Molar Volume Lab Practical                    Name­­_________________________

(Chapter Eleven Test)

                                                                        Period_____

 

 

OBJECTIVE

 

INFO

 

MATERIALS

 

DATA

  1. Vtip              =        mL
  2. length of Mg ribbon   =        cm
  3. Mg conversion factor =        g/cm
  4. level of vinegar         =        mL
  5. Twater             =        oC
  6. Twater             =        K (computer)
  7. Pwater             =        kPa (computer)
  8. Patmosphere       =        kPa (teacher)

 

PROCEDURE

1.    Inspect, clean and assemble the burette.

2.    Fill a 1L-beaker about half full with room-temperature tap water.

3.    Clamp the end of the burette securely with a pinch-clamp, and pour into the burette about 20-30 mL of tap water.  Make certain that no water is leaking out of the nozzle.

4.    Use the pinch-clamp and slowly release water from the burette until the meniscus is exactly at the 50.00 mL mark.  Redo if you over-shoot the mark.

5.    Pour the rest of the water from the top of the burette into a graduated cylinder and measure the volume for the tip of the burette to the nearest 0.01 mL.

6.    Cut a piece of magnesium (mg) ribbon 5.00 cm long.

7.    Roll the Mg ribbon into a loop small enough to fit into the burette, tie an approximately 15-cm piece of cotton thread through the loop of Mg ribbon.

8.    Fill the burette with vinegar (acetic acid, CH3COOH), release a few mL from the nozzle to remove any bubbles in the nozzle, and then fill the burette to the very top.

 

*** RETURN TO DESK ***

 

1.    Insert the Mg ribbon about 2 cm into the tube.  With the thread against the rim of the burette, insert a 1-hole rubber stopper.  The stopper should force water and all air bubbles out of the tube and should hold the thread so as to suspend the Mg in the water.

2.    Place your finger over the hole in the stopper (make sure there is no air in the hole of the stopper), and invert the stoppered end of the tube into the beaker of water. The reaction will not start immediately.  Hold the burette upright.

3.    When the Mg has reacted, and is completely gone, and production of hydrogen gas has stopped, tap the tube with your fingers to dislodge any bubbles you see attached to the side of the tube.  (The suds will have disappeared.)

4.    Move the tube up or down until the water level in the tube is equal to the water level in the beaker.  At this point the gas pressure in the tube will be equal to atmospheric pressure (Patmospheric).  Read the scale on the tube to the nearest 0.01 mL to get the reading of the vinegar level.

5.    Record the water temperature (Celsius).

6.    Use the program Òwater_vapor_pressure_goff_gratch.plÓ to find the water vapor pressure for the water in your beaker.

7.    Record the atmospheric pressure (kPa).

8.    Wash and dry the burette, beaker, etc.

9.    Enter your name and data into the computer. Use the 'molar_volume.pl' program.

 

CALCULATIONS

Show all work.

Show formulas for 4,7, and 10.

            1. mass of Mg in grams

            2. Vbubble in mL

                     (Vbubble = 50.0 – vinegar level)

            3. Vtotal in mL

                     (Vtotal = Vtip + Vbubble)

           *4. PH2 of dry H2 in kPa

            5. VSTP of dry H2 in mL

            6. moles of H2

                     use molar volume and volume from #5

           *7. moles of H2

                     use ideal gas law,

                     PH2 from #4, Vtotal from #3, and Twater from f

            8. actual H2 mass in grams (WYG)

                     use molar mass for H2 and moles from #6

            9. predicted H2 mass (WYSHG)

                     use stoichiometry and mass from #1

          *10. % discrepancy for H2 mass