Determination of Molar Volume
In this experiment you will investigate the chemical significance of Avogadro’s
hypothesis. You will determine the volume of hydrogen gas evolved in the reaction
between magnesium and hydrochloric acid. From these results determine the mass of H2
produced.
Procedure
Fill a 250 ml beaker half-full of tap water and let stand. Record the temperature and
barometric pressure of the room. Then cut about 5 cm of magnesium ribbon and record
the length precisely. From the mass per meter calculate the mass of magnesium used.
Next fold the magnesium so that it is a small ball and attach it to a piece of copper wire or
string.
Fill the largest beaker in your station ¾ full of water.
Take the gas collection tube and add 10 ml of 3 M HCl to it carefully. Then add tap
water from your 250 ml beaker until the gas collection tube is full. Make sure to add the
water at an angle to keep the HCl from mixing. Place the magnesium into the tube and
fix a single-hole stopper to the end. The stopper should hold the wire/string to the side of
the gas collection tube and not have any air in the hole. Place your finger over the hole
and flip the gas collection tube upright. Stick the tube into the large beaker of water and
clamp in place with a ring stand and utility clamp. The reaction should take place once
the HCl has diffused down the gas tube.
After the reaction get the level of the water in the tube equal to the level of the water in
the beaker and record the volume of gas. If necessary use the 5 gallon bucket. Do this by
placing your finger over the hole of the stopper and then moving to the bucket.
Empty the tube into a sink, rinse the tube out, and put all equipment away.
Data Table
Length magnesium, mass of 1 m of magnesium, mass of magnesium used, room
temperature, barometric pressure, volume of gas collected, pressure of H2 gas, theoretical
volume of H2 gas
Calculations
1)
2)
3)
4)
5)
6)
mass magnesium
moles magnesium
pressure of H2 gas
volume of H2 gas that should have been collected (theoretical volume)
percent error by comparing your actual volume to your calculated volume
volume of H2 gas for 1 mole of magnesium
Error Analysis