Grade 7 Chemistry Chapter 3: Water and Atmosphere (PDF)

Chemistry Grade 7 Chapter three WATER AND ATMOSPHERE WATER Occurrence of Water in Nature Water (chemical formula: H2O) : is a transparent fluid and is the major constituent of the fluids of org...

Chemistry Grade 7 Chapter three WATER AND ATMOSPHERE WATER Occurrence of Water in Nature Water (chemical formula: H2O) : is a transparent fluid and is the major constituent of the fluids of organisms. As a chemical compound, a water molecule contains one oxygen and two hydrogen atoms. Water can exist in three physical states on Earth. 1- Liquid state such as lakes, oceans. 2 – Solid state such as snow, ice. 3- Gaseous state such as steam (water vapor) Q/ what is the major importance of water for living things? In some organisms, up to 90% of their body weight comes from water. Up to 60% of the human adult body and up to 50 % of some tissues of plants are water It can be found in the composition of many minerals rocks 87% of milk is water. Q/ What are the most important properties of water? 1. Pure water is transparent liquid, colorless, tasteless, and odorless 2. Pure water boils at 100°C and Freezes at 0°C under 1 atmosphere pressure. 3. Density of water is 1 cm3. 4- Pure water is poor conductor of electricity. 5. Water is a universal solvent. It is able to dissolve a large number of different substances such as table salt (NaCl), sugar (C6H12O6), oxygen (O2), carbon dioxide (CO2), and nitrogen (N2) etc. Explain / most solids sink in the liquid. Answer / The solid state of most substances is denser than the liquid state Explain / A ice floats in liquid water Answer / Answer /because ice is less than dense liquid water. Therefore many creatures can live under the surface of the frozen lake and sea. The Importance of Water for Our Bodies Water makes up more than two thirds of human body weight. The human brain is made up of 95% water; blood is 82% and lungs 90%. Dehydration: is a condition that results when the body loses more water than it takes in. The Structure of Water Water can be separated by using electricity and electrolysis machine. Q/Explain water analysis electrically. 1- Electrolysis cell filled with acidic water. After electric current passed through the solution. 2- Water can be separated by process analysis electrically into hydrogen and oxygen. Explain / in the water be volume of hydrogen gas is twice the volume of oxygen gas. Answer / because water molecule (H2O) contains two hydrogen atoms and one oxygen atom. In the water cycle water evaporates from oceans, lakes and rivers then falls as rain, snow, hail, dew and frost Humidity: is a measure of the amount of water vapor in the air compared with the maximum amount possible. Q/ what does this means: the humidity is 100%? Which means it cannot hold any more water (saturated) and it is raining or foggy. People feel most comfortable when the humidity is about 50%. How wind form? 1- The weather caused by the sun warming the earth and atmosphere. 2- A sea breeze blows from the sea towards the land. 3- The warm land heat the air just above it and this causes the air particles to move a part. 4- This, in turn, makes the air less dense and begins to rise. 5- Cool air from the sea that comes in to take the place of the rising air and form a circular current. This is a sea breeze. There are three ways in which clouds can form: 1- A mass of warm air drifting over the ocean towards a range of mountains. 2- Clouds can also form when one area of the earth heats up more than areas around it. 3- Clouds sometimes form when a large mass of cold air moves under a large mass of warm moist air pushing it up to where it is cooler this is called ( a cold front). (1) (2) (3) Tornadoes: are funnel-shaped clouds that sometimes form under severe thunderstorms. POLLUTION WATER: is the contamination of streams, lakes, seas, underground water or oceans by substances, which are harmful for living beings. Point source solution: 1- Trash Dumping. 2-Slug Dumping. 3- Oil Spills.