Example 1
Question: A small piece of clean rubidium is placed in a beaker of water at room temperature.
Immediately, the rubidium starts spinning around in the water releasing bubbles of gas.
Within a short time, an apparent flame is visible and an audible pop is heard.
Would you describe rubidium as a very active metal, a moderately active metal or a noble (inactive) metal?
Response: The reaction between rubidium and water is rapid at room temperature.
The description of this reaction is similar to that for other very active metals such as sodium or potassium.
Rubidium is therefore a very active metal.
Example 2
Question: A sample of a silvery unknown metal is thought to be either magnesium or silver.
When a clean piece of the sample is placed in water there is no apparent reaction.
When a clean piece of the sample is placed near hot steam, a white substance starts to appear on the surface of the sample.
Is the sample more likely to be silver or magnesium?
Response: Magnesium is a more active metal than silver.
Magnesium will react with steam at high temperatures, but silver will not react under these conditions.
The sample is more likely to be magnesium than silver.
Example 3
Question: Where metal water pipes are in use, they are often made of copper.
Why would you not use a metal such as magnesium to make water pipes?
Response:Magnesium is a more active metal than copper.
Magnesuim would react with the water in the pipes to produce magnesium hydroxide which would produce "hard water" (soap won't lather properly in hard water), causing the magnesium pipe to disintegrate over time.
Copper will not react with the water in the same way so the lifetime of the water pipe will be longer and you will not be contaminating your water!
1Other Noble Metals are; mercury, ruthenium, rhodium, palladium, osmium and iridium.
As you might expect, these noble metals all lie within the same small area of the periodic table!
