Water
Chapter Name : Hydrogen |
Sub Topic Code : 102_11_09_06_01 |
Topic Name : Water |
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Sub Topic Name : Physical Properties |
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Introduction
Water is a chemical compound with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at standard ambient temperature and pressure, but it often co-exists on Earth with its solid state, ice, and gaseous state (water vapor or steam). Water also exists in a liquid crystal state near hydrophilic surfaces.
Pre-Requisites:
Hydrogen bonding, Surface tension, Adhesion and Cohesion
Activity:
Most of these hydrides are good conductors of electricity in solid state.
Real Life Question:
Why water is so important for the living organisms?
Key Words / FlashCards
| Key Words | Definitions (pref. in our own words) |
|---|---|
| Hydrogen bonding | A hydrogen bond is the electromagnetic attractive interaction of a polar hydrogen atom in a molecule or chemical group and an electronegative atom, such as nitrogen, oxygen or fluorine, from another molecule or chemical group. |
| Surface tension | Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force. |
| Adhesion | Water is attracted to other substance. |
| Cohesion | Water is attracted to water. |
Learning aids / Gadgets
| Gadgets | How it can be used |
|---|---|
| pH paper | A pH indicator is a halo chromic chemical compound that is added in small amounts to a solution so that the pH (acidity or basicity) of the solution can be determined visually. • Pure water has a neutral pH of 7, which is neither acidic (<7) nor basic (>7). |
Real life uses :
The most important use of water in agriculture is for irrigation, which is a key component to produce enough food. Irrigation takes up to 90% of water withdrawn in some developing countries and significant proportions in more economically developed countries (United States, 30% of freshwater usage is for irrigation).
Places to visit :
Chemistry lab.
Practical examples around us
| Examples | Explainations |
|---|---|
| Water as a coolant | Water has a high specific heat index - it absorbs a lot of heat before it begins to get hot. This is why water is valuable to industries and in car's radiator as a coolant. |
What you learn in Theory:
• Water freezes at 32° Fahrenheit (F) and boils at 212°F. • Water is unique in that it is the only natural substance that is found in all three physical states—liquid, solid, and gas—at the temperatures normally found on Earth.
What you learn in Practice:
• Water has a very high surface tension. In other words, water is sticky and elastic, and tends to clump together in drops rather than spread out in a thin film, like rubbing alcohol.