Chemitry Lab - Molar Volume of a Gas

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The molar volume of hydrogen gas        20.10.2009

Introduction:

In this lab I am going to find out the volume of one mole of hydrogen gas at room temperature and atmospheric pressure. The room pressure only slightly differs from the standard, but can be taken into consideration when calculating the results. The molar volume is 22.41 liters per mole at STP (Standard pressure), in other words, at zero degrees centigrade.

Figure 3.1 (the experiment set up)

Procedure:

  1. Set up all equipment.
  2. Cut a piece of Magnesium ribbon about 20cm in length.
  3. Calculate the weight of the ribbon from the weight of a 1 m long ribbon.
  4. Measure 1.0 M Hydrochloric acid to a volume of 25-30ml.
  5. Pour the HCl to the reaction flask.
  6. Add the Mg ribbon to the reaction flask and secure the mouth of the flask as fast as possible with a hose. Make sure that the hydrogen gas cannot escape from the flask.
  7. Follow the temperature
  8. Collect the gas until no further reaction is observed in the reaction flask.
  9. Carefully remove the gas collection flask so that no gas escapes from the flask.
  10. Light the gas.
  11. Determine the volume of the gas.
  12. Calculate the molar volume of H2 gas at room temperature.

a) theoretical value from Vm =22.44 l/mol at STP.

b) experimental value from your data.

Equipment:

  • 2 flasks (volume at least 600ml)
  • large container (volume at least 3,5 l)
  • Magnesium ribbon
  • 30ml of Hydrochloric acid
  • thermometer
  • a hose (to cover the reaction flask)

Observations:

  • Magnesium ribbon was a little oxidized for it had lost some of its shine.
  • When the collection flask was turned around and placed in the water filled container, there were tiny air bubbles on the inside walls of the flask.
  • When Magnesium ribbon was added, it began to corrose in the HCl
  • Instantly after adding the Mg ribbon to the hydrochloric acid, temperature in the reaction flask  started to rise as a chemical reaction took place in the flask.
  • Moisture and (fog) blocked the view of the reaction
  • Immediately after adding the Mg ribbon, hydrogen bubbled  to the collection flask
  • Hydrogen bubbled to the flask for about a minute,stopping soon after the ribbon had corrosed in to the HCl.
  • There was a hissing sound as the chemical reaction occurred in the reaction flask and the gas flowed to collection flask through a pipe.
  • The temperature in flask A rose quickly by a few degrees celsius and then stayed nearly constant for the 15 minutes the temperature was measured.
  • The temperature did not change in flask B;however, it cannot be stated for sure as it was only compared with the temperature of flask A.
  • The temperature in flask A rose very quickly as the reaction started
  • The amount of hydrogen produced from the reaction was large for large bubbles of gas rose to beaker B  within few seconds after starting the experiment
  • The volume of the reaction flask was not measured, but it is close to the volume of the other flask (629ml)
  • After the reaction, when lighting the hydrogen gas, collection beaker made a popping sound but the  reaction flask actually burned and formed a thin flame.
  • The flame from the reaction flask gave out a lot of heat, which was not noticed when lighting the gas in the collection flask.
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Figure 3.2

   

      Figure 3.3

       

     

Calculations:

1.000m ± 1mm of Mg ribbon weights 1.06 g ±0.005g

25.8cm ±1mm Mg ribbon used   weight = 0.27348g

1.06g   × 25.8cm  = 0.27348 ± 0.96% (0.003g)

 100

30ml ± 1ml (3.3%) of HCl

m(Mg)=0.273g

M(Mg)=24.31

n=0.273 = 0.011                            n(H2)

     24.31

Molar volume at the conditions in the room?

molar ...

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