Welcome to GattPrep!
👩🏽🏫 Introduction
Hello, young scientist! 👋🏽
Think for a moment—how many times have you used water today? Did you drink it? Bathe with it? Maybe you used it in cooking, or saw it flowing in a river nearby. Water seems simple, yet it’s an extraordinary substance with amazing properties that make life possible. Today, we’ll dive into understanding these incredible properties. By the end of this lesson, you’ll appreciate why water is so vital to every living thing, including you!
📘 Core Concepts
Physical properties are qualities we can observe or measure without changing water’s identity. Here are water’s key physical properties:
Pure water is a clear, colourless, odourless, and tasteless liquid.
It freezes at 0°C and boils at 100°C at normal atmospheric pressure (1 atmosphere).
It has a maximum density of 1 g/cm³ at 4°C.
It is a universal solvent, dissolving many substances easily due to its polar nature.
Chemical properties describe how water reacts with other substances. Some essential chemical properties include:
Water reacts with certain metals, forming metal hydroxides and releasing hydrogen gas.
2Na+2H2O→2NaOH+H2↑
It combines with non-metal oxides to produce acids.
CO2+H2O→H2CO3(Carbonic acid)
It participates in hydrolysis, breaking down certain salts into acidic or basic solutions.
👩🏽🔬 Real-Life Examples
Ice Floats: Ever wondered why ice floats on water? It’s because water expands when it freezes, becoming less dense. This unusual property allows aquatic life to survive beneath frozen lakes and ponds in winter.
Sweating to Cool Down: When we sweat, the water in sweat evaporates, removing heat and cooling our bodies. This happens due to water’s high latent heat of vaporization.
📐 Sample Problem Walkthrough
🧠 Problem: Explain why water pipes sometimes burst in very cold weather.
✅ Step-by-Step Solution:
Understand the property: Water expands when freezing due to hydrogen bonding between water molecules forming an open crystalline structure (ice).
Connect to scenario: When water freezes inside a pipe, it expands.
Result of expansion: Pressure increases until the pipe can’t withstand it, causing it to burst.
✔️ Answer: Water expands when it freezes, and this expansion increases the internal pressure, leading to bursting pipes in cold weather.
✍🏽 Practice Exercises
1. Fill in the blanks:
(a) Pure water boils at ______°C under normal atmospheric pressure.
(b) Water expands when it ______, making ice float.
✅ Answers:
(a) 100
(b) freezes
2. State True or False:
(a) Water is a good solvent because it is polar. (True)
(b) Water contracts and becomes denser when it freezes. (False)
✅ Explanations:
(a) True, water’s polar nature allows it to dissolve many substances.
(b) False, water expands upon freezing.
3. Short Answer:
Explain briefly why sweating cools your body.
✅ Sample Answer:
Sweating cools our body because the evaporation of water (sweat) from our skin removes heat, due to water’s high latent heat of vaporization.
🌀 Recap
Today we learned that:
Water has unique physical properties (clear, odourless, freezes at 0°C, boils at 100°C, universal solvent).
Water exhibits interesting chemical properties, like reacting with metals and non-metal oxides.
Real-world implications include floating ice and cooling via sweat evaporation.
💭 Reflection Prompt
Think about a situation in your daily life where water’s unique properties help you directly. Maybe it’s washing clothes, drinking tea, or watering plants. Identify and write down at least two specific water properties involved.
Discuss your answer with a classmate or note it down in your science journal!
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