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HYDROLOGY Hydrosphere ~71% of Earth’s surface is covered in water What sets Earth apart from other planets Not always here 4.5 BYA Volcanic Eruptions – Lava – hot – Gas – water vapor – Ash – blocks sun • Cools temperature Water vapor condenses Rain falls Oceans form Water Conservation Most of the water on Earth is not suitable for human use 97% is saltwater 80% of all freshwater is frozen in polar ice caps the majority of remaining freshwater is polluted or otherwise unsuitable for use 1/3 of Earth’s population does not have access to suitable water – Landforms – Vegetation – Distance to a body of water – Drought – Contamination – Pollution The one drop from our experiment is not available to people all the time. Properties of Water Most important compound on Earth Tasteless Odorless 2 Hydrogen atoms to 1 Oxygen atom Polarity Universal Solvent Cohesion Adhesion Specific Heat Density Polarity The hydrogen and oxygen atoms are connected by polar covalent bonds – unequal sharing of electrons Since the oxygen is bigger than hydrogen, the electrons tend to stay closer to the oxygen – Oxygen has a slightly negative charge – Hydrogen end has a slightly positive charge Water Molecule Polarity creates poles in water molecules like a magnet. Water has a variety of unusual properties because of attraction between these polar molecules. – The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond. – Each water molecule can form hydrogen bonds with up to 4 neighbors. Hydrogen Bonds Hold water molecules Extraordinary Properties that together are a result of hydrogen Each water molecule can form bonds: a maximum of 4 hydrogen – Cohesive behavior bonds – Resists changes in temperature – High heat of vaporization The hydrogen bonds joining – Expands when it freezes water molecules are weak, – Versatile solvent about 1/20th as strong as covalent bonds. They form, break, and reform with great frequency Polar = uneven distribution of electrons – Has a charge Nonpolar = even distribution of electrons – No charge Like dissolves like – Polar dissolves polar – Nonpolar dissolves nonpolar Universal Solvent Water is an universal solvent – Most substances will dissolve in water Ex. Salt dissolves in water Solvent: substance in which other substances dissolve – water Solute: substance that dissolves – salt Why does salt dissolve in water? Positively charged sodium ions attract the negative oxygen side of water. Negatively charged chloride ions attract the positive hydrogen side of water Water as a Solvent Substances dissolved in fresh and salt water that are important – Dissolved gases: oxygen and carbon dioxide – Dissolved salts and minerals/nutrients (not nitrates) Adhesion Adhesion: molecules that are not alike are attracted – Ex. Water to walls of a test tube or plant walls – Think sticky – Water to the side of a graduated cylinder • Meniscus Cohesion Cohesion: molecules of the same kind stick to one another. – Ex. The reason drops form Organisms Depend on Cohesion Cohesion is responsible for the transport of the water column in plants Cohesion among water molecules plays a key roll in the transport of water against gravity on plants – Capillary Action Adhesion also contributes to capillary action as water adheres to the wall of the vessel. Ex. Water in a straw Surface Tension A measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion – Water has a greater surface tension than most other liquids because hydrogen bonds among surface water molecules resist stretching or breaking the surface. – Water behaves as if covered by an invisible film. – Some animals can stand, walk, or run on water without breaking the surface. – Is why we can “skip” rocks on water Water Strider Can walk on water without breaking the surface tension of water. Specific Heat Specific Heat is the measure of the heat that must be absorbed or lost for one gram of a o substance to change its temperature by 1 C. – A lot of heat energy required to break hydrogen bonds, water resists temperature change • Most heat goes to breaking the bonds..not much left to raise temperature Water = high specific heat – This is why it doesn’t usually snow in Wilmington: – The ocean doesn’t change temperature very rapidly Has a moderating effect on our weather Density Density: how packed together a material is – Mass/volume – Units: g/mL More dense it sinks Less dense it floats Problem: If 60 mL of a liquid has a mass of 30g. What is the density of the liquid? D=30g/60mL D=0.5 g/mL Density of Water Water is one of the only substances that is less dense as a solid than as a liquid. Prevents water from freezing from the bottom up. Buoyancy The force of buoyancy is equal to the weight of the fluid displaced An object with greater volume will be pushed up with more force.
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