Properties and Kinds of Water Lec 2

Properties and Kinds of Water (1) Humans live on a planet that is dominated by water 70 % of the Earth's surface is covered with it Hence, water is everywhere, from huge oceans to invisible water molecules making up water vapor in the air Freshwater is a primary resource for all...

Properties and Kinds of Water (1) Humans live on a planet that is dominated by water 70 % of the Earth's surface is covered with it Hence, water is everywhere, from huge oceans to invisible water molecules making up water vapor in the air Freshwater is a primary resource for all terrestrial life on this planet  Properties and Kinds of Water Humans live on a planet that is dominated by water Important for the facilitation of most biotic and abiotic environmental processes Humans use water for basic survival and require water for use in industry, agriculture, transportation, and electrical power generation We can see and feel the physical properties of water, but there are also many chemical, electrical, and atomic-scale properties of water that affect all life and substances on Earth. Properties and Kinds of Water WATER FACTS 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 Water freezes at 32° Fahrenheit (F) and boils at 212°F (at sea level, but 186.4° at 14,000 feet) Water is unusual in that the solid form, ice, is less dense than the liquid form, which is why ice floats WATER FACTS  Water is called the "universal solvent" because it dissolves more substances than any other liquid. This means that wherever water goes, either through the ground or through our bodies, it takes along valuable chemicals, minerals, and nutrients Pure water has a neutral pH of 7, which is neither acidic (less than 7) nor basic (greater than 7). WATER FACTS The water molecule is highly cohesive — it is very sticky, meaning water molecules stick to each other. Water is the most cohesive among the non-metallic liquids The water molecule is highly adhesive — it is very sticky, meaning water molecules tend to stick to molecules of other substances WATER FACTS Pure water, which you won't ever find in the natural environment, does not conduct electricity. Water becomes a conductor once it starts dissolving substances around it Water has a high heat index—it absorbs a lot of heat before it begins to get hot. This is why water is valuable to industries and in your car's radiator as a coolant WATER FACTS The high heat index of water also helps regulate the rate at which air changes temperature, which is why the temperature change between seasons is gradual rather than sudden, especially near the oceans The density of water means that sound moves through it long distances (ask a whale!). In sea water at 30°C, sound has a velocity of 1,545 meters per second (about 3,500 miles per hour) WATER FACTS 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 Surface tension is responsible for capillary action, which allows water (and its dissolved substances) to move through the roots of plants and through the tiny blood vessels in our bodies. WATER FACTS WATER FACTS WATER FACTS Air pressure affects the boiling point of water, which is why it takes longer to boil an egg at high altitude than at the beach. The higher the altitude, the lower the air pressure, the lower the boiling point of water, and thus, the longer time to hard-boil an egg. At sea level water boils at 212°F (100°C), while at 5,000 feet, water boils at 202.9°F (94.9 °C).  PHYSICAL PROPERTIES OF WATER 1. ADHESION AND COHESION Adhesion: Water is attracted to other substances Cohesion: Water is attracted to water Water properties that affect every water molecule on Earth and also the interaction of water molecules with molecules of other substances Cohesion and adhesion are the "stickiness" that water molecules have for each other and for other substances ADHESION AND COHESION  ADHESION AND COHESION A water drop is composed of water molecules that like to stick together-an example of the property of cohesion In the picture of pine needles, the water droplets are stuck to the end of the pine needles-an example of the property of adhesion Also noticeable in this picture is the effect that gravity has on the water drops Gravity is working against both adhesion and cohesion, trying to pull the water drop downward ADHESION AND COHESION  COHESION If you just look at the picture of the water drop sitting of the leaf, you might think the water drop has a "skin" holding it into a sort of flattened sphere It turns out that this surface tension is the result of the tendency of water molecules to attract one another The natural form of a water drop occurs during the "lowest energy state", the state where the atoms in the molecule are using the least amount of energy ADHESION AND COHESION  COHESION For water, this state happens when a water molecule is surrounded on all sides by other water molecules, which creates a sphere or ball (perfectly round if it was in outer space) On Earth, the effect of gravity flattens this ideal sphere into the drop shape we see Although you may have heard of a "skin" where water meets the air, this is not really an accurate description, as there is nothing other than water in the drop  COHESION The cohesive property of water creates attraction between particles of the same substance (why water is attracted to itself) The resulting effect of this attraction is surface tension (a measure of the strength of water’s surface) This is a result of the tendency of water molecules to attract to one another, or cohere, at the surface of any accumulation of water It produces a surface film on water that allows insects to walk on the surface of water COHESION ADHESION Adhesion is the attraction of water molecules to another substance Water is highly cohesive—it is the highest of the non- metallic liquids. Water is sticky and clumps together into drops because of its cohesive properties, but chemistry and electricity are involved at a more detailed level to make this possible  ADHESION More precisely, the positive and negative charges of the hydrogen and oxygen atoms that make up water molecules makes them attracted to each other If you've played with bar magnets you will know that the north pole of one magnet will repel the north pole of another magnet, but it will attract the south pole of another magnet Opposite magnetic poles attract one another much like positively charged atoms attract negatively charged atoms in water molecules.  ADHESION In other words, adhesion property of water allows it to make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton Example of this is the capillary action of water molecules that “tow” each other along when in a thin glass tube The transpiration process which plants and trees remove water from the soil, and paper towels soak up water. CAPILLARY ACTION Even if you've never heard of capillary action, it is still important in your life Capillary action is important for moving water (and all of the things that are dissolved in it) around It is defined as the movement of water within the spaces of a porous material due to the forces of adhesion, cohesion, and surface tension  CAPILLARY ACTION Capillary action occurs because water is sticky, thanks to the forces of cohesion (water molecules like to stay close together) and adhesion (water molecules are attracted and stick to other substances) Adhesion of water to the walls of a vessel will cause an upward force on the liquid at the edges and result in a meniscus which turns upward. The surface tension acts to hold the surface intact.  CAPILLARY ACTION Capillary action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules The height to which capillary action will take water in a uniform circular tube is limited by surface tension and, of course, gravity Not only does water tend to stick together in a drop, it sticks to glass, cloth, organic tissues, soil, and, luckily, to the fibers in a paper towel  CAPILLARY ACTION Dip a paper towel into a glass of water and the water will "climb" onto the paper towel In fact, it will keep going up the towel until the pull of gravity is too much for it to overcome It "magically" climb up the towel, appearing to ignore gravity. You are seeing capillary action in action, and "climbing up" is about right - the water molecules climb up the towel and drag other water molecules along.  CAPILLARY ACTION Plants and trees couldn't thrive without capillary action Plants put down roots into the soil which are capable of carrying water from the soil up into the plant Water, which contains dissolved nutrients, gets inside the roots and starts climbing up the plant tissue Capillary action helps bring water up into the roots. But capillary action can only "pull" water up a small distance, after which it cannot overcome gravity.  CAPILLARY ACTION To get to pull water up to all the branches and leaves, the forces of adhesion and cohesion go to work in the plant's xylem to move water to the furthest leaf Capillary action is also essential for the drainage of constantly produced tear fluid from the eye Two tiny-diameter tubes, the lacrimal ducts, are present in the inner corner of the eyelid; these ducts secrete tears into the eye  CAPILLARY ACTION Maybe you've used a fountain pen.... or maybe your parents or grandparents did. The ink moves from a reservoir in the body of the pen down to the tip and into the paper (which is composed of tiny paper fibers and air spaces between them), and not just turning into a blob Of course, gravity is responsible for the ink moving "downhill" to the pen tip, but capillary action is needed to keep the ink flowing onto the paper WATER MENISCUS A meniscus is a curve in the surface of a molecular substance (water, of course) when it touches another material With water, you can think of it as when water sticks to the inside of a glass WATER MENISCUS Why a meniscus occurs? Adhesion is responsible for a meniscus and this has to do in part with water's fairly high surface tension. Water molecules are attracted to the molecules in the wall of the glass beaker And since water molecules like to stick together, when the molecules touching the glass cling to it, other water molecules cling to the molecules touching the glass, forming the meniscus Why a meniscus occurs? . They'll travel up the glass as far as water's cohesive forces will allow them, until gravity prevents them from going further Cohesion is an intermolecular attraction between like molecules (other water molecules in this case).