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Freezing and Melting of Water

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Freezing and Melting of Water Introduction The water molecule (H2O) is formed by one atom of oxygen, bound to two atoms of hydrogen. The hydrogen atoms are "attached" to one side of the oxygen atom, resulting in a water molecule having a positive charge on the side where the hydrogen atoms are and a negative charge on the other side, where the oxygen atom is. Since opposite electrical charges attract, water molecules tend to attract each other. All these water molecules attracting each other mean they tend to clump together. Earth's water (about 70 percent of the Earth's surface is water-covered) is constantly interacting, changing, and in movement. The freezing temperature (the temperature that a substance turns from a solid to a liquid) is 0o on the Celsius scale, and 100o is water's boiling point (at sea level; 1 atmosphere pressure, 76mm Hg or 101.3 KPa.). Another important characteristic is that water has a high specific heat index. This means that it can absorb a lot of heat before it begins to get hot. ...read more.


Part II Melting 1. 250-ml of warm tap water was obtained in the beaker. When 12 minutes had passed the test and its contents were immersed into the warm-water bath. 2. Data collection was stopped after 15 minutes. 3. The flat part of the graph was analysed to determine the melting temperature of water. 4. The melting and freezing curves were compared. 5. A graph of temperature vs. time (with two curves displayed) was printed. Data Analysis Questions 1. Explain the shape of the curves in terms of the energy changes that are occurring in the sample as it heats up and melts and as it cools down and freezes. 2. Explain how an increase in the amount of water used would affect the shape of the curves. 3. Explain in your own words what is going on at the molecular level as liquid water cools and freezes. 4. Construct a model that illustrates the energy effects and the structural changes that occur during a change of state. ...read more.


The attractive forces between the molecules prevent most of them from escaping the liquid. However, when the water cools down and freezes, the molecules became strongly attracted to each other. The motions of the particles turned minimum and now they tend to vibrate about fixed points. That's why a solid has a definite shape and volume and the liquid has a fixed volume and takes the shape of its container. Discussion In the first part of the experiment, problems occurred with the TI Graphing Calculator. When finally the calculator was correctly set up, then the experiment went very well. Conclusion In this experiment essential findings were discovered, such as the flat part of the graph when the substance (in this case, the water) is changing state. Analysing the melting and freezing graphs, we found the flat part between 200 and 375 seconds at 0 o (in the freezing graph) and between 200 and 675 seconds at approximately 0 o (in the melting graph). The inclined parts of the graphs are obviously because the increasing or decreasing of kinetic energy of the particles. The experiment was well conducted and the aim, to investigate the cooling and warming behaviour of water, was achieved. The steps were correctly followed. ...read more.

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