Chemistry 11 Lab #4/5

Properties of Water

Theory

The theory for station 4 is a bit tricky and you may want to wait until we have done this more in class:  Heat from the water and the steel calorimeter container is tranferred via conduction to the ice cube.  The heat lost by the water and steel is given by:

qlost=mwatercwater (Tinitial - Tfinal) + msteel csteel (Tinitial - Tfinal)
       = (mwatercwater + msteelcsteel) (Tinitial - Tfinal)


 where, m represents mass, and c represents specific heat capacity.

The heat gained by the ice cube is a bit simpler (if we assume it starts at its melting point) as the heat it gains results first in it melting and then in rising in temperature from zero celsius to Tfinal :

qgained =mwaterLwater + mwater cwater Tfinal
           = mwater (Lwater + cwater Tfinal )

Conservation of energy tells us that qlost = qgained so from the above equations for these we can get an equations that can be solved for the latent heat of fusion for water.  Your job is to carry out these last steps of the calculation.

Procedure

You should work quickly through the parts of the lab involving ice. To do this it will require that you read through the procedure before you begin each section. The lab will be set up with a number of work stations. You should do part 1 as soon as possible (ensure you get it done the first day) but you can do the other stations in any order you choose. It is crucial to get reading errors for each measurement. This lab will take a couple of weeks...

Station #1 Temperature vs Time Graph for Water

Get the data for this one and we will go to the computer lab next class to graph it in Excel.
  1. Fill a 250 mL beaker up to about 100 mL with water and add two or three of cubes of ice crushed up. Ensure that the mixture comes to 0oC and there is still some ice present.
  2. Place the beaker over a bunsen burner and clamp a thermometer in the mixture but off the bottom of the beaker. Make a data table for temeprature and time measurements. Take an intial reading (0oC at 0 seconds). Light the flame and take temperature measurements every 20 to 40 seconds.
  3. Note some special points: when the ice has all melted; when bubbles first begin to form (this is the false boiling point - what are those bubbles?) and when the water begins to boil. Coninute taking measurements until the water has been boiling fully for more than two minutes.
Station #2 Density of Liquid Water and Ice
  1. Choose whichever method you think is most appropriate for getting the density of liquid water. The equipment you used in Lab #2 for getting the density of saltwater will be available. Give a defense for whichever method you choose.
  2. Use the displacement method to find the volume of ice by allowing a mixture of equal amounts of ice and liquid water to sit in a 500 mL beaker together for a few minutes. (This ensures that the ice and water come to thermal equilibrium so the ice will not continue to melt while you perform the rest of the procedure.) Pour the liquid water into the 500 mL cylinder and quickly mass the beaker and ice.  Note the volume of liquid water and then add the ice to it, noting the new volume (ensure the ice is submerged).  Finally, mass the empty beaker. The volume measurements can be used to get the volume of ice via displacement and the masses can be used to calculate the mass if ice. Write the equations out for these calculations.
Station #3 Density of Water Vapor at the Boiling Point
  1. Use the electronic balance to mass the empty beer can and read the volume from the side of the can.
  2. Add a few mLs of water to it, cover the opening loosely with tin foil and place the can over a bunsen burner while holding it with a folded piece of paper.
  3. Carefully listen for evidence that the water has boiled away (it stops making the boiling sound) and then remove the can from the flame.  Allow it to cool a few minutes with the tin foil in place. The boiling water has turned to steam and filled the can with water vapor while expelling air from the can. The foil holds the vapor in. After cooling the vapor recondenses as liquid water.
  4. Remove the foil and mass the can.  (The mass difference before and after will be the mass of water vapor in the can when you removed it from the flame.  The volume of the vapor at that time should be written on the side of the can!)
  5. Use the mass of vapor and volume to get the density of water vapor (at about 92 celsius).
  6. For a thrill you should try boiling a few mLs of water in the can as above and then plunge it quickly UPSIDE DOWN in the basin of water. Observe what happens and explain it.
Station #4 Latent Heat of Fusion for Ice
  1. Mass the inner container of the calorimeter and read its specific heat from its side.
  2. Fill it about halfway with liquid water and weigh it again with the pan balance.  (The difference in mass will be the mass of water.)
  3. Take a small piece of ice (one cube) and allow it to sit out until a bit melted.
  4. Take the temperature of the liquid water.
  5. Dry the ice with a paper towel and mass it quickly, then add it immediately to the water in the calorimeter.
  6. Allow the mixture to sit with the calorimeter cover on for a few minutes, then check to ensure the ice has all melted and take the final temperature.
Known Densities
0.59 kg/m3 for water vapor
917 kg/m3 for water ice
1000 kg/m3 for liquid water
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