A.M. Test Review

Alkali Metal Test Review - Part 1

Using the observations of the alkali metals and science developed in class, generate an explanation of the phenomena.

Alkali Metal Phenomena (New / Better) .mp4

The below observations of the phenomena will require an explanation on the test

Observations

When lithium and sodium are placed in the water, the piece of metal gets smaller and smaller until it can no longer be seen. As this is happening, something can be seen going into the water.
1. The same thing happens with the other alkali metals but the reactions occur so quickly that it cannot easily be observed
Bubbles can be seen in the water where the water and the piece of metal are in contact
1. With lithium and with sodium, a test tube is used to collect the gas in the bubbles. The test tube is placed near a candle and the gas collected from the bubbles catches on fire.
2. With the rest of the metals, the flammable gas catches on fire without the candle

Science that students developed during this unit / past units that now must be applied to the phenomena.

Charged atoms / molecules will dissolve in water (zinc lab / copper lab)
Neutral atoms / molecules will not dissolve in water (zinc lab / copper lab)
Atoms change charge if they gain or lose electrons (zinc lab / copper lab)
Some atoms can take electrons from other atoms (zinc IN copper lab)
The atoms of the alkali metals have one valence electron that is loosely held to the atom. This can be inferred by the large radius of these atoms, a concept that was developed in the previous unit.
Water molecules are made of two hydrogen atoms and one oxygen atom bonded together. The hydrogen atoms have a positive charge and the oxygen atom has a negative charge. This was determined in the first unit of the year when we split water molecules with electricity, and was more generally developed in 7th grade.
Although water is made of hydrogen and oxygen atoms, water has very different characteristics than hydrogen or oxygen. This was developed in the first unit of the year.
1. Hydrogen is flammable
2. Oxygen allows burning to occur

Part 2

One of the observations that we made of the alkali metals is that the reaction with water converts larger and larger amounts of energy from lithium to cesium.

None of the alkali metals are flammable so the fire and the and the explosions observed cannot be from the metals themselves and must be from the flammable hydrogen produced.

Questions:

If lithium's reaction with water produces hydrogen, why won't the hydrogen light on fire in this reaction?
Sodium's reaction with water also produces hydrogen, and the hydrogen will light on fire but it does not happen immediately.
Potassium's reaction with water will light the hydrogen on fire immediately but this reaction is not nearly as explosive as the reactions between rubidium and water, and cesium in water. Why is that?

Things to consider:

Hydrogen does not light on fire until the gas is about 600 C. How do we explain the temperature increase?
More and more energy must mean more hydrogen. How do you explain this?