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PURPOSE:

To predict and measure the effects of the amount of oxygen on the combustion of hydrogen gas, and show that real reactions really do work best when balanced.

BACKGROUND:

Hydrogen gas is highly flammable, and combusts with oxygen to make water.

O2 + 2 H2 2 H2O

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PREDICTIONS: O2 + 2 H2 2 H2O

The chemical equation tells us that for every 1 molecules of oxygen gas and 2 molecules of hydrogen gas, we’ll make 2 molecules of water.

In pictures:

Energy is released ONLY when water is made. The more water made, the more energy released — and the bigger the explosion.

Pop RocketsBut what happens if we have a different number of molecules?

QUESTION: What can we make with 4 O2 and 2 H2 ?

?

Pop RocketsANSWER: We get two water molecules — but three of the oxygen molecules are leftover. So, some of the available energy was not released!

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Beginning Amounts

Ending Amounts

O2 H2 H2O O2 H2

0 6 ? ? ?

1 5 ? ? ?

2 4 ? ? ?

3 3 ? ? ?

4 2 2 3 0

5 1 ? ? ?

6 0 ? ? ?

Now, as lab groups, try to figure out all the other possible combinations of six total molecules. You may split molecules in half if you need to …

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Beginning Amounts

Ending Amounts

O2 H2 H2O O2 H2

0 6

1 5

2 4

3 3

4 2

5 1

6 0

Now, as lab groups, try to figure out all the other possible combinations of six total molecules. You may split molecules in half if you need to …

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Beginning Amounts

Ending Amounts

O2 H2 H2O O2 H2

0 6 0 0 6

1 5 2 0 3

2 4 4 0 0

3 3 3 1.5 0

4 2 2 3 0

5 1 1 4.5 0

6 0 0 6 0

Now, as lab groups, try to figure out all possible combinations of six total molecules. You may split molecules in half if you need to …

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METHOD:

Teams will fill pipette bulbs with different fractions of hydrogen and oxygen gas produced by a fuel cell. You will then launch the bulbs using a piezoelectric igniter, measure the distance traveled, and judge the loudness of the pop.

All teams will start with a half-and-half mix (3 parts O2 & 3 parts H2), and then do two other combinations as assigned.

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STEP 1: Water

Go to the water filling station and fill your pipette bulb with water using the syringe and fill tube.

STEP 2: Oxygen

Go to the “gas station” and fill your pipette with your assigned amount of oxygen (in sixths of a bulb).

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STEP 3: Hydrogen

Fill the pipette bulb the rest of the way with hydrogen, and “cap” the bulb with your finger.

Pipette BulbFill

Tube

Insert the fill tube into the bulb and allow the gas to displace the water — about 1 drop per second.

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STEP 4: Launch

When teams are ready, the bulbs will be launched using a piezoelectric igniter. All teams will judge the relative loudness on a scale of 0 – 10, with the loudness of the half & half bulb (which must be launched first) being defined as “5”. Your team will also measure the distance of flight for your bulb (by counting tiles). Teams will enter their results in the table that follows.

Pop RocketsRESULTS:

O2 H2 Pop (0-10) Distance (tiles)0 6

1 5

2 4

3 3 5

4 2

5 1

6 0

Pop RocketsRESULTS: Averages from 2012 – 2014

O2 H2 Pop (0-10) Distance (tiles)0 6 0.0

1 5 14.5

2 4 19.3

3 3 5 19.9

4 2 17.9

5 1 8.6

6 0 0

Pop RocketsRESULTS: Averages from 2012 – 2014

O2 H2 Pop (0-10) Distance (tiles)

0 6 0 0.0

1 5 6.2 14.5

2 4 6.3 19.3

3 3 5.0 19.9

4 2 3.1 17.9

5 1 0 8.6

6 0 0 0

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QUESTIONS: See handout …