Chemistry

The Phases of H20

By:Yianni Skourtis

    Purpose: To create a heating curve displaying the
temperature of water that is heated over time and to analyze
the properties of H20 while being heated.
    Introduction: This lab explores the qualities of water during its heating, or adding kinetic energy to it. Heat is energy in transit that moves because of a difference in temperature between objects. Heat always flows from a hotter object to a cooler one. When heat is added to an object, its average kinetic energy increases, and so does its temperature. Temperature is a quantity telling how much heat an object has. There are three major temperature scales; they are Fahrenheit, Kelvin, and Celsius, which will be used in this lab. On the Celsius scale, 0° is the temperature at which water freezes and 100° is the temperature at which water boils.
    The unit for heat is the calorie. A calorie is equal to the amount of heat needed to raise the temperature of one gram of water by 1°C. A kilocalorie is the same as a Calorie (note the capital C), they are both equal to one thousand calories. A Calorie is the unit used to measure the amount of heat food gives off. The amount of heat needed to heat an object depends on three things: one, the mass of the object, two, the difference in temperature, and finally, the specific heat of the object. Specific heat is the amount of heat re- quired to raise the temperature of a unit of mass of a sub- stance by one degree Celsius, usually measured in calories! gOC. Water's specific heat is 1cal/gOC, which is fairly high compared to that of other substances. Because water has a high specific heat it resists change in temperature.
    Heat and energy can be transferred in three ways: radiation, convection, and conduction. Radiation is the transfer of heat energy by electromagnetic waves, which is how solar energy gets to Earth. Convection is the transfer of heat through the currents of fluids. For example, if one part of a body of water is hot and the other is cold and the water is stirred, the water will reach thermal equilibrium through convection. Conduction is the transfer of heat between two objects that are in contact with one another. This happens be- cause the molecules of the hotter object vibrate and move and hit the molecules of the cooler object, giving that object more energy and heat. Conduction is the type of heat trans- fer that occurs in this lab between the heating plate and the beaker of water.
    A heating curve is a graph that plots the temperature of an object vs. the time it was heated for. It should appear as a flat line, then a slope up, then another flat line. This lab created a heating curve for water using the data points we collected during our experiment. While the water melts and boils, the line on the curve should be straight. This is because the water uses all the energy from the heating surface to change phase, not increase temperature. Melting is the change of phase fonn solid to liquid, and boiling is the change of phase from liquid to gas that occurs when vapor pressure is at equilibrium with atmospheric pressure.
    To change Ig of H2O to liquid phase, you must add 80 calories of heat. During this time, a heating curve would show a flat line because there is no increase in temperature. Another flat line appears during the heat of vaporization; this is when liquid H 0 is heated to fonn gas, or water vapor. It's flat at this pbint for the same reason as heat of fusion; the temperature doesn't go up, a change of phase occurs, instead.
   An object can only go from solid to liquid or liquid to gas if it gains energy. When the molecules of an object gain kinetic energy, they move faster, and if they move fast enough they can break away from the other molecules. When a molecule breaks away from the structure it was in, it has changed phase. When the temperature of the water increases it shows up as a slope on a heating curve, as opposed to the flat line when it changes phase. An ideal heating curve for this temperature range looks something like this:

Materials and Methods:
1) Collect the following materials.
-A heating plate (be sure an electrical outlet is near)
-A glass beaker, able to hold about a liter of liquid
-Enough ice to fill the beaker halfway -Thermometer (Celsius) -Stirring rod -Stopwatch
-Safety Glasses for each member of your lab team
-Graph paper or computer graph program
2) Make sure each member of your lab team has a job and is wearing safety glasses. One person should be the temperature recorder, one person should tell the recorder when to record the temperature, one person should write down the data, and one person should carry out various other assignments.
3) Create a table to make it simple to collect data during the experiment.
4) Turn on the heating plate to 500 watts.
5) When the heating plate is fully heated, fill the beaker halfway with ice and immediately place it on the heating plate and make the first temperature reading. You can use the stirring rod to be sure the water and ice are at thermal equilibrium. Be sure not to touch the thermometer to the bottom of the beaker because this will record an incorrect temperature.
6) Every two minutes record the temperature of the water in the beaker and record it on your table.
7) When the temperature of the water has been recorded at or above 100°C a few times remove the beaker from the heating plate and stop tak- ing data.
8) Unplug the heating plate and dump the water and put away all materials.
9) Using the collected data create a curve chart displaying temperature (on the y axis) vs. time (on the x axis).
10) Analyze this data and see what you can conclude about water's temperature while it changes phase and as energy added.
    Results: Many observations were made during this lab. First, when the ice was initially
placed in the beaker and it's temperature was taken, it was not O°C, but a little more than 1°C, as seen on the table. After the ice had fully melted and only water was in the beaker, at about 12°C, the temperature was going up at about even intervals. These intervals were about 8°C every two minutes, this varied though. Sometimes it only went up by 6°C, and sometimes it was 9°C. At about 91°C the water was slowly boiling, this occurred within 36 minutes of the lab starting. By the 100°C mark, the water was fully boiling and the next few measure- ments did not raise in temperature much, which meant the lab was done. The [mal temperature was 101.3°C; this was 44 minutes after the lab began. When the heating plate was shut off the boiling stopped quickly.
   
    The Table below shows the temperature vs. time data. The experimental errors are listed in parenthesis.
Temperature (°C) (.1)        Time (sec.) (1 )
          1.4                                12  
          1.9                                124
          1.9                                248
          2.0                                361
          3.9                                490
          5.6                                600
          9.2                                736
        12.5                                862       
        17.8                                972
        22.5                                1084
        31.2                                1202
        37.9                                1329
        45.3                                1443
        53.9                                1562
        62.1                                1685
        69.9                                1810
        78.7                                1941
        85.1                                2065



    Discussion of Results and Conclusions: Many conclusions can be drawn from the data collected in this lab. The H20 and its temperature did interesting things while being heated. First, when the ice was placed on the heating plate, its temperature didn't rise significantly for almost 7 minutes. This happened because all the energy from the heating plate was going into changing the waters phase. The molecules of the H20 gained enough energy by the 8th minute to break the attractive force of the other molecules and become a liquid. When all the molecules of H20 were in liquid form, which meant only water was left in the beaker, the temperature of the water began to rise quickly. This occurred because all the energy from the hot plate was going straight into increasing the internal energy of the molecules and average internal energy is directly proportional to temperature. Until the water reached temperatures in the high nineties it increased by even increments. At that point, the water began boiling slowly, and then quickly at temperatures above 100°C. As soon as the water was fully boiling, the temperature of the water stopped rising. The water stopped increasing temperature when boiling for the same reason it stopped while melting; all the energy going into the H20 went into changing phase. The molecules of H20 were ganing so much kinetic energy they could completely break away from the liquid molecules and turn into a gas above the beaker, which was steam.
This lab ended with boiling water, which is an interesting phenomenon. The molecules of water have a pressure that pushes against atmospheric pressure, it's called vapor pressure. At room temperature, atmospheric pressure is much greater than the vapor pressure, but not at higher temperatures. When water is heated, its molecules move faster and they have higher average kinetic energy. The faster they move, the more pressure they exert. At 100°C, the boiling point of water, the vapor pressure of water is equal to atmospheric pressure. This is when tiny gas bubbles have enough pressure to keep in bubble form until they reach the surface of the water and escape. That is why when water boils many bubbles come from the bottom to the surface.
This lab's purpose was met. A heating curve was created that reflects the data we collected and resembles the heat curve we were aiming for. The data we collected was also used to find how H20 acts when heated. Although the lab was successful, there was error involved. First, the temperature of the ice water was never 0°C, which it should have been. This could mean a few things, either the there mometer was calibrated incorrectly, or the water and the there mometer hadn't reached thermal equilibrium yet. Also, the atmospheric pressure may be different in the area where we were than is normally calculated, which would change the water's melting and boiling points. Another error involved with the thermometer was how it was read. We read it to the .1°C, even though it was difficult to see that closely. Also, the timing of the temperature checks were never exactly two minutes apart, so the increments are not exactly even, al- though they are close. The times of temperature check are only accurate to the second, also. Another source of error was the temperature of the heating plate, which may have fluctuated and was different for every lab group. Despite these sources of error, the lab was effective in reaching our purpose.
Knowing what I do now, if I were to perform this lab again, I would make many improvements. First, I would set the heating plate at a higher setting so the lab would not take as long. Second, I'd put the ice in and give the ther- mometer enough time to reach thermal equilibrium with it. Doing this would start the lab off at the correct temperature, DOC. I would also leave the thermometer in instead of tak- ing it out after every reading. This would allow us to make the readings at much closer to the two minute increments we had set out to take. I'd also reduce the increments of taking the temperature to one minute because the heating plate is hotter and the more data the better. Finally, I would stir the water more often to make sure it was all the same
temperature.
In conclusion, this lab was effective in helping us analyze H20 while it was being heated. We also found that the tempefature of water over a period of time while being heated does fit a heating curve. This lab did have error and could be improved but it was still successful in its purpose. A heating curve is an accurate representation of H2O's properties when heated from ice to gas or frozen to boiling.

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When it rains...

By: David Zahora

    The main purpose of this lab was to see the effect that acid rain will have on plants by seeing how it affects the soil. This happens when the acid rain leaches the chemicals out of the soil that are necessary for plant survival. This lab showed us how and why the minerals in the soil are lost to the acid rain. It also showed us how different pH levels can affect the amount of leaching. We also learned how and why limestone is useful as a buffer to the acid rain. Now we know why much of the wildlife is being destroyed around and downwind of large industrial areas. More importantly, we know what causes the destruction of the environment and we can find ways to prevent it.
    The data from this lab is the pH readings of the soils with and without acid rain along with the 6 tests that we did in order to determine if the rain had leached out: Magnesiurn,lron, Copper, Chlorine, and Phosphates.

PH

                                                                    Water              Acid Rain                     Lime
Ph of solution                                                   7                         1                             1
                                                                                                                         (just the acid rain)

ph in soil                                                           7                      46/7
                                                                                                                         (after lime addition)

Test for Leached Chemicals

    The purpose of this lab was to find out how acid rain would affect plants and the lab showed us that. One of the major reasons that plants die because of acid rain is because the acid rain leaches out the chemicals that are essential for the survival of the plant. We observed this in our lab by putting the acid rain and distilled water in the soil samples and then filtering it This is a representation of what happens when water goes through the soil in real life. The filtered substance then will contain all of the particles that were taken out of the soil. However, the important thing to know is that the more chemicals found in the filtered solution, the worse. Since these are the chemicals that are taken out, you don't. want any because then they aren't available for the plant. . . Thus the distilled water only takes out a few chemicals while the acid rain takes out more. It is important to understand beforehand that we want less chemicals in the solution because that means that less chemicals were leached out.
    The actual reason that plants die from acid rain is that the plant need the chemicals that the acid rain leaches out to survive. Without the macro and micro nutrients that the acid rain steals, the plant goes through a variety of conditions depending on the individual chemical. Such conditions are the stunting of growth, poor roots, membranal breakdown, and death. In our lab, the soil leached out primarily Ch, Ca, and Ma. If there had been plants in this soil, the lack of chlorine would make the plant have small leaves and have slow growth, the deficiency of Calcium causes meristem death, abnormal cell division, and membranal breakdown, finally the lack of magnesium causes chlorosis: An abnormal condition in plants, characterized by the absence of green pigments in a plant caused by the lack of sunlight or minerals. Basically, the lack of minerals in the plant causes irregularities in plants and can often lead to death. It is important to know what the symptoms are so that specific mineral loss can be treated.
   The scientific reason that the chemicals leached out is due to electro negativity. In the soil the minerals are positively charged and are bonded to negatively charged particles in the soil. The defining quality of an acid is the existence of an H+ ion, another positively charged ion. When the acid rain enters the soil there is a conflict between the positively charged H+ and the positively charged mineral. Electronegativity is the affinity of two elements to join together. The greater the difference between two elements, the more likely they are to bond. In this case the electronegativity of the H+ is such that the particle in the soil want to bond more with the H+ rather than the minerals. Thus the minerals are not bonded to anything and when water runoff comes, the minerals are taken away with the water and the plant can't use them. This is the reason that acid fain is a problem, because as more and more acid rain is generated, more of the H+ ions bind to the soil molecules and the minerals are swept away.
   PH is a measure of the acidity or alkalinity in a substance. That means that it measures the amount of H+ and OH- ions in a substance. A substance with a pH of 1 can be assumed to have more H+ ions that a substance with a pH of 3. This plays into affect With the leaching of chemicals because the stronger the acid, the more H+ ions, and the more bonds can be interrupted in the soil If the soil is exposed to an acid with a pH of 1 like hydrochloric acid or sulfuric acid, then more H+ ions are around to take the place of the minerals. This is important because of the chemicals that are in acid rain. A majority of acid rain is caused from sulfuric acid that forms when the chemicals released from power plants join with rain. This means that the acid will have a very low pH which was proven when we did our pH test on the chemicals and found it to be a pH of 1. This means that the maximum number of H+ ions are present and that means more minerals can be leached out.

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