Properties of Water
What's so special about water?
When compared to almost all other substances on Earth, water is very special. This is because of water's molecular structure.
Polarity - Water's molecular structure causes it to have a polarity, which means that different parts of the molecule have different charges. The oxygen atom in a water molecule has more protons than the hydrogen atoms. Because of this, the electrons in the molecule are attracted to the positive charges and cluster closer to the oxygen molecule. This results in the oxygen atom being slightly negative in charge and the hydrogen atoms being slightly positive. Hydrogen Bonding - The polarity of water allows for hydrogen bonds to occur. The slightly positive charge of the hydrogen atoms in a water molecule will be attracted to and bond with the slightly negative charges of the oxygen atoms in other water molecules. The large number of hydrogen bonds in a sample of water is what gives water many of its properties, such as expanding when frozen and being a very good solvent.
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Cohesion - This is an attraction between molecule of the same substance. Water is very cohesive. Water molecules will draw together, which is why water will bead up when on a smooth surface. Cohesion of water is also what causes "surface tension" which is what allows water gliders and raft spiders to "walk" on water.
Adhesion - This is the attraction between molecules of different substances. Adhesion accounts for the capillary action of water being taken up by plant roots and how the water surface in a graduated cylinder has a curve to it. |
Solutions and Suspensions
Water's polarity allows it to be a great solvent. Water's polarity gives it the ability to dissolve both ionic compounds and other polar molecules. A solvent is any substance in which another substance is dissolved into to create a mixture. A mixture is a material composed of two or more elements or compounds that are physically mixed together but not chemically combined. There are two types of mixtures, solutions and suspensions.
Solutions - A solution is a type of mixture where all the components of the mixture distribute evenly throughout the solution. There are two ingredients to a solution, the solute, and the solvent. The solute is the solid substance that gets dissolved. The solvent is the liquid substance that does the dissolving. In a salt water solution, salt is the solute, and water is the solvent. Solutions are also called homogeneous mixtures. Examples of homogeneous mixtures are coffee, the air we breath, and gunpowder.
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Suspensions - When a material can not be dissolved by the liquid it is placed in, the mixture becomes a suspension. Agitating or moving the liquid will keep the small particles of the solid material suspended in the liquid. When the liquid stops moving, the solid particles will gradually settle to the bottom of the container. Suspensions are also called heterogeneous mixtures. Examples of heterogeneous mixtures are a bowl of skittles, an atom, and sand.
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