\ - 97 \\ \hline 3 \end{array}