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Draw a water molecule. Label the elements and the charges.
What is the chemical formula for water? H2OH2O Two hydrogen atoms and one oxygen atom
Why is water considered a polar molecule? Because parts of the molecule have either a positive (+) or negative (-) charge The oxygen and hydrogen are bonded because they share electrons, but they do not share them equally. So, the oxygen becomes slightly negative and the hydrogen is slightly positive.
What is a hydrogen bond? An attraction between the hydrogen of one water molecule and the oxygen of a separate water molecule. Hydrogen bonds are like a magnetic attraction- they do not involve shared electrons
Which has stronger hydrogen bonds- water or alcohol? How do you know? Water has stronger hydrogen bonds More drops of water fit on a penny, because they are better able to “hold on” to each other Water needs to be at a higher temperature to boil because the hydrogen bonds are preventing the water molecules from increased movement
What is cohesion? Cohesion is the attraction between two molecules that are the same (water to water) Water is very cohesive because it has strong hydrogen bonds
What is heat capacity? The ability to absorb heat energy without drastic changes in temperature.
What has a higher heat capacity- water or alcohol? Water has a higher heat capacity. Alcohol boiled at a much lower temperature, meaning it’s hydrogen bonds weren’t as strong
What is a solvent? Solute? Solution? Solution: mixture of water and dissolved substances Solute: the material that is being dissolved Solvent: the liquid that the solute is being dissolved into Solution: Salt water Solvent: Water Solute: Salt
What affect do dissolved solutes have on freezing temperature? Dissolved solutes lower the freezing temperature of liquids This is why salt water must be cooled to a much lower temperature in order to freeze that plain water
What is unique about water when it freezes? It expands, causing ice to float Water is the only liquid that does this
Why is the layer of ice on top of lakes important? It provides insulation for the water below
What is the pH of pure water? 77
What is the pH of an acid? In other words, less than 7
What is the pH of a base? In other words, greater than 7
Name three acidic foods Lemon juice, coffee, sour candy Acidic foods taste tart or sour
Name three items that are bases Bleach, ammonia, cleaner
How do you find the average of a set of numbers? Add everything up, and divide the sum by the number of numbers Average of 6, 10, and 5 = 21 21 / 3 = 7
What is the freezing point of pure water? 0 °C
What is the boiling point of pure water? 100 °C
What is a covalent bond? A covalent bond connects two atoms by sharing an electron The hydrogen is bonded to the oxygen (in the same molecule) through a covalent bond
Why is polarity important to life on earth? Since water is polar, water can dissolve lots of substances This is why water is called the universal solvent.
Why is cohesion important to life on earth? Cohesion is responsible for surface tension, which allows certain organisms to float.
Why is adhesion important to life on earth? Adhesion helps move water upwards through the stems of plants, since they don’t have any other way of moving the water against the force of gravity.
How is water’s heat capacity important to life on earth? The water in our cells can absorb a lot of heat energy without killing our cells Oceans can absorb a lot of heat energy from the sun without getting so hot that it kills all of the fish and other organisms.
Water Notes Do Nows, PQQ’s and TOD’s 2.2 Worksheet Complete a cheat sheet Continue to redo the practice test! Practice makes perfect