Determination of the Determination of the Molar Volume of Hydrogen GasMolar Volume of Hydrogen Gas

PurposePurpose

To determine the volume of one mole of hydrogen gas at standard conditions.

ConceptConcept

Molar Volume is the volume occupied by one mole of a gas at standard conditions.

(Theoretically 22.4 liters per mole.)

– The student should describe an application of this concept.

SafetySafety

Name H F R Special

Mg Ribbon 2 3 2 Flammable metal

6M HCl 3 0 3 Extreme Corrosive

ProcedureProcedure

Use iron wool to polish approximately 5 cm of magnesium ribbon. Then accurately mass the sample of magnesium.

Procedure.2Procedure.2

With a 20 cm piece of thread, tie one end around the middle of the Mg ribbon and bend the Mg ribbon into a zig-zag pattern.

Procedure.3Procedure.3

Prepare a 600ml beaker two thirds full with tap water. The eudiometer tube assembly will be placed in this beaker later in the experiment.

Procedure.4Procedure.4Prepare the eudiometer tube by placing 15

ml of 6M Hydrochloric acid (HCl) in the tube, then fill the tube to the top with distilled water, being careful to minimize the mixing of the acid.

Procedure.5Procedure.5Quickly place the Mg

ribbon in the top of the eudiometer tube and pinch the thread between the stopper and the wall of the eudiometer tube.

Procedure.6Procedure.6

With out letting in any air bubbles, invert the eudiometer tube assembly into the water bath; allowing the contents the ability to flow into the water bath.

Procedure.7Procedure.7

Make and record observations.

Notice the density currents caused by the ‘sinking’ HCl.

It makes the solution look oily.

Once the acid reaches the Mg it begins to produce H2 gas.

Procedure.8Procedure.8

Record the volumeof the gas produced.

44.61 ml

(read at apex of meniscus)

Procedure.9Procedure.9

Record the height of the water column, in millimeters, above the level of the water bath.

11.65cm high or 116.5 mm of water

Procedure.10Procedure.10

Record the temperature and the atmospheric pressure.

Calculations.1Calculations.1

The pressure of the dry H2 gas must be calculated.

There are two corrections to be made. – The water vapor mixed in with the collected H2

must be corrected. – The pressure difference between the inside of

the tube and outside the tube must be accounted for.

Calculations.2Calculations.2

The pressure in the tube is less than the pressure outside the tube

The difference in pressure can be calculated by dividing the difference in water levels expressed in mm of H2O by 13.6 because mercury is 13.6 times more dense than water.116.6 mmH2O 1.00 mm Hg

13.6 mmH2O= 8.57 mmHg

Calculation.3Calculation.3

The total pressure inside the tube is the atmospheric pressure minus the water column pressure difference.

774.2 mmHg – 8.57 mmHg = 765.6 mmHg

Calculations.4Calculations.4

Because there is H2 and H2O in the tube, the pressure of the water vapor must be subtracted.

Look up the water vapor pressure for the temperature of the gas.

The vapor pressure of water at 22.7°C is 20.7 mmHg

765.6 mmHg - 20.7 mmHg = 744.9 mmHg

ConclusionConclusion

A good conclusion includes– a summary– results– sources of error– describes an error propagation.