CP CHEMISTRY II
GASES
NAME
DATE
1
The Big Bang: Hydrogen Preparation and Properties
Introduction
Hydrogen is unique among the elements since it does not seem to belong to a particular family on
the periodic table. In fact, hydrogen is separated from the main body of elements on many periodic tables.
Although hydrogen is classified as a nonmetal, it can react with almost all of the elements. Hydrogen
can combine with nonmetals and have an oxidation number of +1. It can also combine with metals and have
an oxidation state of – 1. Hydrogen is, thus, very versatile in its chemical reactions.
In this experiment, you shall prepare hydrogen gas through the reaction of an active metal with an
acid. The gas will be collected via water displacement. The collected gas will be tested to reveal several
properties of hydrogen.
Materials
ring stand
utility clamp
250–mL Erlenmeyer flask
thistle tube or funnel
2–hole rubber stopper
glass bend
magnesium
18 M sulfuric acid
rubber tubing
4 – 6 gas collection bottles
pneumatic trough
1 – 3 glass squares
10–mL graduated cylinder
wooden splints
lighter or matches
gloves
Safety
Hydrogen gas mixed with air can be very explosive. There should be no open flames in the laboratory when
hydrogen is being prepared.
Handle sulfuric acid with extreme care. Wear gloves when dispensing sulfuric acid. Avoid spills on your
skin or clothing. Immediately rinse any spills with water and NaHCO 3 .
Wear your safety goggles during the entire experiment.
2
Procedures
A.
Preparation of Hydrogen
1.
Place several pieces of magnesium in a 250–mL Erlenmeyer flask. Add enough tap water to just
cover the magnesium.
2.
Securely clamp the flask to a ring stand.
3.
Place the stopper with the glass bend and funnel in the flask. The bottom opening of the funnel
should be below the surface of the water.
4.
Connect the glass bend to the pneumatic trough using the rubber tubing.
5.
Fill the pneumatic trough with tap water. Arrange the trough so that the overflow spout is over the
sink.
6.
Prepare 2 gas collection bottles by filling them with water and inverting them in the trough. Avoid
trapping large bubbles of air in the jars by filling the jar with water until a dome forms and then
sliding a glass plate across the mouth of the jar.
7.
Summon your instructor to check your apparatus.
8.
Obtain 3 – 5 mL 18 M sulfuric acid. Slowly and carefully pour the acid through the funnel and into
the flask. Handle sulfuric acid with respect as it will cause painful burns upon contact with skin. It will also eat holes
in clothing.
9.
Allow bubbles to escape for about 30 seconds. Move one of the inverted collection bottles over the
delivery spot and collect the hydrogen.
10.
When a bottle is full of gas, lift the bottle slightly and slide a glass plate under it. Remove the bottle
from the trough and place it mouth down on the lab table.
11.
Collect 4 bottles of hydrogen.
12.
When you have filled all 4 bottles, pour tap water into the flask to slow the reaction. Remove the
stopper and place it in the trough to rinse it. Then empty the trough and set it aside. The contents
of the flask should be taken to the back sink and poured into the filtering system and rinsed with
water. All rinsed gas collection apparatus should be put in the trough.
3
B.
Testing of Hydrogen and Observations
1.
Burning Splint and Inverted Bottle Test
Light a splint. Keeping the bottle of hydrogen mouth down and vertical, lift one of the bottles of
hydrogen a few inches from the table top and insert a burning splint just inside the mouth of the
bottle. Slowly remove splint. Repeat several times.
2.
Two are Better than One Test
Keeping the glass square in place over the mouth of the bottle, turn a bottle of hydrogen upright on
the lab table. Invert an “empty” glass bottle and place on top of the glass square so that the bottles
are mouth-to –mouth. Slide the glass square away, leaving the two bottle mouths resting against
each other. Wait approximately 30 seconds. Light a splint. With a firm grasp, lift the top bottle
straight up and place the splint in between the 2 bottles.
3.
Set Me Free! Test
Keeping the glass square in place over the mouth of the bottle, turn a bottle of hydrogen upright on
the lab table. Remove the glass plate and wait 5 seconds before bringing a lit splint over the mouth
of the jar.
Questions and Conclusions
1.
Why is it important to have the end of the funnel end below the surface of the liquid in the flask?
2.
Why is the generator allowed to operate for 30 seconds before starting to collect the hydrogen gas?
3.
Write the balanced equation for the reaction used for the preparation of hydrogen (hydrogen should be
a product) in this experiment. Include phase symbols (states of matter).
4.
What product was formed in all of the hydrogen tests?
5.
Write a balanced equation for the reaction that occurred during the hydrogen tests. Include phase
symbols.
6.
Based on observations from this experiment, describe hydrogen’s solubility in water and hydrogen’s
relative density compared to water.