Properties of Water
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Properties of Water

EXPERIMENTAL SECTION

Today it will seem as though this is more a physics lab than it is of biology. But remember biology is built upon physics. Many people are now beginning to say that biology is the difficult science because you have to know all the other sciences in addition to the biological aspects. Today's lab will be concerned with that most common substance - WATER. Water forms the major portion of most living organisms.(1) Thus a knowledge of the properties of water is not only important - it is literally "vital."


(1) A possible final exam question: name some living organisms in which H2O is less than 50%

(2) STP = standard temperature and pressure = 20°C; 1 atmosphere of pressure.


Let's look at some of H2O's properties.

Reiteriterating (sic!): we are looking at what effects temperature has on these properties. Why temperature? H2O has another unique property: liquid H2O requires more heat than any other non-ionic substance to raise a gram one degree. How can such a "light" (non-massive) substance absorb so much heat with so little effect? Therein might lie an answer to the mysterious characteristics of H2O.

Graphing experience. In addition, today's lab will give you exercises in graphing techniques. Graphs are one of the most powerful devices for describing and predicting science. So you will have some rather simple experiments from which data will be gotten and then graphed in appropriate ways.


GENERAL INSTRUCTIONS

The instructor will give you a double-sided data sheet to be filled in. On one side, at the top, there are five columns (temperature) and three places for you to put the following data. Near the bottom, is place to collect data for the needle experiment. The other side of the page is for collecting and evaluating data for the adhesion experiment, which you will start now, and finish last. Only the needle experiment will not be run simultaneously with the following experiments. So do these first and then set up for the needle experiment.


WATER - A LIQUID!

On the attached data page is a list of gases (at room temperature). Next to each write down your calculation of their molecular weights (note: not "atomic weights"). You need only integers, please. Finally, there is a box for you to write down the molecular weight of water.

How can water be a liquid at room temperature? Its molecular weight is too light! Could it be that your calculation of the molecular weight of water is wrong? About what molecular weight should it be in order to be a liquid? Let's assume that chemists are correct in that there are twice as many H's as there are O's. Using your estimate of what water's molecular weight should be, can you calculate the functional molecular formula be for water to have that "minimum" molecular weight? (Hint: might it be H8O4?)

Why do you think that water's functional molecular weight is so much higher than what the chemistry texts report? (Hint: think and discuss among yourselves "H-bonds.") Under what condition does a water molecule truly have a molecular weight of 18?

We are now getting a glimpse of the wonder of water, that life-giving liquid. Let's press on!

For those of you who have been confused about the Gibbs-Helmholz Equation, which relates enthalpy, entropy and free energy in a single equation, you might find enlightenment in looking at it from the perspective of the properties of water. We dare you to click HERE!




ADHESION EXPERIMENT USING VARIOUS FABRICS

  1. Fabrics are made from various fibers.
    1. Hair (wool) and silk are protein chains of amino acids), and nylon is a manmade compound that mimics protein.
    2. Cotton and linen are carbohydrates (chains of sugars);
    3. Polyester and rayon are manmade also but are not mimicking any natural fiber.
    4. Bits of sponge and animal skin are other candidates for testing adhesion.

  2. From the various fabrics on the side-bench, collect duplicate sets of different fabrics. The type of fabric is indicated by the code letter written on them. Don't worry about colors.

  3. Weigh each swatch separately to the nearest 0.1 gram and record their dry weights.

  4. Read the next seven (5 through11) steps before starting them.

  5. Place one set - one by one - into an ice water bath to saturate them. Place the other set into the hottest water your hands can stand.

  6. (This can be messy, so do this by a sink! AND do it quickly!) Try to make an underwater sandwich of all the swatches, or lift out each piece and lay it flat and sopping wet on a drainboard that empties into a sink, immediately lay another on top of that, and so continue to build a layered sandwich.

  7. Immediately, starting at an edge (not a corner) roll up the sandwich.

  8. Dip the roll into its water bath for a few seconds to re-equilibrate its temperature.

  9. Over a sink, wring it out as hard as you can (how hard will turn out to be a relatively unimportant variable!).

  10. Immediately place the roll in a zip-lock bag, seal and place it in its bath for about 30 minutes. This will allow the water to distribute itself as it will among the fibers. (The class may have to share large baths, so use a Sharpie and label your bag. The hot bath should have a constantly flowing stream of hot water going into it.

  11. At this point the class should jump to doing the viscometer, and surface tension experiments.

  12. After 30 or so minutes, take the bag to a scale and quickly weigh each piece; wiping dry the scale after each weighing. Let your secretary with dry hands do the recording of values.

  13. While other group members begin to "crunch" the numbers for the data sheet, take the damp pieces of cloth to the designated area for drying.


VISCOSITY AND SURFACE TENSION EXPERIMENTS

START Assign your three group members among these three tasks:

  1. Secretary, clock-watcher and reservoir manager: From the water-and-ice bucket, fill your foil container with just liquid cold water. Insert the thermometer, record the temperature. It should be very close to 0°C. Record that temperature's value atop the first column.
  2. Viscometrist: The viscometer is a long flexible plastic tube containing water, and a bead, that can move from one end to the other. (The smaller the bead the slower it will sink. Thus a small plastic bead will sink slowly (good for low viscosity fluids), and a small steel ball bearing from your hardware store will sink fast (good for high viscosity fluids).) Obtain one, and totally submerge the "viscometer" into the icey water in the foil container.
  3. Surface tensionist: Get a drycoin (the bigger the better), and rub it with the piece of oiled cloth. Then place it into a dry petri plate boat and float it in the icey lake in the foil container. / Also insert the 10 ml pipette into the water so that it fills to above the 0 ml mark.


Your group is now ready to start the three sets of measurements. (If each of you takes responsibility for one of these, you will get finished early because they can be done simultaneously!)

  1. Viscometrist: Take hold of one end of the viscometer and lift it out of the reservoir; hold it vertically and allow the bead to settle to the bottom. At time = zero, quickly invert and stretch it straight, then time in seconds how long the bead takes to reach the bottom. Record that number.

  2. The person with the 10 ml pipette and the coin in the boat: Submerge your pipette so that it is filled to over the 0 ml mark. Hold pipette vertically, drain the pipette to the 0 ml mark; place the tip of the pipette about 1 mm over the coin and slowly allow the water to flow onto the coin. The water will initially bead up on the coin. When the water first overflows, record the volume delivered. Yes, you must dry the coin between re-uses!

  3. Now change the temperature in the foil container to somewhere between 20° and 30°. Record that temperature at the top of the next column. Now go back to step A, B and C. Collect data for at least four temperatures (for example: 0, 20, 45, 65 and near boiling). Don't be a "dummy:" you do not have to use those exact temperatures; just record what temperatures you did use.


NEEDLE EXPERIMENT

This is an adaptation of the old parlor trick in which you amaze your friends by floating a solid metal sewing needle on the surface of water. But instead of sewing needles of unconstant diameters, you are provided with steel wires that are precisely gauged.

Examples of Steel ("Music") Wires from ACE Hardware
Diameter (inches)Rel. mass/lengthCut Length (mm)ACE Stock No.
0.0151.0036498
0.0201.7841499
0.0252.7843500
0.0324.5545501
0.0396.7650497
0.0479.8253502
0.05513.4458503

Obtain a set of steel wires from the instructor. They are of different gauges (diameters). The teacher will photocopy a set of wires for your comparison. The thicker the wire, the longer the wire.

Set your foil container on a cool hot plate ("off"), and fill with 0° water. Slip your thermometer into the water at an angle so that you can read it without moving it.

Carefully float your needles on the surface of the water. (A helpful device is a reshaped plastic covered paper clip as shown in an old picture on the right where a threaded needle is used. You will use the gauged wires, of course.) Figure out how to keep the wires from coming together in rafts. (Hint, hold an extra large wire over those that are floating. Because these steel wires are slightly magnetic, you can guide the wires around on the surface!) The wires MUST be separated for this experiment. RECORD the gauges of the wires that could be floated versus this ice-water temperature.

Turn on the hot plate. Record the temperature and the gauge as each wire sinks. Do this experiment two or three times and average the results. (Yes, you must dry the wires before attempting to refloat them!)


MANAGING THE DATA

As temperature increased,

  1. were more or fewer milliters able to fit atop the coin. Show this by making a graph.
  2. did the bead sink faster or slower in the tubing? Show this by making a graph.
  3. were larger or smaller wires able to float longer? Show this by making a graph.
  4. Extra credit: Does the length of the wire make any difference?

Obtain a piece of graph paper from the instructor, and follow the verbal directions as to how to set it up. Graph the collected data. Have your graphs approved by the instructor.

With reagard to the adhesion experiment:

  1. List the fabrics in decending order of adhesion to water.
    Does the order of your list correlate well with the lists from other groups?

  2. Did temperature have any effect(s)? If so, why, based on chemistry, do you think so?


DISCUSSION

WHY? What happened? What properties of water were susceptible to temperature? How can this be?

How is this important to LIFE?


COMPARE YOUR GROUP'S DATA WITH OTHER GROUPS

Did you get the same results? What about the bead's sinking time?-! (Here you will learn about normalizing your data because this will allow you compare your data with those of another group, who may have equipment of a different size.)

Normalizing. Divide the sinking times of all your temperatures by that at 0°. Then multiply all of those answers by 100 to give you PERCENT. (You did it right if your 0° result is 100%!) Now you can add your numbers to a "class graph" - a master graph for the whole class. Do your numbers fit in line with those of other groups?


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